paleoethnobotany in the neotropics from microfossils new insights into ancient plant use and...

Journal of World Prehistory, Vol. 12, No. 4, 1998

Paleoethnobotany in the Neotropics fromMicrofossils: New Insights into Ancient Plant Useand Agricultural Origins in the Tropical Forest

Analysis of plant microfossils (phytoliths, pollen, and starch grains) fromarchaeological and paleoecological sediments in the humid Neotropical forestcan provide information on some formerly intractable problems in Americanpaleoethnobotany and archaeology. Each technique has strengths that redressthe other's shortcomings, and all three microfossils can be recovered fromearly sites, securely identified, and dated. Agricultural origins, Pleistocene/Holocene environmental changes, and the evolution of slash-and-burn agri-culture are three important issues that yield substantial results to phytolith,pollen, and starch grain study. Microfossils of a number of domesticates,including maize, manioc, squash, bottle gourd, arrowroot, and leren, havebeen identified in contexts dating from 9000 to 7000 radiocarbon years B.P.The scope and methodology of traditional paleoethnobotany should be ex-panded to routinely include microfossil study.

INTRODUCTION

Paleoethnobotany is normally defined as the study of the interactionsbetween past human societies and the plant world through the analysis ofarchaeobotanical remains (Ford, 1985; Pearsall, 1989; Gremillion, 1997).

1Smithsonian Tropical Research Institute, Box 2072, Balboa, Panama.2To whom correspondence should be addressed at STRI, Unit 0948, APO AA 34002-0948.

KEY WORDS: Paleoethnobotany; Neotropics; phytoliths; pollen; starch grains.

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0892-7537/98/1200-0393$15.00/0 © 1998 Plenum Publishing Corporation

Dolores R. Piperno1,2

As this definition suggests, most studies characterized by their practitionersas paleoethnobotanical focus on the archaeological record. The meaningand scope of paleoethnobotany should be expanded to include plant fossilsfrom nonarchaeological (paleoecological) contexts such as lake and bogsediments, because these fossils provide information on human/plant rela-tionships as surely as do seeds retrieved from ancient hearths around whichpeople sat and prepared meals.

Many researchers, recognizing that no single technique can possiblyidentify the range of seeds, fruits, and underground plant organs exploitedby ancient people, stress the importance of a database consisting ofmultiproxy indicators of plant use and manipulation (e.g., Ford, 1988; Hather,1994; Pearsall, 1989; Watson 1997). The reasons why multiple lines of evi-dence are needed to study cultural uses of plants are many, and they are welldiscussed in the literature. For example, corms, tubers, and other commonlyeaten plant structures, including many seeds, are not sufficiently hard to en-dure the carbonization process; economically important plants often do notproduce enough pollen to be recovered and identified; more humid climatestend to quickly destroy organic remains of plants; phytoliths are well pre-served in many contexts, but they cannot identify some important economicplants; carbonized plant remains may not survive for very long in heavy,clayey sediments typical of the humid tropics, and so on (e.g., Pearsall, 1989).

This article reviews how plant microfossil analysis (phytoliths, pollen,and starch grains) contributes to paleoethnobotanical research in the low-land American tropical forest. Since the author last undertook such a reviewfor the phytolith record of the Neotropics (Piperno, 1991), developmentsin plant microfossil studies have accelerated. Previously unstudied regionsare under scrutiny; new techniques have been introduced and older tech-niques refined. As a result, considerable light is being shed on importantissues pertaining to early plant use and domestication, together with theecological contexts in which plant subsistence strategies evolved throughtime. Such developments in plant microfossil studies are by no meansconfined to the lower latitudes of the New World, but also encompassequatorial Africa (Alexandre et al., 1997; Mercader et al., 1998; Mworia-Maitima, 1997; Runge and Runge 1997), southern China (Zhao, 1998; Zhaoet al., 1998; Jiang and Piperno, 1998), mainland southeast Asia (Kealhoferand Piperno, 1994,1998; Maloney, 1994; Kealhofer and Graves, 1996; Keal-hofer and Penny, 1998), New Guinea (Haberle, 1994; Therin et al., 1997,1998; Torrence and Fullager, 1997), Island Melanesia (Loy et al., 1992;Loy 1994; Athens et al., 1996), and Polynesia (Athens and Ward, 1993;Flenley, 1994).

In the Neotropics, economic and paleoecological reconstructionthrough phytolith and pollen analysis are about to enter their third decade.

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This makes it possible to consider the current state of knowledge in thesefields in light of earlier applications of the techniques, when much basicresearch was still being undertaken. Some important points concerning thepresent state of the art in plant microfossil analysis that are discussed indetail later can be summarized as follows: (1) phytoliths from a number ofdomesticated species—for example, maize (Zea mays L.), squash (Cucur-bita spp.), bottle gourd (Lagenaria siceraria), arrowroot (Maranta arundina-cea), and leren (Calathea allouia)—can be confidently identified; (2) pollenfrom a number of domesticated species—for example, maize, manioc (Man-ihot esculenta Crantz), squash, and chile pepper (Capsicum spp.)—can beconfidently identified, particularly in regions outside the range of their wildancestors; (3) starch grains from maize, manioc, squash, arrowroot, yams(Dioscorea spp.), and achira (Canna edulis) can currently be distinguishedand there is significant potential for more precise identifications in thisemerging field of research; (4) forests and grassland vegetational formationsand vegetation disturbed by humans leave characteristic phytolith and pol-len signatures; (5) direct AMS dating of phytolith and pollen assemblages isa reliable way of establishing their antiquity and starch grains are potentiallydateable by accelerator mass spectroscopy (AMS) as well; and (6) combinedmicrobotanical evidence indicates that human manipulation of Neotropicalplant species, including maize, squash, arrowroot, leren, and, likely, manioc,began in the early Holocene (10,000-7000 B.P.) in a region from lowerCentral America to northwestern South America.

PHYTOLITH ANALYSIS

Phytolith Production

A great many tropical angiosperms and gymnosperms heavily silicifytheir vegetative and reproductive organs, resulting in the production ofcopious amounts and many kinds of phytoliths that are ultimately depositedas discrete particles into tropical sediments. The notion prevalent in muchof the English-language botanical literature for much of the 20th centurythat only the Poaceae and a few other monocotyledonous families wouldleave an informative phytolith record can be put to rest. As ongoing OldWorld tropical research also demonstrates, phytolith production and mor-phological patterns are nonrandom, predictable, and now well understood(Pearsall et al, 1995; Runge, 1995; Runge and Runge, 1997; Kealhofer andPiperno, 1998), Temperate and Boreal zone representatives of the familiesand genera studied in the Neotropics follow patterns almost identical totheir low latitude relatives (e.g., Bozarth 1987, 1992; Hodson et al, 1997;

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Ollendorf, 1992; Sangster et al, 1997). Phytolith analysts know in whichfamilies and genera phytoliths are most likely to be found and in whichthey are least likely to be found, and they have essentially replicated theextensive research on phytolith production that was carried out by Germanbotanists during the first third of the 20th century (see Piperno, 1988, fora review of this literature).

Another strong and consistent pattern of phytolith production is thatangiosperms that contribute high numbers of vegetative structure phytolithsmay sometimes, but not always, heavily silicify their seeds and fruits. Con-versely, angiosperms that do not heavily silicify their vegetative structuresseldom produce reproductive organ phytoliths. The demonstrated patternsof phytolith production allow researchers to effectively build large modern-type collections for a diverse flora because we know which plants andindividual structures should reward our efforts. The patterns also facilitatethe development of identification procedures for domesticated plants, be-cause we can be confident that diagnostic forms produced in cultivars willnot also be made in unrelated species that have not been analyzed.

Table I contains summaries of phytolith production in Neotropicalplants. They are little changed from those given in Piperno (1991) by theresults of research in the 1990s, even though more than 200 additionalnongrass species, including about 170 trees and shrubs, from a larger numberof families and a broader geographic area were incorporated into the au-thor's modern reference collection. This collection now includes more than2000 species from 108 families. Another large (ca. 1000 species) collectionof Neotropical species is the one housed in Pearsall's laboratory at theUniversity of Missouri. In many plants, we analyzed replicate samples ofthe same species from different populations in order to judge what kindof infraspecific variability existed in phytolith production. The numeroustypes of phytoliths referred to here were produced with a high degree offidelity, regardless of the location where the plant was sampled. Indeed,similarities in the production and localization of solid silica in the samespecies and among closely related ones are such that we can begin to talkwith some confidence about plants of all kinds having specialized phytolith-making cells or, perhaps, enzymes that are turned on to deposit solid silica.

Our pre-1991 efforts to build a modern reference collection concen-trated on accumulating a very good sample of phytoliths from the markedlyseasonal deciduous and semi-evergreen forests of Central America andnorthern South America, where most archaeological sites investigated tothat point were located. In the 1990s, we set out to improve the collectionfor the wetter and more speciose forests that still dominate the Darienprovince of Panama, where many trees important in the South Americanforest reach their northernmost limits (Piperno, 1994a). We also began to

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Table I. Patterns of Phytolith Production and Taxonomic Significance among Tropical Plants

Families in which production is high, phytoliths minimally specific to family are common,and subfamily and genus-specific forms occur, sometimes widely in the family

Monocotyledons: Arecaceae,a Cyperaceae,a Heliconiaceae,ab Marantaceae,ab Musaceae,a

Orchidaceae, Poaceae,a Zingiberaceaea

Dicotyledons: Acanthaceae, Annonaceae, Burseraceae,a Chrysobalanaceae,a Compositae,Cucurbitaceae,a Dilleniaceae, Magnoliaceae, Moraceae, Podostemaceae, Ulmaceae,a

UrticaceaePteridophytes: Equisetaceae, Hymenophyllaceae, Selaginellaceae

Families in which production is not high in many species, but where family and genus-specific forms are present

Pinaceae, Euphorbiaceaea

Examples of important families in which phytoliths have not been observed, or where pro-duction is rare and nondiagnostic

Amaranthaceae, Araceae, Cactaceae, Chenopodiaceae, Dioscoreaceae, Liliaceae, Melas-tomataceae, Myrtaceae, Podocarpaceae, Rubiaceae, Sapindaceae, Solanaceae

Examples of subfamily and genus-specific forms with their cultural and paleoecological sig-nificance

I. Herbaceous Plants

Zea luxurians, Tripsacum, Arundinella, Polypogon; Bambusoideae — Chusquea, Pharus,Streptochaeta, Neurolepis, Maclurolyra; Cyperus/ Kyllinga and other sedge genera; Hell-coma; Trichomanes, Mendoncia, Podostemum, Calathea, Stromanthe, and other Maranta-ceae genera

Explanation: Zea luxurians (Race Guatemala), a teosinte endemic to the Guatemalan low-lands, has species-specific fruitcase phytoliths. Tripsacum is a near relative of maize. Itsphytoliths are more easily separable from those of teosinte than are its pollen grains be-cause morphologic differences in phytoliths from these taxa are considerable. Arundinellais a tall grass whose cross-bodies are confusable with maize, but it contributes other genus-specific phytoliths. Podostemum attaches to rocks in swiftly flowing rivers. Trichomanes isa fern that grows attached to tree trunks in humid, lowland forest. Mendoncia is a good in-dicator of a humid tropical forest. Calathea and other Marantaceae grow in the moist un-derstory of a tropical forest. Bamboos are commonly used for construction, bedding, and amyriad of other purposes in the American tropics. Some (Chusquea) are excellent indica-tors of mature forest. Trichomanes, Mendoncia, Marantaceae, and bamboos like Chusqueacan be used to document older growth forest, and to follow the course of forest clearingby humans. Sedges and Heliconia are major indicator taxa for early successional growth fol-lowing human disturbance.

II. Trees and Other Woody Plants

Magnolia, Talauma, Protium, Bursera, Trema, Poulsenia, Celtis, Hedyosmum, Pinus spp.,Unonopsis/Oxandra, Trema, Curatella

Explanation: These taxa are common trees and shrubs of various kinds of mature tropicalforest (montane, lowland, semi-evergreen, evergreen) and successional growth. Curatella isa major indicator taxon for serious land degradation and anthropogenic savanna in thetropics.aReproductive structures (fruits and seeds) also produce high amounts of diagnostic phytoliths.bUnderground organs (roots, tubers, and corms) may contribute high amounts of diagnos-tic phytoliths.

seriously consider the terra firme (dry, upland) and floodplain Amazonianforests (Piperno and Becker, 1996), and we incorporated more trees andgrasses typical of the Central and South American cool and mountainoustropics—from elevations above 1200 m. Finally, we investigated phytolithsin a large number of close relatives of some major plant domesticates inorder to develop identification criteria for the crop plants where possible.

We do not yet have an answer to the question of why some plants andnot others make phytoliths, but the facts that (1) families and genera exhibita strong tendency either to silicify or not to silicify their organs and (2)production is often localized in particular kinds of tissues (e.g., leaf andseed epidermis, fruit pericarp) indicate a functional significance for phyto-liths. Two nonmutually exclusive hypotheses for why mechanisms to depositsolid silica were selectively favored by many plants head the list that shouldbe tested. One is that phytoliths, like lignin and many chemical substancesmade by plants, are antiherbivorous and antipathogenic in design. Investiga-tors have long been aware that depositing large amounts of solid silicabenefits certain crop grasses by increasing their resistance to fungi andstem-boring insects (e.g., Sangster and Hodson, 1997). Although there isa growing literature on tropical plant/herbivore and pathogen interactions(e.g., Coley and Barone, 1996), the role that phytoliths may play in plantdefense has not been considered. The following points illustrate that thisis an area worthy of study.

There are thousands of species of "herbivores" in a tropical forest,most of them being small insects such as ants, caterpillars, and beatles thatfeast on the leaves of many species and may cause severe defoliation anddecreased fitness. By incorporating high amounts of solid silica, plants canbetter defend themselves because phytoliths toughen plant structures andmake them harder to eat and digest. Toughness, in fact, has been calledthe most effective defense that can be marshaled by plants (Coley andBarone, 1996). However, toughness is a less viable option when leaves areyoung and need to expand, so young leaves fortify themselves largelythrough chemical means, leading to the well-documented greater produc-tion of toxic compounds in young as compared to mature leaves (Coleyand Barone, 1996).

Very little is known about the time of solid silica formation in mosttropical plants, but if it is anything like that documented for some temperateand boreal zone grasses and trees (Hodson et al., 1997; Sangster and Hodson,1997; Sangster et ai, 1997), then it would increase with age, perhaps takingplace mainly after the leaf has expanded and could begin to mechanicallydefend itself. This might suggest a two-pronged approach to plant defense,with phytoliths and other compounds such as lignin assuming a more impor-tant role after the leaf has matured. Once plants deposit solid silica, it can

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be carried unaltered until the leaf drops, negating or lessening the need forthe expensive turnover of chemical compounds that might be particularlytroublesome for long-lived (average 3-14 yr) leaves of tropical species.

These points are largely speculative at this time and do not directlyaddress the question of why some plants do not make phytoliths. However,evolutionary strategies are often nothing if not trade-offs relating to thecosts and benefits of resource allocation. Hence, questions relating to thewhys and why nots of phytolith production should benefit from studies ofthe relative costs and advantages to plants of making phytoliths at any stageof their development vs. manufacturing chemical compounds or investing inother kinds of mechanical defenses like lignin.

Another good reason why plants might want to make phytoliths is thatsilicon dioxide may ameliorate the toxic effects of aluminum (Hodsonand Evans, 1995). Aluminum oxides are common components of highlyweathered tropical soils, and are ingested by plants through the transpira-tion stream along with other soluble substances in groundwater. Becausesilicon and aluminum have been shown to co-occur in plant tissues ofsome plants, the mechanism for detoxification may be a sequestration ofaluminum by the silicon (Hodson et al., 1997).

Phytolith Taxonomy and Identification

Discussions of phytolith taxonomy in the botanical and archaeologicalliterature of the 1970s and early 1980s were sometimes dominated by whatcame to be known as the "redundancy" and "multiplicity" issues (Rovnerand Russ, 1992). It was well understood from the many studies of grassleaf phytoliths carried out by botanists to that point that any single genusand species of the Poaceae might contain several different types of phytol-iths, and that any one of these could be found in another grass (Piperno,1988). Although a limited number of other plant families had been closelystudied, there were concerns that phytoliths might never provide the taxo-nomic precision necessary for subsistence and environmental reconstruc-tions. With the initiation of the modern period of archaeological phytolithresearch in the late 1970s and 1980s and the increased attention it broughtto a wider spectrum of plants and plant structures, it started to become clearthat taxonomically significant forms were common in the plant kingdomand that genus-level identifications were possible, even in some grasses(Bozarth, 1987; Pearsall, 1978, 1989; Piperno, 1984, 1985, 1988, 1989).

Research undertaken in the 1990s further demonstrates that phytolithredundancy and multiplicity are not serious issues in many tropical plants(Piperno, 1993; Piperno and Pearsall, 1993a,b, 1998a; Veintimilla, 1998).


Phytolith morphology exhibits a strong correspondence to a plant's taxo-nomic affiliation, indicating a strong genetic influence controlling plantsilicification. Many families produce phytoliths with diagnostic shapes (Ta-ble I). Genus-level discrimination of some important trees and herbaceousplants is possible (Table I; Figs. 1-4). The fruits and seeds of many angio-sperms produce single or very few types of phytoliths often diagnostic togenus and also commonly distributed into archaeological and paleoecologi-cal sediments (Figs. 4-6) (Piperno and Pearsall, 1993a,b; Piperno andBecker, 1996). Species-level discrimination is possible with some plantsthat have been artificially altered in a fundamental way from their wildstates—that is, crop domesticates (see later).

A survey of silica bodies (dumbbells, cross-shapes, saddle shapes) inmore than 300 Neotropical grass species revealed that some contributeindividual, diagnostic phytoliths, including maize's wild ancestor, teosinte,

Fig. 1. Center, a genus-specific phytolith from the leaves of Talauma (Magnoliaceae) frommodern soils underneath tropical montane forest in Panama.

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Tropical Paleoethnobotany Through Microfossil Analysis

Fig. 2. Center, a genus-specific phytolith from the leaves of Magnolia (Magnoliaceae) fromLate Pleistocene-age lake sediment from Panama. Palynologists are unable to distinguish thepollen of the closely related taxa Talauma and Magnolia.

and its near relative, Tripsacum (later this chapter) (Piperno and Pearsall,1998a) (Figs. 7, 8). The fact that these two grasses contribute distinctivephytoliths is not really surprising because they are the only New Worldgrasses that enclose their grains with a hard, cupulate fruitcase in whichthe diagnostic forms originate. Also, bamboos, which are often informativeindicators of past climate and vegetation and obviously were well used inprehistoric economic systems, often contribute genus and tribal-specificshapes (Table I). Most other wild grasses produce less specific types, butit remains that phytoliths offer a much better interpretation of past grasscommunities and cultural/grass interactions than pollen because they, un-like pollen, can be identified below the family level.

As is the case for phytolith production, phytolith morphology in family,genera, and species is congruent across the world (Bozarth, 1992; Ollendorf,1992; Runge, 1995; Runge and Runge, 1997; Chen and Jiang, 1997; Houyuan

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Fig. 3. A probable genus-specific phytolith from the leaves of Perebea xanthochyma (Mora-ceae). Palynologists often cannot discriminate genera in this family.

et al., 1997; Kealhofer and Piperno, 1998; Zhao et al, 1998). In otherwords, like pollen grains, phytoliths from sedges, composites, pines, grasses,Magnolias, elms, and other cosmopolitan plants have the same basic formregardless of whether they are from an arctic tundra or a tropical rainforest. Such patterns further indicate a strong genetic influence on phytolithmorphology and indicate that phytolith shapes are not likely to be subjectto the whims of local environmental variability.

We presently have little understanding of why tropical plants make somany kinds of phytoliths. Some phytolith shapes (e.g., those from dicotyle-don hair cell and hair bases and seed epidermes) are simply mineralizedreplicas of the former living cell, this occurring when the cell is completelysilicified or when the cell wall becomes encrusted with silica. Many others,however (e.g., from the Marantaceae, Palmae, and Poaceae) cannot be soeasily understood because they involve a silicification of the interior of thecell, resulting in diverse forms unlike that of the cell.

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Fig. 4. A genus-specific phytolith from the fruit of Trema micrantha (Moraceae).

It is possible that as with pollen (Dajoz et al., 1998), phytolith morpho-logical variation is associated with increased fitness, but there are no dataat present to indicate what the selective pressures on plants may havebeen to induce morphological change. Major global climatic changes andextinction events relating to vertebrate and other herbivore evolution areamong the candidates that perhaps should be considered. It is, at least,clear that phytolith morphology has changed through time in certain plantfamilies. For example, the most primitive living grasses, such as bamboosand species in the subfamily Arundinoideae, have taller, thicker, and moreangled silica bodies than grasses derived later in time, such as mainstreamspecies in the Chloridoideae and Panicoideae (Piperno and Pearsall, 1998a).

Phytoliths in Plant Domesticates and Other Important Economic Plants

The sheer abundance of different species in the tropical flora has givenpause to archaeologists who would like to consider the available phytolith


Fig. 5. Genus-specific phytolith from the seeds of Mendoncia spp. recovered from modernsoils underneath tropical montane forest in Panama.

record with regard to its relevance to early plant domestication. This is alegitimate concern, particularly when applications of a technique are newand basic reference collections are being constructed for a complex flora.However, with the accumulation of the substantial amount of informationon phytolith production and taxonomic patterns just described, phytolithinvestigators have been able to move onto more tightly focused and re-stricted sets of taxonomic problems, involving studies of those importantcrop plant species that produce high amounts of phytoliths in promisingshapes. In the Neotropics, six crop plants stand out in such a manner: maize,three members of the Cucurbitaceae family [Cucurbita spp. (squashes andgourds), Lagenaria siceraria (bottle gourd), and Sicana odorifera (cassaba-nana)] and the Marantaceae tubers Maranta arundinacea (arrowroot) andCalathea allouia (leren) (Table II). Identification criteria in most of themrelies heavily on phytoliths found in the reproductive structures of the

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Fig. 6. A family-specific phytolith from the fruit of Altis spinosa (Ulmaceae).

plants, an advantageous factor because, as discussed, such phytoliths canbe particularly diagnostic. I begin with maize.

Considerable effort during the 1990s has been invested in developingreliable identification criteria to differentiate maize from wild Neotropicalspecies, including its putative wild ancestor, teosinte. Research on maizephytoliths in archaeological contexts began with a study by Pearsall (1978)that focused on the size of a type of grass phytolith called "cross-shaped"(hereafter also called "cross-bodies"), produced predominantly in leaves.Subsequent research by the author (1984, 1988) explored morphologicaldifferences in cross-bodies and found them also to be useful indicators ofmaize presence. Cross-bodies were divided into eight different morphologi-cal "variants" based on their three-dimensional structures. The combinationof size and three-dimensional shape resulted in a significant statistical sepa-ration of cross-bodies from maize and wild grasses using a multivariate(discriminant function) analysis (Piperno, 1988).


Fig. 7. A Tripsacum-specific fruitcase phytolith from T. lanceolatum. It has markedly serratededges and possesses ridges on the top.

In order to test the viability of the technique in maize's homeland,Mexico, expand the applications to regions such as the Amazon Basin, andbring the research to a point of closure, the author and Pearsall completeda study in which the leaves, other vegetative structures, and inflorescencesof numerous previously untested tropical grasses were analyzed using thesame size and shape criteria. This brings the total number of wild speciesinvestigated to more than 350 (see Piperno and Pearsall, 1998a, for a list).These were compared with 25 modern Latin American maize races and allfive extant races of teosinte, including maize's putative wild ancestor Balsasteosinte. The non-Zea wild grasses were chosen on the basis that they werethe most likely to possess cross-bodies because of taxonomic affiliation andwere the most common reported in forest, mangrove, anthropogenic, andother Neotropical habitats. Replicates of every species of maize's closerelative Tripsacum and of every genus and most species of bamboos re-ported from the Neotropics were analyzed (Table II).

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Fig. 8. A fruitcase phytolith from Balsas teosinte. It is produced in the same tissue as phytolithillustrated from Tripsacum but lacks serrated edges and ridges along the top.

The overwhelming majority of the wild grasses have cross-shaped phy-toliths significantly smaller and/or structured differently from those ofmaize. A new discriminant function analysis incorporating all wild grassesalong with maize separated phytoliths into two distinct groups, maize andwild, with a high degree of statistical confidence (D. R. Piperno and D. M.Pearsall, unpublished data).

We identified a few non-Zee wild grasses [Arundinella deppeana(leaves), Maclurolyra tecta (leaves), and Tripsacum spp. (fruitcases); noneused today in indigenous tropical economies] that contributed high percent-ages of large-sized Variant 1-type cross-bodies, as does maize. (The leavesof Tripsacum spp. do not possess maize confusers.) However, these grassescontribute several distinctive types of cross-body and other phytoliths notfound in maize that are easily recognized in soils (Fig. 7) (see also Pipernoand Pearsall, 1993a, 1998a, for illustrations). This means that a completelysecure maize identification using cross-bodies rests on a verification using


these distinctive phytoliths that these grasses are not present. There areother ways to identify maize in archaeological samples that can be appliedindependently or in place of the discriminant function analysis. For example,if large-sized (greater than 16 micrometer) cross-bodies constitute morethan 10% of all cross-bodies counted, and if they are predominantly (morethan 50%) Variant 1, then maize is almost certainly present because wildgrasses with the exception of the three noted lack these characteristics.

Importantly, this grass study informed us that in maize's homeland,southwestern Mexico, identification of maize based on cross-body studyrequires an assemblage approach because nearly all races of teosinte, includ-ing Race Balsas, likely maize's direct ancestor (Doebley, 1990), contributecross-shaped phytoliths that are maize mimics (Piperno and Pearsall,1993a). The confuser phytoliths, like those of Tripsacum, originate largelyfrom the fruitcases and ear sheaths of the plant, although Nobogame teo-sinte, presently endemic to higher and drier elevations in Mexico, alsoproduces maizelike cross-bodies in its leaves. This situation is made lessproblematic by the fact that other unique phytoliths are produced in teosintefruitcases that should signal teosinte presence archaeologically (Pipernoand Pearsall, 1993a). In contrast to fruitcase cross-bodies, those from the

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Table II. Crops Plants with Diagnostic Phytoliths

Zea mays (maize), Cucurbita moschata, C. ficifolia (squashes), Lagenaria siceraria (bottlegourd), Sicana odorifera (cassabanana), Calathea allouia (leren), Maranta arundinacea(arrowroot)

Number of species in the crop plants' families studied

1. Maize was compared with about 350 species of Neotropical grasses, including multiplereplicates of leaves, fruitcases, and tassels from every race of teosinte and replicates ofthese structures from every known species of Tripsacum; 25 different maize races wereevaluated.

2. Squash, bottle gourd, and cassabanana were compared with replicates of 41 speciesfrom 22 different genera in the Cucurbitaceae. Domesticated squashes were comparedwith 7 wild and 1 semidomesticated species of Cucurbita, including 11 different popula-tions of C. ecuadorensis from Ecuador, and multiple replicates of five different populationsof C. argyrosperma ssp. sororia from Panama.

3. Leren and arrowroot were compared with 22 species comprising 8 different genera inthe Marantaceae.

Comments

1. Maize's wild ancestor, teosinte, produces diagnostic fruitcase phytoliths. Cross-bodiesfrom the leaves of Balsas teosinte, maize's likely direct ancestor, are much smaller thanand structured differently from those of many races of maize.

2. There is infraspecific variation among domesticated species of Cucurbita that needs fur-ther study. Spherical, scalloped phytoliths appear to be confined to the tribe Cucurbiteae,which also includes the Old World melon Benincasa.

leaves of Balsas teosinte can be readily separated from most maize races(Piperno, 1988; Piperno and Pearsall, 1993a).

Marked differences are also apparent between phytolith assemblagesfrom teosinte fruitcases and maize cobs, which produce siliceous bodiesprimarily in the cupules and glumes (Mulholland, 1993; Piperno and Pear-sall, 1993a). For example, teosinte possesses high numbers of decoratedepidermal and decorated circular phytoliths, whereas in maize, most circularbodies are undecorated, even in the most primitive races of maize knowntoday from Mexico and Peru (Piperno and Pearsall, 1993a, unpublisheddata) (Figs. 9, 10).

In summary, results to date on phytolith production in maize, teosinte,and other grasses allow a number of observations to be made about thephytolith record of southwestern Mexico. If teosinte seeds were used as acommon food item, they should be detectable using the phytoliths thatderive from their fruitcases. Conversely, if the strategy of wild maize utiliza-tion was the consumption of immature ears as vegetables and the seedswith their hard fruitcases were never commonly collected and processed,

Fig. 9. A decorated circular phytolith from the fruitcase of Balsas teosinte.


Fig. 10. Undecorated circular phytoliths from a cob of maize, Race Maiz Ancho from Mexico.

as several students of maize origins have proposed (e.g., Harlan, 1992),fruitcase phytoliths should be missing from sites dating to the early Archaicperiod. Neither teosinte nor maize should be confused with their nearrelative Tripsacum using fruitcase and cob phytoliths, and phytoliths fromTripsacum leaves are also differentiable from maize. Phytolith assemblagesfrom teosinte fruitcases and maize cobs are differentiable. Finally, leafcross-bodies may play an important role in detection of early cultivatedmaize in maize's hearth if teosinte and Tripsacum fruitcase phytoliths canbe ruled out from representation.

We should not be deterred by the fact that we sometimes have to usean assemblage approach to identify maize. Bone chemistry studies employa similar methodology. For example, when high delta I3C values are foundin archaeological bone samples suggesting a diet heavy in C4 plants likemaize, nitrogen isotope ratios must also at times be examined to rule outthe possibility of heavy marine food contribution to the diet, because marinefauna have carbon isotope signatures that may mimic maize (Norr, 1995).

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Treating the diversity of phytolith shapes in grasses as independent linesof evidence can only improve the accuracy of archaeological phytolith iden-tification.

Cucurbita and Other Cucurbitaceae

Although maize has taken center stage in discussions of phytolithsin archaeological sediments, other important, domesticated plants can beidentified with phytoliths. Cucurbita and other important Cucurbitaceaecontribute large numbers of distinctive phytoliths in the rinds of their fruits(Piperno et al., 1998) (Table II) (Figs. 11-16). Rinds produce single to veryfew types of phytoliths. Cucurbita phytoliths are large (ranging from about56 to 120 micrometers in mean length), more or less spherical, and havedeeply "scalloped" (Bozarth, 1987) surfaces (Figs. 11 and 12). They were

Fig. 11. A spherical, scalloped phytolith from the rind of Cucurbita moschata. The scallopsare round, deep, and regularly distributed.


Fig. 12. A phytolith from Cucurbita lundelliana like the one in Fig. 11, turned on its side to revealthe different pattern of scallop shape and size on the hemispheres of Cucurbita phytoliths.

compared with multiple replicates of phytoliths from 41 other species inthe Cucurbitaceae (Piperno et al, 1998) revealing that they are distinguish-able on the basis of both morphology and size from other genera in thefamily (Figs. 13-16). Phytoliths from wild Cucurbita are significantly smallerthan those from domesticated species (Piperno and Pearsall, 1998b, p. 191;Piperno et al., 1998). Bottle gourd and a cucurbit fruit called cassabanana(Sicana odorifera), which was domesticated in the lowland Neotropics, alsocontribute distinctive, large rind phytoliths (Figs. 13 and 14), although inbottle gourd phytolith production can be spotty. In all of the Cucurbitaceae,phytolith size appears to be highly correlated with fruit and seed size,indicating that, as with archaeological seed analysis (Smith, 1997), increasein size through time probably indicates manipulation and genetic changeunder human cultivation (Piperno et al., 1998) (Fig. 17).

Another interesting feature of phytolith production in Cucurbita isthat domesticated populations often contribute far fewer phytoliths thando wild ones. This may be a case where silicifying the outermost part of

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Fig. 13. A phytolith from Lagenaria siceraria (bottle gourd). It is distinctive because it haslarge, often elongated, and irregularly distributed scallops on one side of the phytolith, andis hemispherical.

the fruit is more beneficial when the plant is wild and commonly preyedon by herbivores than when the plant is brought under human control.Also, humans probably consciously selected for softer rinds, which wouldmean an emphasis on those mutant wild gourds that produced fewer phy-toliths.

Tuber Crops

Very few Neotropical plants that were domesticated for their subterra-nean organs produce a valuable phytolith record. Starch analysis will proba-bly become the primary source of information for this area. Exceptions aretwo now-minor crops of the lowland tropical forest, leren (Calathea allouia)and arrowroot (Maranta arundinacea). In these plants, distinctive phytoliths

413Tropical Paleoethnobotany Through Microfossil Analysis

Fig. 14. A phytolith from Sicana odorifera. It has one hemisphere that is markedly conicaland faintly decorated (compare with Cucurbita and Lagenaria).

are formed in the seed epidermes, which, like fruit rinds, produce singleto very few types of phytoliths (Fig. 18). Comparison of phytoliths fromthese cultigens with wild progenitors is not possible because wild ancestorsare unknown for both of them. However, analysis of large numbers ofspecies in their family indicates that a species-specific identification in ar-chaeological contexts is likely a secure one (Table II).

Other tree and root crops such as pineapples (Ananus comosus) andachira (Canna edulis) produce phytoliths that also occur in other membersof their family, and here identification must rest on the inferred absenceof these possible confuser plants in the prehistoric regional flora. A fewcrop plants have phytoliths in need of further study before their diagnosticpotential is known. One is the common bean, Phaseolus vulgaris, whichproduces a type of pod phytolith (Bozarth, 1990) that may be larger thanthose in other Neotropical taxa. It should be noted that this phytolithappears to be less resistant to destruction in tropical sediment than others

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Fig. 15. Scalloped phytoliths from a wild species in the Cucurbitaceae, Peponopsis adhaerens.They differ from domesticated Cucurbitaceae in having small and indistinct scallops, littledifference in the decoration of the hemispheres, and in overall size. Also, they often are notspherical, but are flattish (see also Fig. 16).

discussed here, possibly because it is formed by cell-wall silicification. Ithas not been observed in any sediment sample studied to date by theauthor. In summary, paleoethnobotanists in possession of large comparativecollections should be able to identify phytoliths from maize, squash, bottlegourd, cassabanana, leren, and arrowroot with a high degree of confidence.Identification of most other crop plants will likely have to rely on othermethods.

Phytoliths in Sediments

The 1990s saw the growth and refinement of phytolith analysis throughthe retrieval and identification of phytoliths from "modern" archaeological,

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Fig. 16. Scalloped phytolith from a wild species in the Cucurbitaceae, Cionosicys macrantha(see caption for Fig. 15).

and paleoecological sediments from previously unstudied regions (the Bra-zilian Amazon, the Colombian Cauca Valley and Amazon, and Belize) andcontexts (natural soils underneath modern forest; deep sea sediments).Phytoliths sampled from the uppermost soils underneath various extantvegetational formations along temperature and precipitation gradients indi-cate that mature forests of several types (e.g., lowland evergreen and semi-evergreen, montane), along with grasslands and vegetation disturbed byhumans at varying scales of intensity, leave readable phytolith signatures(Piperno, 1993; Piperno and Pearsall, 1998b, pp. 177-178; Piperno andBecker, 1996). Archaeological phytolith results are summarized later (seealso Piperno and Pearsall, 1998b). Because phytoliths and pollen frompaleoecological sequences were often analyzed in tandem and the twomicrofossil indicators often closely agreed with respect to environmentalhistory, phytolith results can be grouped with those from pollen, describednext. Archaeological and paleoecological sediments also contain many un-

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Fig. 17. Graph of the relationship between phytolith length and fruit length in modern wildand domesticated Cucurbita. A highly significant linear correlation exists between the twovariables (R2 = 0.894; p < .001). A similarly strong significant correlation exists betweenphytolith thickness and fruit/seed size. Closed circle: C. argyrosperma ssp. sororia (wildspecies); triangle: C. pepo ssp. texana (wild species); closed square: C. ecuadorensis (a semido-mesticated species); hexagon: C. ficifolia (domesticated species). (From Piperno and Pear-sail, 1998b).

known (and highly distinctive) phytoliths that should be named as themodern reference collection is expanded (Figs. 19 and 20).

POLLEN ANALYSIS

Introduction

Although palynology has a deeper history than phytolith analysis,pollen analysis in the humid tropics is still a young science. Not so longago, there were real concerns among some practiced palynologists of thetemperate zone as to whether the lowland tropical forest would leave auseful pollen record. The worries (e.g., Faegri, 1966) centered aroundwhether a flora that was largely pollinated by insects could produce anddisperse enough pollen to be represented in fossil contexts, if pollen couldsurvive under circumstances like high rates of decomposer activity that

Fig. 18. Phytoliths from the seeds of Calathea allouia (leren). They are diagnostic becausethey have flat and undecorated upper bodies, in contrast to all other studied species inthe Marantaceae.

typified tropical habitats, and whether regional floras that contained thou-sands of species of higher plants were amenable to the development ofpollen keys.

Nevertheless, spurred by the success of a pollen application in theMaya heartland (Deevey et al, 1979), investigators set out to study thesequence of past vegetational and climatic changes throughout the lowlandNeotropics. Old, permanent bodies of water turned out to be much morecommon in areas originally or still covered by lowland tropical forest thanhad been believed, pollen preservation in these water bodies was excellent,and, most surprisingly, pollen content (influx) was sometimes comparablewith that from lakes in the temperate zone (e.g., Leyden, 1984,1985; Bushand Colinvaux, 1988, 1990; Frost, 1988; Piperno et al., 1990; Bush et al,1992). Although many taxa could not be identified in these early studies,the furious construction of reference collections that often accompaniedthis research allowed a broad reconstruction of environmental history,

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Fig. 19. Unknown, diagnostic phytolith recovered from modern soils underneath tropicalevergreen forest in the central Amazon basin.

including the crucial Pleistocene to Holocene transition, in regions rangingfrom Guatemala to the interior of the Amazon Basin for the first time.

Interestingly, pollen and phytoliths from lakes and swamps located inarchaeological study regions even far removed from ancient centers ofcivilization were revealing systematic interference with, and sometimesdestruction of, the natural vegetation thousands of years ago that appearedto reflect early forms of plant manipulation by humans and slash and burnagriculture (Monsalve, 1985; Rue, 1987; Bush et al, 1989; Piperno et al,


Fig. 20. Unknown, diagnostic phytolith probably from the Burseraceae, from the same contextas Fig. 19.

1991). The popular notion of the noble tropical savage who lived in harmonywith the forest and minimally disrupted its natural processes was imperiled.Often, too, the evidence for a human presence and interference with thevegetation predated existing archaeological records, not a radical findingwhen one considered that aceramic people who fashioned their bowls andtools out of wood would not be so easily traced with an archaeologicalrecord. On the whole, the paleoecological evidence indicated that societiesalready fully organized as shifting agriculturalists were widespread in the

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lowland tropical forest by 7000 B.P.-5000 B.P. It also pointed to lower-level human interference with the vegetation during the early Holocene.

Pollen Research Since the Late 1980s

Environmental Reconstruction

As with phytolith analysis, tropical palynology's most significant devel-opments since the late 1980s with regard to putting to rest earlier concernsabout its viability, substantiating the results generated during the 1980sand early 1990s, and refining archaeological subsistence and environmentalreconstructions, involved three areas of research: (1) building large, modernreference collections for the natural and domesticated flora; (2) systemati-cally sampling the modern pollen deposited into different extant vegeta-tional formations; and (3) further investigating pollen occurrence and agein a variety of ancient sedimentary contexts, including archaeological sites,lakes, and deep sea sediments.

Very large (at least 2000 and up to 10,000 species) modern collectionsof pollen are now available for a considerable number of study regions,including the Brazilian Amazon (Colinvaux et al., 1998), Cauca and Magda-lena valleys of Colombia and the western Amazon Basin (Herrera andUrrego, 1996), and the Pacific and Caribbean watersheds of CentralAmerica (Roubik and Moreno, 1992; J. Jones, B. Leyden, and M.B. Bush,personal communication, 1998). The number of identifiable taxa in pollendiagrams typically exceeds 200 now, genus-level identifications are common,and the proportion of unknowns in some regions has been effectively halved(E. Moreno and M.B. Bush, personal communication, 1998).

Accompanying these studies have been detailed evaluations of therelationship of the modern pollen rain to the regional vegetation in termsof pollen representation and dispersal, taxon abundance, and the identifica-tion of indicator forest taxa for various temperature and rainfall gradients(Bush, 1991,1992,1998; Bush and Rivera, 1998a; Rodgers and Horn, 1996).Such analyses refine the interpretation of fossil pollen in relation to bothnatural and human-induced changes in the vegetation. Bush and Rivera'sstudies concentrated on mature, well-described forests in permanent plotsfrom Panama, Ecuador, Brazil, and Costa Rica under little or no humanpressure. Their results substantiated the interpretations of the magnitudeof climatic and vegetational change that accompanied the Pleistocene toHolocene transition in lower Central America (Bush and Colinvaux, 1990;Piperno et al., 1990; Bush et al., 1992). If anything, these studies had some-what underestimated the degree of cooling, and, therefore, probably of


drying that marked the late glacial period. The massive environmentalchanges that accompanied the end of the last ice age in the lowland tropicalforest have been recorded in many other pollen sequences published sincethe late 1980s (e.g., Leyden et al, 1993; Van der Hammen and Absy, 1994;Behling, 1996; Colinvaux et al., 1996a,b; Salgaldo-Labouriau et al, 1997;Athens and Ward, 1998; see also Piperno and Pearsall, 1998b, pp. 90-107).It is increasingly clear that the low latitudes of the New World experiencedenvironmental oscillations at the close of the Pleistocene no less profoundthat those that occurred elsewhere on the globe and that have long beenassociated with major economic transitions.

Why the lowland tropical forest produces and disperses much morepollen than was once believed possible, making a viable paleoecologicalrecord possible, has also been elucidated by studies of the modern pollenrain. It seems that the reproductive characteristics of tropical plants (monoe-cious vs. dioecious), in addition to the particular pollination system theyemploy, play major roles in determining how much pollen is made andthen liberated in a tropical forest (Bush, 1995; Bush and Rivera, 1998b).There are many insect-pollinated plants that are dioecious, which meansthey outcross, and because it is unlikely they will find conspecifics next tothem in a species-rich forest, they require relatively long distance pollentransport and, likely, relatively greater amounts of pollen in their flowers.These taxa, in addition to the fewer wind-dispersed plants, become thepotent suppliers of pollen that subsequently becomes amply representedin fossil diagrams (Bush, 1995; Bush and Rivera, 1998b). Although themany lowland forest taxa that are monoecious and pollinated by insects willstill be largely blind or dramatically underrepresented in pollen diagrams,knowledge of which plants are likely to enter a pollen record makes thebuilding of reference collections for a complex flora a more feasible andefficient endeavor.

The modern pollen studies are also sustaining interpretations relatingto early human interference with the forest and its clearance by slashand burn agricultural techniques that were made on the basis of earlierpaleoecological research cited previously. Very low levels of pollen fromherbaceous and secondary woody taxa that were used as indicators ofancient human disturbance occur in the modern forests, including thosefrom the driest areas, indicating that the effects of human forest clearanceand other disturbance can often be disentangled from the effects resultingfrom natural perturbations. Studies carried out in the 1990s continue toprovide evidence for human manipulation of the lowland tropical forestduring the early Holocene, together with the emergence of slash and burnagriculture between 7000 B.P. and 4200 B.P., depending on the region (e.g.,Mora et al, 1991; Jones, 1994; Behling, 1996; Pohl et al., 1996; Goman and

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Byrne, 1998; Piperno, 1994a; Piperno and Pearsall, 1998b; Pope and Pohl,1998; Athens and Ward, 1998).

Identification of Crop and Other Economic Plants from Pollen

Palynologists managing large reference collections that include pollenfrom many economic taxa are agreed that pollen from domesticates likemanioc and Cucurbita are identifiable on the basis of both morphology andsize (Herrera and Urrego, 1996; Colinvaux et al, 1998; E. Moreno and J.Jones, personal communication, 1998). Maize pollen is much larger thanmost other grasses, including bamboos of the tropical forest (Salgado-Labouriau and Rinaldi, 1990; E. Moreno, P. De Oliveira, and M.B. Bush,personal communication, 1998). Identification of maize in its Mesoamericanhomeland must proceed with caution because teosinte pollen is sometimesas large. Even so, grass pollen measuring 95 microns or more is almostcertainly maize, no matter from where. The investigators cited previouslybelieve they can also identify the pollen of Capsicum (chile pepper), Gos-sypium (cotton), Spondias (hog plum), and Theobroma bicolor (cacao).Caution is still called for in regions where these plants were originallybrought under cultivation. The identifications of domesticated manioc,maize, and Cucurbita pollen in preceramic-age (ca. 7000 B.P.-4800 B.P.)paleoecological and archaeological contexts from Belize, Panama, the Co-lombian Amazon and middle Cauca Valley, northern Peru, and the Ecua-dorian Amazon seem secure (Bush et al, 1989; Mora et al., 1991; Pohl etal., 1996; Monsalve, 1985; Piperno and Pearsall, 1998b, p. 207).

NEW TECHNIQUES: STARCH GRAIN ANALYSIS

Background

A cardinal feature of American agriculture is the large number ofplants that were taken under cultivation and domesticated for their starch-rich underground organs. These plants have been largely blind in paleoeth-nobotanical records from the humid tropics, seriously hindering attemptsto understand the history of tropical forest food production. The analysisof starch grains may help us out of this problem. Starch grain analysis hasbeen well used by Donald Ugent and associates over the years to documentor confirm the identity of various tubers preserved at prehistoric sites onthe arid Peruvian coast (Ugent et al., 1984, 1986). However, starch grainstudies have recently found their first applications in the low and humid


regions of the New World tropics. Here, as with phytolith studies, theanalysis is predicated on the notion that when the macrostructures of tubersdecay, some of the starch grains they contain survive in a largely unalteredstate and are retrievable for study. Because starch analysis is probably aless-familiar method to many archaeologists, a brief review of some basicaspects of the technique is necessary here.

Starch Production, Morphology, and Other Properties

Starch grains, which are found in large quantities in most higher plants,are the major form in which plants store their carbohydrates, or energy(Sivak and Preiss, 1998). They can be found in all organs of a higher plant,including roots, rhizomes, tubers, leaves, fruits, and flowers. However, onlysubterranean organs and seeds commonly make what is called reserve starch,which is differentiated from another starch called chloroplast or transitorystarch. The latter type is principally formed in leaves and other vegetativestructures and also can be found in pollen (Reichert, 1913; Shannon andGarwood, 1984). An important difference between chloroplast and reservestarch is that transitory starch granules do not have the taxon-specific shapesassociated with reserve starch granules. Also, transitory starch, as its namesuggests, is formed during the day and utilized at night, whereas reservestarch is stored to be utilized later in the cycle of the plant. Therefore, itis the reserve starch, formed in tiny organdies called amyloplasts, that ismost useful for archaeological study.

There is a large literature on starch grain properties and morphologythat researchers interested in archaeological applications can refer to(e.g., Reichert, 1913; Whistler et al, 1984; Sivak and Preiss, 1998). Anynumber of atlases and keys of starch grains exist, among the most extensiveof which are Reichert's (1913) and Seidemann's (1966), which containdescriptions and photographs of starch from hundreds of economicallyimportant tropical and other plants. A dedicated starch journal, Die Starke,also exists.

Researchers agree that starch grains are often highly diagnostic ofindividual taxa. For example, Snyder (1984, p. 662) states: "Most of thecommon starches are readily and unequivocally identifiable under a polariz-ing microscope, using the criteria of granule size and shape, form andposition (centric or eccentric) of the hilum (the botanical center of thegranule), and brilliance of the interference cross under polarized light."The surface decoration of the granule (e.g., lamella visible or not visible)also provides identification criteria (Piperno and Hoist, 1998). Althoughthere is a large corpus of literature on starch grain morphology, most of it

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has been compiled by researchers interested in the purely botanical aspectsand commercial uses of starches. They understandably paid little attentionto how grain size and morphology in domesticated crops might differ fromthose in closely related wild species. This will become an area of intenseinterest for paleoethnobotanists.

Based on a reference collection we have accumulated of more than100 species of economically important Neotropical species (Piperno andHoist, 1998, unpublished data) and its comparison with the literature refer-enced previously, the following points can be made about starch identifica-tion in the Neotropical archaeological record: (1) maize, manioc, arrowroot,sweet potato (Ipomoea batatas), achira, yams, yautia (Xanthosoma sagitti-folium), squash, legumes (Fabaceae), and palms can be easily differentiatedfrom each other and from other plants represented in our modern collection;(2) there is significant potential for a precise identification of squashes,maize, achira, and arrowroot, for individual genera of legumes, includingPhaseolus and Arachis (peanuts), and for some individual species of yams;(3) the specificity of manioc grains needs to be determined, but they aredifferentiable from other plants currently represented in our collection aswell as those documented by other researchers—in other words, maniocstarch is not of a common design; (4) there appear to be differences inmaize starch from individual races that may correspond in some way toendosperm type; and (5) tree fruits such as avocado (Persea americana),many palms, mamey (Mammea americana), and soursop (Annona spp.) areunlikely to provide informative data because they largely contain oils, notstarch (palm trunks are obvious exceptions—the starch in these is in needof study).

The properties of starch grains and their sensitivity to degradationunder various conditions are fairly well understood and can be summarizedas follows. Starch grain molecules are primarily composed of amylose oramylopectin; many grains are mixtures of the two. They are highly sensitiveto heat, strong acids and bases, and oxidizing compounds. Many grainsstart to geletinize, whereby they melt and lose their diagnostic properties,at temperatures of between 40° and 50°C. This means that they probablywill not be identifiable residues of archaeological ceramics (unless the potshad a storage function), although this question needs study. A finding ofeven a few manioc-type grains on the ceramic "griddles" retrieved fromarchaeological sites throughout eastern South America, which many investi-gators think were used to bake bitter manioc cakes (e.g., Roosevelt, 1980),would be enough to strongly suggest manioc presence on these artifacts,and at the same time unequivocally rule out other tuber crops, palms,maize, legumes, and various other plants that might have been consumedat the site.


Starch grains can gelatinize at lower temperatures under alkaline condi-tions. Hence, their resistence to destruction in shell middens and otherarchaeological contexts of high pH is in need of study. They often losetheir characteristic extinction crosses under polarized light when desiccated,but this is a process reversible by rehydrating them. The degree to whichstarch from different species may differentially survive in the varying con-texts associated with human settlement (alkaline shell middens, leachedand acidic sediments, locations near the heat of hearths) is unknown.

Starch on Stone Tools, in Archaeological Sediments, and InsideHuman Teeth

The number of starch grain studies carried out to date in the humidNeotropics is limited, but results are promising. Piperno and Hoist (reportedin Piperno and Pearsall, 1998b, pg. 200) isolated grains from the surfaceof grinding stones from an early Holocene age site in the Upper CaucaValley, Colombia (Gnecco and Mora, 1997). A variety of taxa were repre-sented, including arrowroot, legumes, and grasses. Grinding stones andgrinding stone bases from late preceramic and early ceramic contexts (ca.7000 B.P.-3000 B.P.) in Central Pacific Panama similarly yielded grainsfrom a variety of plants, including arrowroot, yams (probably not D. trifida,the major domesticated yam), and legumes, in addition to grains that inmorphology and size were indistinguishable from modern varieties of maizeand manioc (Piperno and Hoist, 1998). The latter two types of starch grainswere recovered from secure late preceramic contexts (7000 B.P.-5000 B.P.).The starch analysis supported the previously obtained archaeobotanicaland paleoecological data in indicating an early development of agriculturein central Panama.

The tools that yielded the highest number of starch grains in our studieswere typically those that contained small interstitial cracks and crevicesthat could be sampled with a fine needle. Presumably, these tiny fissureson the tools were places in which the grains lodged and then were protectedfrom the effects of the humid climate over time.

Cummings and Magennis (1997) found maizelike starch grains inMayan teeth calculi, where it was the most abundant remain present. Possi-ble manioc grains were also present on the teeth. Food residue of varioustypes found in tooth calculi, although not commonly studied at present,have considerable potential for the elucidation of dietary trends in the Neo-tropics.

A very recent development has been the successful isolation of starchgrains from archaeological sediments (Piperno and Hoist, unpublished

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data). These include the sediments that were adhering directly to grindingstones, as well as samples taken from features and profiled walls. Starch,like phytoliths and pollen, can be floated out of sediments from the humidtropics using heavy liquids (Therin et al., 1998). The number of grains isnot astoundingly large, but sample sizes of 50 and more starch grains froma 15cc volume of soil are common. This means that out of the tens ofthousands of grains that were deposited into sites where people commonlyused rhizomes and tubers, a few are surviving, but these few retain thecharacteristics, including the extinction cross, necessary to make positiveidentifications of plants and meaningful measurements of grain size. Starchresearch is just starting in the humid Neotropics, but its potential is clear.

OLD AND NEW CONTROVERSIES

The Neotropics is probably the most contentious area in which micro-fossil techniques are being applied to archaeological subsistence reconstruc-tion. Debates concerning New World agricultural origins, particularly aboutmaize history and the place of tropical forest cultures in the beginnings ofthe domestication process, have a long and rancorous history. The injectionof data from a new technique, phytolith analysis, that indicated people ofthe lowland tropical forest developed and dispersed domesticated plants,including maize, at an early date (Pearsall, 1978; Piperno, 1988; Piperno etal., 1991) did little to quell the unrest. Predictably, then, many of thedisagreements about the use of microfossils in subsistence reconstructionhave centered around the author's and Pearsall's belief that maize phytolithscan be identified in the archaeological records of the Neotropics.

The phytolith (and pollen) evidence for the use of maize in southernCentral America and northern South America between about 7000 B.P.and 5000 B.P., summarized in Pearsall and Piperno (1990) and Pipernoand Pearsall (1998b), is controversial because it conflicts with the knownevidence from macrobotanical remains and with isotopic measurements onhuman skeletons. However, these differences are probably more apparentthan real, because the various lines of evidence have very different levelsof visibility. Carbonized macrobotanical and human skeletal remains arevery poorly preserved in pre-3000 B.P. sites from the Neotropics, and boneisotope data are most useful for assessing the status of maize as a staplecrop, consumed on a regular basis. One wonders what bone isotope recordswould look like from modern tropical forest peoples who consume maizein fermented beverages a few times a month during ceremonial and ritualactivities. Maize was dispersed quickly through the tropical forest after itwas taken under cultivation possibly because it became highly desired as


a feasting beverage. This is not the forum in which to discuss such a scenarioin detail, but investigations of early maize should consider the culturalcontext in which it was used.

Having identified and measured thousands of modern and archaeologi-cal grass phytoliths and completed the additional work on maize discrimina-tion just described, I am convinced that cross-shaped phytoliths provide areliable means for maize identification, with the caveats as noted previously.My desire is to move on and study other important problems, not least ofwhich is the history of the root and tuber crop complex of the Neotropicalforest. Because the phytolith record likely will continue to provide much ofthe primary empirical data on early maize movements through the tropicalforest, I offer the following comments about some criticisms that have beendirected at maize phytolith identification.

Three researchers have expressed serious reservations about thePearsall/Piperno approach to maize identification: Doolittle and Frederick(1991) and Rovner (1996) (also Rovner, 1990 and Rovner and Russ, 1992).It is clear from Doolittle and Frederick's (1991) paper that they had verylittle practical experience with phytoliths before starting their research.They attempted to determine the diagnostic potential of maize phytolithsfrom the American southwest using the Pearsall/Pearsall cross-body crite-ria; reported that in the leaves of four modern races of maize from theregion they could find no cross-bodies; claimed that they, therefore, couldnot carry out the intended study; and then made from this nonstudy sweep-ing conclusions asserting the problematic nature of phytolith research in thesouthwest United States and elsewhere. However, the phytolith drawings intheir Fig. 1 demonstrate that they did isolate many cross-bodies from maize(even with the use of a more restricted definition of cross-shaped phytolithpreferred by Mulholland, 1993), and could not recognize them. Doolittleand Frederick (1991) also claimed that: (1) teosinte and maize phytolithscould not be differentiated, citing not empirical data they or anyone elsegenerated, but a personal communication from a botanist who has neverstudied phytoliths; (2) cross-shaped phytoliths of different sizes were beingdifferentially preserved in sites, using a study of Pleistocene-aged geologicsediments in which no cross-bodies and very few phytoliths of any kindwere present (differential preservation is highly unlikely because all aresolid plugs of silica, and many smaller cross-bodies have been recoveredfrom pre-maize contexts in Latin America); and (3) that phytoliths of alltypes were of limited taxonomic value, citing a single study in which theresearcher involved (Metcalfe, 1971) actually stressed the taxonomic poten-tial of the phytoliths being studied (Cyperaceae).

Doolittle is a well-known investigator who has carried out importantstudies dealing with agricultural evolution, but who was obviously ill-

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acquainted with phytolith research at the time of his analysis. Surprising,in addition to the numerous factual errors in the article, is the aggressivenessof its tone. It is as if the goal of the study was to refute rather than evaluatethe idea that maize phytoliths could be identified. The phytolith communitystill awaits a legitimate study of maize in the southwest United States.

Rovner's criticisms of our use of cross-bodies in maize identificationhave to do with the following points: (1) Pearsall's (1978) definition of across-shaped phytolith, which used such attributes as indentation numberand length to clearly demarcate them from other phytoliths in grass leavescalled bilobates, is rigid and arbitrary, goes far beyond definitions made byearlier phytolith researchers, and does not capture a segregated set ofphytoliths; (2) phytolith descriptions and measurements made with conven-tional techniques (an eyepiece micrometer and a microscope) are inferiorto those made with the assistance of computer-assisted image analysis; (3)variability in phytolith size of a single species caused by local environmentalconditions poses significant problems; and (4) phytolith researchers haveproblems identifying the cross-body three-dimensional variants I described.Points one and two have been answered by Piperno (1992), Pearsall (re-ported in Piperno and Pearsall, 1993b), and Piperno and Pearsall (1993a).To these comments, I add the following.

Rovner (e.g., Rovner and Russ, 1992; Rovner, 1996) claims that com-puter-assisted image analysis (CAIA) is a superior technique for maize andother phytolith description and identification. However, he has not carriedout the extensive studies of phytoliths in modern plants and archaeologicalsediments needed to test the approach. In CAIA, phytolith images arecaptured by the computer, which then makes a variety of measurementsof size and shape. CAIA cannot adequately describe three-dimensionalstructures of particles because it makes measurements in only two dimen-sions, and for this reason it performed poorly in discriminating wild grassesfrom maize when Pearsall compared it with conventional microscopy (inPiperno and Pearsall, 1993b). Pearsall also demonstrated that phytolithmeasurements made with the eyepiece micrometer, importantly includingall of the different cross-body variants (Fig. 21), were as accurate as thosemade with the help of the computer. She found that measuring one typeof phytolith was no faster using the computer system than using an eye-piece micrometer.

Rovner's single published CAIA study that dealt with a Neotropicalarchaeological problem and plants (Russ and Rovner, 1989) compared asmall number of phytoliths in three races of maize and two races of teosinte.The limited number of phytoliths and taxa studied resulted in erroneousconclusions concerning the diagnostic potential of phytolith size in anothergrass type, the bilobate, in maize discrimination (see Piperno and Pearsall,


Fig. 21. Top center and bottom, three cross-shaped phytoliths enclosed in the leaf epidermisof maize. The two Variant 1 cross-bodies at the bottom are wider than the Variant 6 cross-body at the top. This difference in the size of different cross-body variants typifies maize andother grasses, and also contributes to accurate identification archaeologically.

1993a, pp. 348-350). Russ and Rovner (1989), like Pearsall, did not findany unique characteristics of maize phytoliths using CAIA parameters.CAIA has shown some promise, and may be especially useful for quicklymeasuring and quantifying a restricted range of phytoliths in a large dataset. The degree to which it might improve current phytolith classificationsystems, and whether it can effectively and routinely identify phytoliths inlarge and diverse archaeological and paleoecological assemblages as doesconventional microscopy, is unknown. It is unnecessary for many taxo-nomic problems.

Concerning Rovner's third point, there undoubtedly is some variationin phytolith size of a single species that is caused, in part, by local environ-mental conditions (Piperno, 1988). Infraspecific variability is always thecase for morphologic traits, be they from phytoliths, pollen, or seeds. Paly-nologists have shown that average infraspecific pollen size in wild grasses

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can vary by 10 to 15% (E. Moreno, personal communication, 1998). Thereal question is, does this variability conflate interspecific comparisons? Theanswer with regard to wild grass phytolith size and maize seems to be no.

For example, infraspecific variability in the wild grass cross-bodiesreplicated by Piperno (1988, pp. 75-79), to which Rovner (1996) refers asa demonstration of problematic and uncontrolled variation, is actually quitelimited. A Mexican population of a wild grass, Hymenache amplexicaulis,had a mean cross-body width of 11.7 micrometers, compared with meanwidths ranging between 10.5 and 11.3 micrometers for cross-bodies fromfour populations from Panama (Piperno, 1988, p. 76). The Mexican replicatefalls outside of the range for Panamanian grasses, as Rovner (1996) notes,but by only 0.4 micrometers, which amounts to a difference of 4%. Moreto the point, cross-bodies from all five populations of this species are small,and all are significantly smaller than those of maize.

This pattern, in which infraspecific variation in wild grass cross-bodysize was unremarkable, and in which cross-bodies were separable fromthose of maize, or not, characterized my replicate study. In a Belizeanpopulation of a wild grass, Cenchrus echinatus, mean cross-body width was15.1 micrometers, which is 8% larger than the maximum value for meanwidth in three Panamanian populations (range: 13.3-14.0 micrometers). Itwas obvious from the initial studies of this grass (Piperno, 1984) that it wasunusual among wild species in that it produced cross-bodies as large asmaize (mean cross-body size in Latin American races of maize usuallyvaries between 12.8 and 15.9 micrometers) (Piperno, 1988, p. 74). The factthat a Belizean population produces even larger phytoliths than Panama-nian populations does not indicate that environmental variables inflict chaoson its size distributions, but rather that the cross-bodies are large, no matterwhere they grow. Cross-body three-dimensional morphology is needed toseparate C. echinatus from maize, which it does quite effectively (Piperno,1988, pp. 68-79). In the replicate study, cross-body morphology of the wildgrasses was also consistent (Piperno, 1988, p. 76).

Additional studies of infraspecific phytolith variability were carriedout by the author as part of the large analysis of maize and wild grassphytoliths described previously. Three different populations of one of thewild grasses with cross-bodies as large as maize, Maclurolyra tecta,contributed Variant 1 cross-bodies with mean widths of 16.7, 15.6, and13.8 micrometers. Simply put, these phytoliths, like those of C. echinatus,are large. Replicates of wild grasses that did not present size problemsfor maize identification all produced small cross-bodies (D. R. Piperno,unpublished data). Contra Rovner's claims, these data indicate thatphytolith size variability in wild species is not problematic for maizephytolith identification.


I can find no basis for Rovner's claim that my identification of differentthree-dimensional cross-body forms is coming under serious criticism fromphytolith researchers. There is no doubt that these forms actually exist andare not artificial creations of conventional microscopy, as Rovner (1996)argues (see Fig. 21 and SEM and other illustrations in Piperno, 1988, pp.228-231, and Piperno and Pearsall, 1998a). Calderon and Soderstrom (1973,p. 30) noticed the bamboo-specific Variant 8 cross-bodies in epidermal thinsections of the aforementioned species Maclurolyra tecta (and also notedthat they were large), but because the phytoliths were partially obscuredby enclosing plant tissue they could not describe them very well and calledthem "modified and oryzoid" cross-bodies. Other cross-body variants areconsistently illustrated in large studies of grass phytoliths (e.g., Brown,1984; Figueiredo and Handro, 1971). Raising and lowering the focal planeof the microscope, by which Rovner means focusing in and out on thephytolith, could certainly make the top of a phytolith clearer than thebottom, or vice versa, but how can three-dimensional or any aspect ofphytoliths be studied if the body is not put into clear focus?

A number of published studies have employed the three-dimensionalcriteria without problem (e.g., Mulholland, 1993; Pearsall, 1989; Umlauf,1993). I recently took an informal poll of others who have studied cross-bodies and asked them whether they had difficulty recognizing the differentforms. The response was uniformly negative (J. Jones, L. Kealhofer, Z.Zhao, and Q. Jiang, personal communication, 1998). Where, then, is thetechnique being "widely questioned" (Rovner, 1996, p. 431)? Are some ofthe three-dimensional criteria subtle, and does it take time, practice, anda good reference collection to learn how to recognize all of the them? Yes;identifying phytoliths, like pollen and starch grains, requires studied workand patience, especially where a diverse flora is being investigated.

Finally, what Rovner (1996, pg. 431) calls the "failures" of the maizetechnique (citing studies by Mulholland, 1993, and Umlauf, 1993, and claim-ing that others are being "increasingly reported" from New World sites)actually refers to the fact that in some sites where maize is thought to havebeen consumed or where macro-remains of the plant are present, cross-shaped phytoliths are not well represented or are not large enough to bediscriminated from wild species with a high degree of confidence. Resultssuch as this are commonplace for paleoethnobotanists, who must considertaphonomic as well as taxonomic concerns in their attempts to reconstructancient diet (e.g., Pearsall, 1989). Cross-body presence depends largely onwhether maize leaves [husks also produce cross-bodies, but in much smallernumbers than leaves (Piperno, 1988)] were discarded at a sampling locale.In fact, Mulholland (1993, p. 143), well aware of these taphonomic issues,cited ethnographic evidence that most vegetative material "was never

Piperno432

brought to the village," and that "only the cobs were consistently introducedto the village itself," providing an explanation for the rarity of cross-bodies.She ultimately developed a method to identify cob phytoliths, which werequite common in the site's sediments, and concluded (p. 145) that the cross-body data "corresponds to the ethnographic pattern reported" for theculture. No failure is detectable here.

As I commented in the Phytolitharien Newsletter (Piperno, 1992), ifcurrent maize identification procedures were resulting in the misidentifica-tion of wild grasses as maize, or a persistent inability to recognize maizecross-bodies in contexts in which maize leaves were left behind, the follow-ing would not be true of the results to date: (1) maize occurrence at ca.7000 B.P. and after, but not before, in records from southern CentralAmerica and northern South America, despite the abundance of cross-shaped phytoliths at some earlier sites; (2) maize phytolith occurrence inthe same contexts in which maize pollen and maize-like starch grains areidentified (in other words, maize pollen and starch is also consistentlyoccurring between 7000 B.P. and 5000 B.P., but not before in the records);and (3) absence of maize phytoliths in which maize pollen and starch arenot identified (see Piperno and Pearsall, 1998b, for a summary of thisinformation). Maize phytolith procedures obviously cannot identify everyrace of maize that was used prehistorically because variability in this domes-ticated species is high, and some maize races have smaller phytoliths thanothers. Palynology has similar problems.

I urge researchers who are not convinced by the maize phytolith resultsto evaluate other lines of data they may find more compelling (pollen,molecular biology, starch grains) as counterpoint to what I firmly believeis a largely blind and inadequate macrofossil record for early maize in thehumid tropics (see later). Eventually, a critical mass of data will be assem-bled from the different kinds of evidence being studied, and a consensuson maize origins and early dispersals will emerge. The degree of harmonybetween the phytolith evidence and this consensus may be stronger thanscholars might believe possible now.

Another controversial issue in microfossil studies has been the reluc-tance on the part of some investigators to seriously consider any form ofpollen or phytolith evidence for plant cultivation and domestication becauseof what they perceive to be serious problems with chronological and/ortaxonomic control. Smith (1995a,b) and Fritz (1994,1995) have been partic-ularly vocal in this regard. Associated with their belief that directly datedmacrofossils provide virtually the only acceptable proof for prehistoricagriculture, what Smith (1995b, p. 176) termed the "new standard of evi-dence," was their radical new chronology for the beginnings of farming inthe New World. They proposed that it began during the middle Holocene


(ca. 5000 B.P.) rather than shortly after the termination of the Pleistocene,and that, as in southwest Asia, it was originally undertaken by sedentarysocieties with complex forms of social organization. Their revised age forNew World agricultural origins was based largely on radiocarbon datesobtained on macrofossils of maize and Phaseolus beans from the TehuacanValley in the arid southcentral highlands of Mexico, which scholars agreewas probably not a nuclear area of agricultural development. Althoughtheir new chronology better fit the earliest evidence for agriculture fromthe eastern United States, it was at odds with microfossil data from thelowland tropical forest, where most of the staple crops that supportedindigenous populations at the European contact, including maize, wereoriginally brought under cultivation and domesticated (Sauer, 1950; Pip-erno, 1994b; Piperno and Pearsall, 1998b).

Recent dates on domesticated C. pepo macro-squash remains from theOaxaca Valley, Mexico (Smith 1997), as well as increasing empirical evi-dence from sites located in the tropical lowlands (later; Piperno and Pearsall,1998b), are beginning to make it clear that: (1) plant cultivation and domesti-cation in Mesoamerica and South America occurred shortly after the termi-nation of the Pleistocene, as they did in other pristine areas of agriculturalorigins; (2) lowland tropical forest cultures played crucial roles in thesedevelopments; and (3) models of agricultural origins extrapolated fromsouthwest Asia, where sedentary life and considerable social complexitymay have preceded the onset of cultivation and domestication, cannot beshoehorned into the dramatically different American ecosystem.

The doctrinaire approach to paleoethnobotany advocated by Smithand Fritz that emphasizes macrofossils to the virtual exclusion of allother evidence is particularly unsuited to the humid tropics, becausemany seeds and roots simply do not survive for very long, even aftercarbonization, under the humid environments, alternating conditions ofdrying and wetting, and dense, clayey depositional contexts typical ofthe tropical lowlands (Piperno and Pearsall, 1998b, pp. 32-34). Seeingthe results from the screening and flotation of gallons of archaeologicalsediment from Panama and elsewhere, which typically yielded smallquantities of a few types of hard seeds and nuts, convinces the authorthat preservation often is just too poor to provide cogent reconstructionsof plant use, and that the older the sites are, the worse the preservationis. Pearsall (in Piperno and Pearsall, 1998b, pp. 33-34) demonstrated asharp drop-off in the quantity of macrofossils through time even in anEcuadorean site occupied during the past 3000 years. The root cropsthat were so essential to tropical forest subsistence obviously are notopen to study with macrofossils except under the very best preservationalconditions, such as are found in tropical deserts.

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It seems that the key to reconstructing early plant use in thehumid tropics will be microfossil evidence from both archaeological andpaleoecological contexts. Next, I discuss in more detail the aspect ofthis evidence that has most troubled some investigators: determining thedates of phytoliths and pollen grains recovered from ancient sites.

DEVELOPING RELIABLE CHRONOLOGIESFOR MICROFOSSIL ASSEMBLAGES

With the important development of AMS dating, which made it possi-ble to determine the age of single seeds or small, vegetal fragments recov-ered from archaeological sites, came the uneasy feeling on the part of someinvestigators, discussed in part earlier, that because microfossils could notbe dated in the same manner, one could never be certain that an associateddate for a phytolith or pollen assemblage was the true age of the plantsrepresented in them. Although concerns about the stratigraphic integrityof plant remains are paramount, the chronology of every remain, be it ofmacro- or micro-type, should not automatically become subject to seriousquestion without a close consideration of the specific context in which itwas found. For example, dry caves are notorious for subjecting botanicalmaterials to significant vertical movement because uncharred food remainsare potential foods for burrowing or commensal animals [although a ca.9000 B.P. age for the domesticated Cucurbita pepo recovered from earlyHolocene strata at Guila Naquitz has been confirmed with AMS dating(Smith, 1997)]. In contrast, the dense clays of humid tropical sites areprobably much less prone to such admixture.

Microfossil assemblages that demonstrate persistent trends throughtime (e.g., increase of Cucurbita phytolith size, presence of phytoliths andpollen typical of more primitive maize races and other cultigens in earlierbut not later strata) likely contain few to no intrusive particles from morerecent occupations of sites. Single-component sites are inherently unlikelyto contain plant remains from occupations that occurred later in time.Remains of plants directly recovered from stone tools may confidently bedated by association with the age of the tool because large artifacts arenot expected to have moved downward in sediments after their depositionif no other disturbances are evident in the sediments.

Turning to paleoecological contexts, small bits of sediment containingpollen and phytoliths sampled from tropical lake cores have been shownby numerous studies to provide a reliable context for dating (Colinvaux etal., 1996a, b, Piperno and Pearsall, 1998b). Bioturbation is inherently un-likely due to the rarity of organisms that promote sediment mixing in


anoxic conditions. X-ray and visual analyses of core sections are capable ofrevealing precise details of sedimentation, such as fine, undistorted laminae.When present, such details indicate continuous and undisturbed sedimenta-tion. A series of internally consistent 14-C determinations on sedimentssampled at close and regular intervals from the cores adds to the likelihoodthat sedimentation was indeed undisturbed.

Lakes located in regions with limestone substrates, where ancient geo-logic carbon is introduced into lake water causing anomalous 14-C determi-nations, or situations in which deep root penetration occurs, as happens inmangrove swamps, should be approached cautiously. It is true that agedeterminations from lake cores cannot provide as precise an estimate foragricultural activity as a date on a domesticated seed, but knowing withina few hundred years when significant land clearance signaling agricultureoccurred obviously is important information.

These comments are unlikely to satisfy those who insist on havingdirectly dated macrofossils as proof of domestication and agriculture, buteven the most hardened microfossil skeptic can now rest easier in light ofdemonstrations that it is possible to directly date phytoliths and pollenfrom archaeological and paleoecological sites. When phytoliths form inplant cells, some of the organic material of the cell becomes trapped insidethe phytolith and it remains there over long periods of time. Because thecarbon is locked within the phytolith, it is immune from the various modesof postdepositional contamination. Dating a single phytolith is obviouslyimpossible, so a phytolith assemblage isolated from a discrete sedimentcontext becomes the basis of the analysis.

Wilding (1967) first showed that it was possible to radiocarbon-datephytoliths, and he provided the chemical and physical analyses of the carboninside them needed to show that derived 14-C dates were meaningful. Forexample, it was demonstrated that this carbon was organic in origin, thatit was impervious to a strong oxidation treatment, and that such a treatmentremoved the extraneous carbon clinging to the outside of phytoliths thatwas a potential contaminant (Wilding et al, 1967). Dating phytoliths didnot become commonplace because many hundreds of grams of sedimenthad to be processed when conventional beta decay counters were the onlymeans available to determine an age. With the advent of AMS dating, onlya handful of phytolith-rich sediment, about 35-45 g, usually provides a 1-3milligram amount of carbon sufficient for an age determination. A methodto process archaeological sediment samples for AMS phytolith dating isprovided by Mulholland and Prior (1993).

It should be noted that stable carbon isotope (12-C/13-C) values canalso be calculated directly from phytoliths as part of the routine procedureused to date them (C. Prior, personal communication, 1998). More basicresearch is needed in the tropics to explore the precise relationship between

Piperno436

delta 13-C values derived from phytoliths and from whole vegetative struc-tures of the same plant, but results so far from the temperate zone indicatethat phytolith-stable carbon isotope values provide significant informationon whether primarily C3 or C4 plants contributed the phytoliths in soilassemblages (Kelly et al., 1991; Fredlund, 1993). Such an approach appliedto phytoliths from lake sediments may be particularly useful in assessinghow the changes in the seasonality of annual precipitation and temperatureduring the Pleistocene to Holocene transition, which are strongly predictedby climatic modeling, may have affected the photosynthetic pathways andgrowth habits (perennial vs. annual) of plants that soon after were broughtunder systematic cultivation and domesticated.

There are currently a small number of phytolith dates available fromarchaeological contexts. However, they strongly support the viability of thetechnique in the Neotropics because they accord well with dates fromassociated cultural materials such as charcoal, shell, and human bone(Piperno and Pearsall, 1998b, Chapter 4). Also, when insufficient dateablematerial is recovered from particular occupational phases of sites, asoften happens with the earliest habitations, phytoliths provide a handymedium for chronological assessment because they are often well pre-served in the most ancient strata (Piperno and Pearsall, 1988b, pp.214-216). In the case of the early Holocene site Vegas, located in southwestEcuador, a close correspondence was found between the age of phytolithassemblages and the size of the Cucurbita phytoliths isolated from them.Phytolith sizes and ages indicate that wild Cucurbita spp. were being ex-ploited during the terminal Pleistocene and earliest Holocene, and that adomesticated species was present by 9060 B.P. (Piperno and Pearsall, 1998b,pp. 186-197; Piperno et al, 1998).

The possibility of directly dating pollen grains has been discussed bypalynologists for some time, and the 1990s witnessed successful applicationsin lake sediments (Long et al., 1992; Goman and Byrne, 1998). Techniquesbeing developed minimize the amount of extraneous organic matter recov-ered along with pollen from lake cores, like cellulose, and ensure that agedeterminations are based on an almost pure extract of pollen (Prior, 1998).It also seems possible to separate pollen grains from individual taxa fordating by means of density gradients (Prior, 1998). Such an approach maybe especially applicable to cultivar taxa (e.g., Cucurbita, Zea mays, Mani-hot), which often are much larger, and, hence, more carbon-rich than others.Preliminary studies have shown that C-14 dates derived directly from pollenclosely agree with the associated C-14 ages from the core's bulk sediments,indicating that reliable pollen chronologies are being generated (and alsothat the sediment is not much older or younger than the pollen it contains)(Prior, 1998). Only a 1-cm pollen-rich segment of a core is needed to providea sufficient quantity of pollen for an AMS date (Prior, 1998).


The routine AMS dating of phytolith and pollen assemblages fromarchaeological and paleoecological contexts that now seems possible shoulddramatically improve the confidence in the results derived from microfossilstudies. The likelihood that sufficient starch residue can sometimes beretrieved from archaeological sediment for an AMS date appears to behigh. This raises the prospect of having three different classes of microfossildata from a single sediment context, all independently dated by radio-carbon.

SUMMARY

What Have Microfossil Approaches Told Us About Ancient Plant Useand Domestication in the American Tropical Forest, and What Can We

Expect to Learn?

This paper attempts to identify the crop plants and general subsistenceand paleoenvironmental problems that can be studied with the phytolith,pollen, and starch records in the Neotropics. The complementary natureof these microfossils deserves to be repeatedly stressed. Where one or twoof them are weak, as in detection of root crops by pollen and phytoliths,another is strong. Pollen will never tell us if teosinte seeds were regularlyexploited and then manipulated into maize cobs. Phytoliths can becausefemale reproductive structures produce highly diagnostic forms. Paleoeco-logical studies have already found substantially improved precision by usingphytoliths and pollen in tandem because the strengths and shortcomingsof one technique in identifying individual taxa of the tropical forest anddifferent scales of human disturbance are often offset by the other (Piperno,1993). Table III presents a summary of the expected visibility of majoreconomic taxa of the lowland Neotropical forest in microfossil records.

It is far too early to attempt a transtropical comparison of subsistenceand dietary trends because few sites dating to before 3000 B.P. have beeninvestigated, particularly in Mesoamerica. However, there are sufficientdata from southern Central America and northern South America to iden-tify and evaluate the following patterns.

First, a variety of tropical forest tubers, herbaceous seed plants, andtree fruits are present in archaeological pollen, phytolith, and starch assem-blages from early Holocene (ca. 10,000 B.P.-8000 B.P.) contexts in theUpper and Middle Cauca valleys, Colombia, Amazonian Colombia, andcentral Panama (Herrera et al, 1992; Cavelier et al., 1995; Gnecco andMora, 1997; Piperno and Pearsall, 1998b, pp. 182-227). The Upper CaucaValley evidence indicates that people were already developing close rela-

Piperno438

tionships with the tropical forest flora and processing tubers and a varietyof other plants, including legumes, for food during the earliest Holocene (byor shortly after 10,000 B.P.). A critical question, in view of the dramaticallydifferent ice age environments and (probably) resources that the ancestorsof some of these people were exploiting before the Holocene began, iswhen such close relationships began to be formed. Few late and terminalPleistocene sites have so far been studied, but arriving at some understand-ing of pre-Holocene plant subsistence is obviously of fundamental impor-tance.

Second, Cucurbita phytoliths are present in early Holocene contexts(ca. 10,000 B.P.-8000 B.P.) from archaeological sites in central Panama,the Upper Cauca Valley, Colombia, southwest Ecuador, and the ColombianAmazon (Piperno and Pearsall, 1998b, pp. 186-217; Piperno et al, 1998;D. R. Piperno, unpublished data). Cucurbita phytoliths from the latter two


Table III. Projected Levels of Visibility of Some Crop and Other EconomicallyImportant Plants in Tropical Plant Microfossil Records Based on Present Knowledge

of Production, Taxonomic Specificity, and Survival in Sediments

Plant

TubersManihot esculenta (manioc)Ipomoea batatas (sweet potato)Dioscorea spp. (yams)Xanhossoma sagittifolium (yautia)Canna edulis (achira)Calathea allouia (leren)Maranta arundinacea (arrowroot)

LegumesPhaseolus spp. (beans)Arachis hypogaea (peanuts)Canavalia spp. (jackbeans)

Cereals and vegetablesZea mays (maize)Cucurbita spp. (squash)

Tree fruitsPalmae (palms)Persea americana (avocado)

Phytoliths

0000122

000

22

20

Pollen

1"000000

000

10

1'0

Starch

21?b

21?b,c

2

1?b

2

2?1?

9

2??''

0

Note: 0 = low probability of recovery; 1 = fair probability of recovery; 2 = goodprobability of recovery.aManioc pollen is probably most visible in sediments recovered from formerfield areas.

bTubers and other plants that were not processed before being eaten may have lessvisibility, since starch recovery will have to be from sediment.

c Yautia starch may be identifiable but the grains are tiny and many will have tobe recovered.

dCucurbita starch seems diagnostic but survivability in sediment is unknown.eSome palms have diagnostic pollen, but recovery is often poor.

areas have sizes indicating domestication by 9080 ± 60 B.P. and8090 ± 60 B.P., respectively, each date representing a direct AMS phytolithdetermination on the phytolith assemblage (Piperno and Pearsall, 1998b,pp. 188-197, 203-205; Piperno et al., 1998). Phytolith dates for the first twoearly squash contexts are forthcoming, but phytolith assemblages with datesof 5560 ± 80 B.P. and 6910 ± 60 B.P. occur stratigraphically above theearliest Panamanian Cucurbita remains (Piperno and Pearsall, 1998b, pp.213-217). The Ecuadorian sequence is most clear in indicating the localpresence and exploitation of a wild gourd during the terminal Pleistoceneand early Holocene periods and its subsequent domestication by ca. 9000B.P., whereas the Amazonian Colombian and possibly, Panamanian se-quence indicate an introduction of a domesticated form of Cucurbita byca. 8000 B.P. The Upper Cauca Valley context for Cucurbita possiblydoes not date much later than 9500 B.P., and there, like in the terminalPleistocene/early Holocene Ecuadorean context, phytoliths have sizes typi-cal of modern wild gourds (D.R. Piperno, unpublished data).

It is almost certainly not coincidental that the earliest domesticatedC. pepo squash remains from Guila Naquitz cave in Mexico (Smith, 1997)date to about the same time as the domesticated Cucurbita phytoliths atVegas. Cucurbita species appear to have been among the earliest plantsbrought under cultivation and domesticated in both Mesoamerica and SouthAmerica. Archaeological deposits that date to after ca. 7000 B.P. generallycontain few to no Cucurbita phytoliths, an expected result if early Holocenedomestication occurred because many modern domesticated populationsdo not produce them.

Third, two now-minor root crops, leren and arrowroot, are consistentlypresent in the archaeological phytolith assemblages that were directly datedto between 9000 B.P. and 7000 B.P. from southwest Ecuador, Panama, andAmazonian Colombia discussed previously (Piperno and Pearsall, 1998b,pp. 182-227). These data are in accord with the notion that pre-7000 B.P.food production systems were characterized by a simple kind of horticulturepracticed largely in house gardens (no significant clearing of the forest forlarger-scale agricultural plots yet). Paleoecological data from Panama andelsewhere support this notion (Piperno et al, 1991 and later this chapter).

Fourth, manioc pollen and starch grains that compare favorably withmanioc are present in sites in Belize, Panama, and the Colombian Amazondating to between ca. 7000 B.P. and 4750 B.P. The starch grains were foundon grinding stone tools from Central Panama that occurred in secure latepreceramic (ca. 7000 B.P.-5000 B.P.) contexts, and where associated phytol-ith assemblages discussed previously yielded direct AMS dates of 6910 B.P.and 5560 B.P. (Piperno and Pearsall, 1998b, pp. 209-227; Piperno andHoist, 1998). Manioc pollen occurred in sediment cores from Belize and

440 Piperno

Amazonia Colombia that likely penetrated former fields. The Colombianmanioc occurred 10 cm below a 2-cm core level with dates of 4330 ± 45B.P. and 4695 ± 40 B.P. (Mora et al, 1991). The Belizean manioc waspresent in two different sites located 50 km apart and was directly associatedwith dates of 4591 B.P. from one site and 4750 B.P. from the other (Pohlet al, 1996). If, as believed, manioc domestication occurred in or near theOrinoco Basin, then even earlier remains should be found in northernSouth America.

Fifth, maize phytoliths, pollen, and/or starch grains are present inarchaeological and paleoecological sediments and/or on stone tools frommany of the same sites in lowland southern Central America and northernSouth America just discussed, in deposits that date to between ca. 7100B.P. and 5000 B.P. (Piperno and Hoist, 1998; Piperno and Pearsall, 1998b).Conversely, pre-7100 B.P. contexts from these sites do not contain microfos-sil remains of maize. This, as several investigators have noted, is earlier thanthe current maize evidence from Mesoamerica (Smith, 1995a,b). However,archaeological data from maize's hearth in the Pacific lowlands of Mesoam-erica are extremely sparse, making comparisons with the chronology ofevents to the south difficult.

Sixth paleoecologic sequences from the middle Cauca Valley, Colom-bia, the Colombian Amazon, the Ecuadorian Amazon, central Panama,Belize, and the Mexican Gulf Coast are consonant in indicating the develop-ment of slash and burn agriculture with maize between 7000 B.P. and 4200B.P. (Monsalve, 1985; Bush et al, 1989; Mora et al, 1991; Piperno et al,1991; Rue, 1987; Pohl et al, 1996; Pope and Pohl, 1998). At present, thisevidence is time transgressive. That is, data from southern Central Americaand northern South America adduce this form of agriculture by between7000 B.P. and 5000 B.P., whereas it is first detectable in sites from Mesoam-erica between ca. 5000 B.P. and 4200 B.P. Again, fewer sites have beenexamined in Mesoamerica, so current trends may be more apparent thanreal. In summary, the evidence from several different regions points stronglyto the development of food production in the lowland tropical forest duringthe early Holocene, and the subsequent emergence of truly productiveslash-and-burn systems 2000 to 3000 years later.

Paleoethnobotany and Explanations of Culture Change

Producers and consumers of paleothnobotanical data alike have com-mented that the subdiscipline of paleoethnobotany has only weakly contrib-uted to general theoretical explanations of culture change (Ford, 1988;Marquardt, 1988; Gardner, 1995). However, with the increasing quality and


quantity of information that is becoming available to them, paleoethnobota-nists are perfectly positioned to actively formulate and structure theoreticaldebates in archaeology. For example, paleoethnobotanical data have sub-stantial potential for testing evolutionary ecological and more strictly selec-tionist evolutionary explanations for agricultural origins (Piperno and Pear-sail, 1998b). Other theoretical constructs for major changes that occurredin prehistoric subsistence and settlement systems, such as risk theory (Win-terhalder and Goland, 1997), can be tested through paleoethnobotany. Theincreasing refinement of the data also means that paleoethnobotanists canbe more innovative in their uses of traditional data sets. For example, bycombining information on the efficiency of food procurement in differentmodern habitats with reconstructions of vegetational history, broad esti-mates can be made of foraging return rates (rates of energy capture) inprehistoric ecosystems through time (Piperno and Pearsall, 1998b). Otheraspects of past environments that must have significantly affected humansubsistence decisions (e.g., changes in the seasonality of precipitation andtemperature) are open to study with microfossils.

The close links between paleoethnobotanical data, subsistence, andpaleoenvironment does not mean that paleoethnobotanists should distancethemselves from explanations of the origins of social complexity. Manyinvestigators of this issue find features such as the presence of highly produc-tive crop plants, food surpluses, and decreasing access to good agriculturalland to be closely connected to social competition and conflict, the hallmarksof cultural complexity, and all these features leave tangible paleoethnobo-tanical evidence (e.g., Cooke and Ranere, 1992; Pohl et al, 1996).

The next decade should bring us to a clearer understanding aboutwhen, why, and how peoples of the lowland tropical forest came to formclose relationships with their complex flora, brought some species undercultivation and domesticated them, and arguably developed effective sys-tems of agriculture earlier than they are presently demonstrable in thecooler and drier regions of the Neotropics. Microfossil studies will likelyform the underpinning for much of this research.

ACKNOWLEDGMENTS

The author's phytolith and starch research was made possible by sup-port from the Smithsonian Tropical Research Institute (STRI) and a grantto the STRI from the Andrew W. Mellon Foundation. The grass silica bodystudies were also supported by a grant to the author and Deborah M.Pearsall from the National Science Foundation (BNS-89-2365). Part of thegrass phytolith research was carried out at the Museum Applied Science

Piperno442

Center for Archaeology (MASCA), University of Pennsylvania, who theauthor thanks for its generous support.

I am indebted to the following people, who for many years have beengood and true colleagues and stimulating collaborators: Mark B. Bush,John Jones, Anthony J. Ranere, Richard Cooke, and Deborah Pearsall.Irene Hoist, Digna Matias, and Enrique Moreno provided excellent techni-cal support for the research conducted in the author's laboratory.

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