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Yucca filamentosa and Yucca flaccida (Agavaceae) Are DistinctTaxa in Their Type LocalitiesAuthor(s): Daniel B. WardSource: Castanea, 77(3):273-279. 2012.Published By: Southern Appalachian Botanical SocietyDOI: http://dx.doi.org/10.2179/10-017URL: http://www.bioone.org/doi/full/10.2179/10-017

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CASTANEA 77(3): 273–279. SEPTEMBER 2012Copyright 2012 Southern Appalachian Botanical Society

Yucca filamentosa and Yucca flaccida(Agavaceae) Are Distinct Taxa in

Their Type LocalitiesDaniel B. Ward*

Department of Botany, University of Florida, Gainesville, Florida 32611

ABSTRACT There has been question whether the taxon known as Yucca filamentosa(Agavaceae) is to be distinguished from the taxon known as Yucca flaccida. Much of theuncertainty lay in the absence of sure knowledge of the forms intended by their originalauthors. A neotype of Y. flaccida from Florida was selected in 2006. Here, the type locality inVirginia of Y. filamentosa is revisited and an epitype is selected. The two taxa, as represented byplants from these two type localities, differ markedly in a number of characteristics. It issuggested that Y. filamentosa and Y. flaccida be retained at specific rank.Key words: Agavaceae, epitype selection, Virginia botany, Yucca filamentosa, Yucca flaccida.

INTRODUCTION In the eastern UnitedStates, the genus Yucca (Agavaceae) is aninfrequent but easily recognized component ofthe flora. Few in number, the species by andlarge are free of taxonomic and nomenclatur-al complexities. Yucca aloifolia L. with its erectstems and stiff, spiny-edged leaves occurs inlocal abundance on the coastal dunes and atwidely scattered sandy locations inland; it wellmerits the common names Spanish-dagger orSpanish-bayonet. Yucca gloriosa L., the Mound-lily Yucca, is now very rare on its nativecoastal dunes; its smooth-edged leaves andshort, often-branched stems form attractiveclumps when in cultivation. A third species—or small group of species—stands apart byhaving stemless basal rosettes and leaves withpartially detached marginal fibers. Theseplants carry the names Yucca filamentosa L.or Yucca flaccida Haw., and are most often justcalled Yucca.The nomenclatural history of the eastern

species of Yucca has been adequately detailedelsewhere (Ward 2006), but no clear taxo-nomic understanding has been reached re-garding the ‘‘Filiferae,’’ those plants withmarginal fibers on the leaves. The group has

been stated to consist of only a single variablespecies, Y. filamentosa (Chapman 1897; Ahles1964, 1968; Wunderlin 1998; Wunderlin andHansen 2003), or two species usually called Y.filamentosa and Y. flaccida (Trelease 1902,Small 1933, Fernald 1944, Dress 1976, Duncanand Kartesz 1981, Clewell 1985, Godfrey 1988,Hess and Robbins 2002, Ward 2004). No fieldstudy has yet been conducted that gives strongevidence for the presence in eastern NorthAmerica of one species, or two.

THE PROBLEM A central impediment tounderstanding the variability of the filiferousyuccas has been uncertainty as to what formof the plant was meant by the authors of thetwo taxa. A scientific name, of course, isunderlain by an actual specimen, the ‘‘type,’’that had been used in composing the originaldescription. Yet neither Yucca filamentosa norYucca flaccida was historically based on anadequate type. Yucca filamentosa was namedand cryptically described by Carl Linnaeus inhis Species Plantarum (1753), but is typifiedonly by his reference to a book, Flora Virginica(1743), published in the Netherlands by hisfriend Jan Frederik Gronovius, and to Grono-vius’ partial specimen—which Linnaeus hadnot seen. And Yucca flaccida was named anddescribed by Adrian Hardy Haworth (1819)

*email address: gordon_c_ward@yahoo.comReceived March 24, 2010; Accepted November 30, 2010.DOI: 10.2179/10-017

273

from plants in his London garden, but no typewas preserved for modern appraisal.When a type of a species is either not

retained or has been lost, the InternationalCode of Botanical Nomenclature (McNeill et al.2006) permits a later person to select areplacement, a neotype, which carries all thepowers of the missing original. Haworth didnot know the source of his Yucca flaccida, buthis description of the leaves as longo-lanceola-tis planis well fits the southeastern plantcommonly given that name. To provide no-menclatural certainty as to what is represent-ed by Haworth’s name, a neotype was selected(Ward 2006) from a population in GilchristCounty, Florida. Duplicates of this neotypehave been widely distributed, and the pub-lished photographs well illustrate the habit ofthe plant.The type of Yucca filamentosa is not so easily

addressed. In this case a type does exist—acuriously incomplete specimen from Virginia.Gronovius had obtained his plant from JohnClayton, the county clerk (an importantposition at that time) and tobacco-plantationowner of the coastal town of Gloucester,Virginia (Berkeley and Berkeley 1963). Clay-ton was interested in the plants he foundaround him and attempted to name themwith the European-oriented books then avail-able. Many of his plants, of course, were not inthese books. To further his efforts, he mountedpressed specimens on large sheets of heavypaper. He then wrote on the sheet an Englishor Latin commentary as to where the plantgrew, its uses, etc., as well as an original Latindescriptive polynomial name. For many of hisspecimens he followed the odd practice ofmounting the plant as though it were arisingfrom a paper drawing of a vase or bowl ortureen pasted over its base.As early as 1735, Clayton began to corre-

spond with and send specimens (perhaps onlyduplicates) to Gronovius in Leiden, Nether-lands. Gronovius, seemingly with Clayton’sacquiescence, and lacking any consequentialcollections from other sources, assembledClayton’s notes and Latin polynomial namesinto a small book, Flora Virginica (1743). Thispublication quickly gained broad acceptanceas a guide to the plants of the NewWorld thenunder exploration and settlement. Gronovius’book reached Linnaeus in Upsala, Sweden,

and the Flora’s many new names and descrip-tions were copied (usually without change,but with credit) into Linnaeus’ own SpeciesPlantarum (1753). But Linnaeus, by an act thatnow seems so obvious but was then quitenovel, added in the margin of his text a singledescriptive word, an epithet. This simplecombination of the generic name followed byan epithet, created the now universally fol-lowed scientific binomial.The Virginia plant that Clayton, and then

Gronovius, named Yucca foliis lanceolatis acu-minatis integerrimis margine filamontosis ("Yuc-ca with lanceolate acuminate entire filament-margined leaves’’) was renamed by Linnaeusas Yucca filamentosa. The specimen behind thisname—which by the modern Code is thetype—still exists, now in the closely guardedpossession of the Natural History Museum,London. It consists of a drawing of anelaborately decorated two-handle vase fromwhich arise two flowering branches of a yuccainflorescence. (This specimen can be viewedon-line [http://www.nhm.ac.uk] or in part inFernald 1944.) No leaves are present; there isthus no suggestion of their distinctive form. Itis apparent that Gronovius was wholly depen-dent upon Clayton’s words for their descrip-tion.Flowers of Yucca filamentosa and Y. flaccida

have been described as differing in sepal/petalsize and shape (Small 1933, Fernald 1944).No contrast is readily apparent between thedried flowers of the Clayton specimen andflowers of living Yucca flaccida. But freshflowers from the Gloucester plants do showdifferences, as noted below.

THE TYPE LOCALITY To determine theform of the plant that Linnaeus had describedso briefly, knowledge was needed of thespecies as it occurs where Clayton had livedand collected. Virginia is a rather well under-stood area botanically, with herbarium collec-tions both within the state and elsewhere(Fernald 1942, 1943). Although specimens ofYucca from coastal areas of the state wereavailable, it was thought essential to see andcollect from the same population sampled byClayton, if that were possible.Initial visits to coastal Virginia and cursory

exploration in and around Gloucester foundYucca gloriosa, although only in cultivation,but no Yucca filamentosa. Then, with the aid of

274 VOL. 77CASTANEA

the local botanists, a generous population of Y.filamentosa was found on the outskirts ofGloucester, in the smaller town of GloucesterPoint.The habitat of Yucca filamentosa as found at

Gloucester Point differs markedly from theopen dunes along the coast and from theoriginally more heavily wooded lands of thepiedmont to the west. Much of the area hasbeen greatly modified by farming and resi-dential housing over the two-and-a-half cen-turies since Clayton’s time. The plant, asstudied here, is present on a small tract ofcut-over woodlands, on sandy loam over whatare probably post-Pleiocene sand hills. Thetract had been partially cleared in an aban-doned effort to prepare it for residentialconstruction. Widely spaced Pinus virginianaMill., ca 25 m in height and 50–60 years inage, was the only remaining tree. Survivingwoody vegetation included: Callicarpa ameri-cana L., Castanea pumila (L.) Mill., Diospyrosvirginiana L., Ilex opaca Ait., Quercus phellos L.,Quercus velutina Lam., and Sassafras albidum(Nutt.) Nees. The vines Parthenocissus quinque-folia (L.) Planch., Smilax bona-nox L., Smilaxrotundifolia L., Vitis aestivalis Michx., VitisrotundifoliaMichx., and the nonnative Lonicerajaponica Thunb., were rampant.

Beneath the tangled second-growth vegeta-tion, plants of Yucca filamentosa were quitenumerous. Many were of flowering age, withold inflorescences. There were also somehundreds of young plants, all of a similar size,indicating a season or two of profuse seedproduction following opening of the canopywith the partial land-clearing.

AN EPITYPE In those cases where theholotype of a new species is so defective as tobe ambiguous and cannot be critically identi-fied for purposes of the precise application ofthe name, the Code (Art. 9.7; McNeill et al.2006) permits a supporting specimen, anepitype, to be selected. Though it is reasonablycertain that plants of Yucca from the vicinity ofGloucester, Virginia, are representative ofYucca filamentosa, this cannot be demonstrat-ed from the incomplete type. Selection of anepitype representing leaves, as is done here, isappropriate. (The following description close-ly parallels that of Y. flaccida [Ward 2006], tofacilitate comparison.)

Yucca filamentosa Linnaeus, Sp. Pl. 1: 319.1753. TYPE: lectotype, Clayton 720 (BM-000051821), designated by Jarvis (2007:931); epitype, selected here, D. B. Ward10773, 25 June 2009. Locally frequent, sandyloam of dry open mixed-deciduous woodland,Hill Road, Gloucester Point, VIRGINIA (FLAS;iso-epitypes, GH, NY, TEX). ¼ Yucca concavaHaworth, Suppl. Plant. Succ. 34. 1819. Leavesbasal, 6–8 cm broad, 50–60 cm long, narrowlyelliptic, deeply (to 1.5 cm) longitudinally andtransversely concave when young, becomingplanar after 2–3 years, rigid (because of 3-dimensional shape), marginal fibers 15–20cm long, overlapping (each lower fiber at-tached to outer edge of fiber above), filiform,loosely curled and intertangled; fruits postma-ture and weathered, erect, on sharply reflexedpedicels.

Supplemental collection: F. S. Ward s.n., 5June 2010. Dry open mixed-deciduous wood-land, Hill Road, Gloucester Point, VIRGINIA(FLAS). Inflorescence 1.5–2.5 m tall (panicle0.7–1.0 m tall, atop naked scape); inflores-cence axis, branches, and pedicels glabrous;scape with prominent obtuse, distally concave,remote bracts; branches of panicle un-branched, stiffly ascending-erect, 12–18 cmlong; flowers pendent, numerous, crowded;pedicels 0.8–1.2 cm long; buds white, 4.0–4.5cm long; sepals white, elliptic, 4.5–5.0 cmlong, 1.5 cm broad; petals white, broadlyelliptic, 4.8–5.0 cm long, 2.3–2.5 cm broad;stamens 2.0–2.2 cm long (filaments glandu-lar-pubescent, diverging on distal half; an-thers <1 mm long, white to yellow); pistil 3.0–3.5 cm long, much exceeding stamens (styleslightly narrower than ovary, 1.5 cm long,with 3 erect stigmas); capsules (of previousyear) 2.5–3.0 cm long, often constricted atmiddle, erect, dry; seeds dark brown, flat, 6–7mm long.

DIFFERENCES BETWEEN THE TAXAYucca filamentosa, as found in its type

locality of Gloucester, Virginia, and Yuccaflaccida, as represented by its neotype inGilchrist County, Florida, are unquestion-ably closely related taxa. The general formof the plant, with a basal rosette of stiffleaves from which arise a tall, erect panicle;the slender fibers that partially detach fromthe leaf margins; the structure of the flowersand fruits; are all clearly homologous. But if

2012 275WARD: YUCCA FILAMENTOSA AND YUCCA FLACCIDA IN THEIR TYPE LOCALITIES

the two taxa are to be separated, it is the few

differences that must be emphasized.

Most striking is the difference between thetwo taxa in the form of their leaves. Yuccaflaccida, with its narrow, nearly linear leaves(Ward 2006, figures 1, 2), would blend in wellif it were to grow in the western States, among

the numerous other narrow-leaved Filiferae ofthat region. But Yucca filamentosa, with itsmuch broader, deeply concave leaves (Figure1), seems not to be approached by any otherNorth American species. The ability to observethis three-dimensional characteristic is greatly

diminished when the leaves are pressed,although often an apical puckering remains.Almost never is this feature noted in botanicalliterature, though occasional use of the com-mon name, ‘‘Spoon-leaf Yucca’’ (Tatnall 1946;

Fernald 1950, p. 438; Hyam and Pankhurst1995, p. 533), attests to its observation in thefield. This concave cross-sectional shape indi-

cates Fernald (1944), who knew the plantwell, was correct in equating Haworth’s Y.

concava with Y. filamentosa.

The semidetached leaf-margin fibers alsodiffer. Those of typical (i.e., Gadsden Co.,Florida) Yucca flaccida are relatively short,

rarely exceeding 4 cm; they are rather stiff,each shorter than the distance to the base ofthe next fiber above. Those of Yucca filamento-sa are more slender, much longer (to 20 cm),with each overlapping and attached to theback of two or more of the fibers above; thefibers thus remain attached both proximallyand digitally. A view into the center of ahealthy plant shows a conspicuous tangle ofthese fibers. This characteristic, too, is almostunmentioned in botanical literature; onlyDress (1976, p. 1178) contrasts the two taxaon this feature.

The inflorescences of both Yucca flaccida andYucca filamentosa are compact panicles atop

Figure 1. Mature but nonflowering rosettes of Yucca filamentosa, showing concave leaves and tangled leaf-margin

fibers. Gloucester Point, Virginia. June 2009.

Figure 2. Portion of inflorescence of Yucca filamentosa, with closely spaced, pendent flowers. May 2010.

276 VOL. 77CASTANEA

tall, bracted scapes (Figures 3, 4). The panicle

branches of Y. flaccida are straight and

horizontal or are slightly inclined or, with

weight of the maturing capsules, somewhat

declined (Ward 2006, figures 1, 3, and 4).

However, the panicle branches of Y. filamento-

sa are strongly ascending with the apical

portion vertical and near-parallel to the

panicle axis. This feature appears not to have

been noticed, although it is so striking that

flowering/fruiting specimens can be readily

distinguished at a distance.

Differences were also found in the flowers

(Figure 2) and fruits. Of the measurements

taken (as shown in the epitype selection,

above), the most notable were: (a) the petals

of Y. filamentosa are appreciably broader than

the sepals (vs. somewhat broader in Y.

flaccida, (b) the pistil of Y. filamentosa well

exceeds the stamens (vs. slightly shorter in Y.flaccida), (c) the style of Y. filamentosa issomewhat narrower than the ovary (vs.clearly narrower in Y. flaccida), and (d) thestyles of Y. filamentosa are erect (vs. divergingin Y. flaccida). The fruits of both species aredry, erect capsules, similar in size and in beingborne erect on abruptly reflexed pedicels.Capsules of Y. flaccida are cylindric-ellipsoid.But many capsules of Y. filamentosa show acurious midpoint constriction, a ‘‘wasp-waist.’’Fernald (1944) also observed this feature; hedescribed the capsules as ‘‘inclined to beconstricted at or near the middle and dumb-bell-like."

CONCLUSIONS AND RECOMMENDA-TION The judgment as to whether twopopulations represent one species, or two, is asold as the concept of ‘‘species’’ itself. This topic

Figure 3. Yucca filamentosa plant, ca. 3 m height, in early flowering with uppermost flowers still in bud. May 2010.

Figure 4. Postflowering Yucca filamentosa plant, showing compact inflorescence and strongly ascending branches

of the panicle. With Joseph H. Brown, June 2009.

2012 277WARD: YUCCA FILAMENTOSA AND YUCCA FLACCIDA IN THEIR TYPE LOCALITIES

has been well discussed elsewhere (Judd et al.1999, p. 127–132), and need not be reviewedhere. But applied taxonomic judgment invari-ably involves comparison of a new classifica-tion with other, more familiar interspeciesrelationships. What is accepted in othergroups serves as a guide to the new situation.

Here, any conclusion as to the status of thetwo populations of closely related taxa ofYucca must be tempered with caution. Noinformation is available to show the degree ofintergradation of morphology, or of sexualincompatibility. Even chromosome counts ofclearly identified plants seem lacking. It isclear that future examination might tilt thedecision one way or the other. But the strikingdifferences manifested by the two type popu-lations inclines the judgment, as based onpresent knowledge, that Yucca filamentosa andYucca flaccida should be retained at the level ofspecies.

ACKNOWLEDGMENTS I am most grateful

to members of the John Clayton chapter of theVirginia Native Plant Society, and especially toJoseph H. Brown, for guidance to the popula-tion of Yucca filamentosa near Gloucester,Virginia, and shipment to Florida (via FedEx) of plants in different stages of develop-ment. I appreciate the manuscript reviewgiven me by Alan S. Weakley. I thank ForrestS. Ward for the photographs and for hispatience and companionship on our searchfor John Clayton’s Yucca.

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