bonnetiaceae

8/14/2019 Bonnetiaceae

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BonnetiaceaeBonnetiaceae (Bartl.) L. Beauvis. ex Nakai in Bull. Tokyo Sci. Mus. 22:25 (1948).

A.L. Weitzman, K. Kubitzki, and P.F. Stevens

More or less subpachycaulous small to medium-sized trees and shrubs. Leaves convolute, spiral,crowded towards apex of branches, with close, as-cending lateral veins, margins serrulate, initially setulose, estipulate; petiole short or 0. Flowers sin-gle, or more or less cymose inflorescences; pedicels

with 2 prophylls or several bracts; flowers bisex-ual, cyclic; sepals 5, unequal, free, quincuncial;petals 5, contorted, free; stamens numerous; fila-ments slender, free, or basally connate into 5 an-tepetalous bundles; anthers short, basifixed; fasci-clode + or 0; ovary 3(–5)-locular, with numerousorderly arranged ovules on biseriate axile placen-tae; stylodia free or united into a branched or sim-ple style; stigmas papillate. Fruits septicidal cap-sules with a persistent central column; seeds withscanty endosperm; embryo straight.

Three genera and about 40 species, northern

South America, West Indies, Southeast Asia, WestMalesia, Moluccas and New Guinea.

Vegetative Morphology and Anatomy. Bon-netiaceae are stout-stemmed shrubs or usually small trees with few branches. The smallest spe-cies, Bonnetia ahogadoi, is notable for its trailingand rooting inflorescence axis which also acts asa stolon (Fig. 10), whereas Ploiarium alterniflorum,a small, stilt-rooted tree, may grow up to 25m highon swampy peat soil in Johore (Corner 1978). The

terminal bud usually lacks scales, axillary budsare small, and branching appears to be sylleptic,althoughin B. ahogadoi growth ofthe main axis ap-pears to be rhythmic (Steyermark 1984) and thereare scales at the base of flagelliform inflorescenceshoots. The leaves remain rolled up as the budelongates, and are more or less sessile and usually have a distinct but not very prominent midrib.The plants are completely glabrous, except for tiny colleters found in the leaf axils. The leaf margin isusually minutely serrulate and only rarely entirebut, in the juvenile stage, it is always provided with

minute setae which fall off during leaf expansion

but persist in the tiny, revolute leaves of Bonnetiaroraimae. Archytaea and Ploiarium have vascu-larised, disciform structures borne immediately inside the margin and on the lower surface of the blade and in its upper one-third. Venation isoften eucamptodromous, sometimes more or less

brochidodromous or parallelodromous.The phellogen in the stem is surficial in origin,that in the root is initiated 3 or 4 layers deep inthe cortex. There are brachysclereids in the stemcortex, a sheath of fibres in the pericyclic posi-tion, and groups of fibres in the secondary phloem(see also van Tieghem 1885). The heartwood isdark reddish brown and heavy. Vessel elements aresolitary, of medium length, and their perforationsare simple/transverse; uniseriate rays are of up-right cells, and multiseriates (2–4 cells wide) con-sist of procumbent cells with uniseriate extensions

of upright cells; axial parenchyma is scanty para-tracheal, and fibres are mostly thick-walled. Xylemparenchyma forms an adaxial cap on the vessels.

Nodesare trilacunarin Bonnetia,unilacunarin Archytaea and Ploiarium. The separate traces arevisible in leaf scars although, in taxa such as Bon-netia ahogadai, traces are more or less confluentin the outer part of the cortex. Ploiarium has anarcuate midrib bundle, that of other taxa is morecomplex, the tissue on the adaxial side in partic-ular being irregularly arranged. Vascular bundles

are embedded, and the marginal setae of Archy-taea and Ploiarium, but not those of Bonnetia, areassociated with vascular tissue.

Stomata are anomocytic and an adaxial hypo-dermis is sometimes present. The leaf anatomy of Bonnetia is remarkable: the epidermis is often mu-cilaginous and its cells bulge and intrude betweenthe mesophyll cells; foliar sclereids are widespreadin the mesophyll; and the leaf midrib and all veinsincluding the terminal veinlets are surrounded by an endodermis of thin-walled cells provided withCasparian strips (Maguire 1972; Dickison and

Weitzman 1996; Weitzman and Stevens 1997).



Bonnetiaceae 37

Inflorescence and Flowers. Inflorescencesare lateral, and several species appear to haveaxillary flowers. However, these are probably reduced inflorescences, and the “pedicels” bear2–several bracts along their length, sometimesvery close to the calyx. The sepals of Bonnetia,

and perhaps also Ploiarium, are terminated by setae very like those found on the leaf margins.The petals are predominantly white or pink.Whether or not the androecium of Bonnetiais fasciculate needs study; fascicles have beenreported (e.g. Steyermark 1984) but their existence– at least, as evident in later bud or flower – hasbeen questioned (Kobuski 1948; PFS, pers. obs.).It is not known if the fasciclodes of Ploiariumsecrete nectar; otherwise, there are no reports of nectar from the family (Dickison and Weitzman

1998).

Pollen Morphology. Pollen is 28 to almost60 µm long, oblate-spheroidal, tricolporate withwide colpi and circular ora. Sometimes, as inB. lancifolia, the colpi are fused at the poles,leaving a triangular polar space. There are costalcolpi in Archytaea and Ploiarium, and all taxahave costal pori. The nexine, 0.5–4 µm thick, isthicker than the sexine, which is finely reticulate(Erdtman 1952; Maguire 1972; Steyermark 1984;Salgado-Laboriau and Villar de Seoane 1992).

Seed. The seeds are quite small, and Corner(1976) suggested that the seed coat of Ploiarium isprobably endotestal, although its development hasnot been studied. Exotestal cells are thin-walledand polygonal, endotestal cells are usually iso-diametric, low, and with sinuous anticlinal walls,lignification is extensive and there are numerousnarrow plasmodesmata. Ploiarium alternifoliumhas rather elongated endotestal cells, and the anti-clinal walls of those of Archytaea are almost

straight. There is a thin, persistent layer of endo-perm surrounding the straight embryo. Althoughthe cotyledons are generally small, those of Bonnetia range from 1/2–1/6 the length of theembryo. Germination is epigeal (Ploiarium).

Phytochemistry. Bonnetiaceae are rich in xan-thones with various substitution patterns, and bi-xanthones and anthraquinone xanthones havebeen reported from Ploiarium (Kubitzki et al.1978; Bennett et al. 1990). Xanthones are alsorichly diversified in Clusiaceae and Hypericaceae

(Bennett and Lee 1989).

Family Circumscription and Affinities.

When the exudate-producing genus Neotatea andthe anther gland-bearing genera around Kielmey-era and Caraipa are removed from Bonnetiaceae,as suggested by Weitzman and Stevens (1997), thefamily becomes very homogeneous. Although in

the past members of the family have been includedin the “intermediate” zone between Theaceaeand Clusiaceae/Hypericaceae, the former arenow in Ericales, and possession of xanthones,floral morphology, testa anatomy, etc., all linkBonnetiaceae with Clusiaceae/Hypericaceae. Thecombination of characters of wood anatomicalcharacters presented above sets Bonnetiaceaeapart from Theaceae, with which Baretta-Kuipers(1976) compared them, and also Guttiferae andHypericaceae.

Gene sequence analyses by Savolainen,Fay et al. (2000) and Gustafsson et al. (2002)confirm the close relationship of Bonnetiaceaewith Clusiaceae/Hypericaceae. The inclusion of Ploiarium in Malvales (Savolainen, Fay et al.2000) was probably due to a mistaken identifica-tion, since i.a. the distinctive seed coat anatomy of Archytaea is quite unlike that of Malvales.Elatinaceae have also often been consideredas possibly related to Bonnetiaceae, agreeingin testa anatomy and a number of other fea-tures, but molecular data place them sister to

Malpighiaceae (Davis and Chase 2004); whetheror not that family is close to Bonnetiaceae, etc., isunclear.

Distribution and Habitats. The two closely related, small genera Archytaea and Ploiariumare disjunct between Southeast Asia/Malesia andnorthern South America, whereas Bonnetia isrestricted to continental South America, with onespecies on Cuba.

Archytaea prefers open habitats, often by

creeks, always on nutrient-poor soil, rangingfrom lowland to mid-altitudes. Bonnetia is mostspeciose in the Guayana Highland and its sur-roundings, where 27 species are found, all butone (B. paniculata) of which are endemic to thisregion. Most of them have only a limited altitudinalrange, with the majority preferring the mesother-mic/submicrothermic belt (1,200–2,700m; Huber1988), but Bonnetia crassa spans a belt of 2,000m.With increasing altitude, the bonnetias tend tobe of lower stature. Bonnetia ahogadoi is a low shrublet growing at localized sites on peat in rock

depressions of the Chimatá Massif in Venezuela



38 A.L. Weitzman, K. Kubitzki, and P.F. Stevens

Fig. 10. Bonnetiaceae. Bonnetia ahogadoi. A Habit. B Leaf.C Flower. D Androecium andgy noecium.E Anther. F Ovary,transversal section. G Capsule at beginning of dehiscence.

H Two valves of dehiscent capsule with adherent seeds andpersistent columella. I Seeds, various positions. (Drawingby B. Manara; Steyermark 1984)

at an altitude of about 2,100m (Huber 1992).Ploiarium grows in the lowland, often close to thesea, and on swampy peaty soil (Corner 1978) or onnutrient-poor white sand in the heath forests of Borneo.

Uses. The wood is durable and in Asia/Malesialocally used for constructions, but is not a com-mercial timber.

Key to the Genera

1. Androecium not fasciculate; ovary 3(4)-locular3. Bonnetia

– Androecium 5-fasciculate; ovary 5-locular 22. Flowers in 3–many-flowered inflorescences; sepals and

stamens caducous; style simple 2. Archytaea– Flowers solitary; sepals and stamens persistent; stylo-

dia 5, free to base 1. Ploiarium

Genera of Bonnetiaceae

1. Ploiarium KorthalsPloiarium Korthals, Verh. Nat. Gesch. Bot., ed. Temminck:

135 (1840); Kobuski, J. Arnold Arb. 31:196–207 (1950), rev.

Trees, sometimes vast, or shrubs. Flowers solitary;

pedicels ancipitous, increasing in diametertowardsapex; sepals caducous; nectary glands 5, alternat-ing with petals; stamens numerous, caducous, in5 antesepalous fascicles; ovary 5-locular; stylodia5, free to base, persistent. Capsule dehiscing fromthe base; seedslinear; endospermfleshy. Three spe-cies, from Cambodia through Malay Peninsula toSumatra, Borneo and Halmahera.

2. Archytaea Mart. Archytaea Mart. in Mart. & Zucc., Nov. Gen. Sp. Pl. 1:116

(1826); Weitzman & Stevens, BioLlania Esp. 6:556–557

(1997); Weitzman, Fl. Venez. Guayana 9:310–313 (2005).



Bonnetiaceae 39

Small trees or shrubs. Inflorescences axillary, 3–many-flowered; peduncles ancipitous, increasingin diameter towards apex; pedicels midway withprophylls; sepals persistent; nectary glands 5,alternate with petals; stamens numerous, persis-tent, in 5 antesepalous fascicles; ovary 5-locular;

style simple, persistent. Seeds numerous, linear,imbricate, exalbuminous. Two species, in theGuayana sandstone region and adjacent lowlandsof northern South America.

3. Bonnetia Mart. Fig. 10

Bonnetia Mart. in Mart. & Zucc., Nov. Gen. Sp. Pl. 1:114

(1826), nom. cons.; Kobuski, J. Arnold Arb. 29:393–413

(1948), rev.; Weitzman, Fl. Venez. Guayana 9:313–324

(2005).

Neblinaria Maguire (1972).

Neogleasonia Maguire (1972) except N. duidae (Kobuski & Steyerm.) Maguire

Acopanea Steyerm. (1984).

Trees or shrubs. Flowers solitary or up to threeon axillary peduncles or occasionally arranged inloose panicles with ancipitous or terete pedun-cles; sepals persistent; stamens very numerous,persistent, the filaments adnate to the base of the ovary and otherwise free; anthers dehiscinglongitudinally or by two pores at the base; ovary 3(4)-celled; stylodia 3, or style simple and then

sometimes apically branched. Seeds linear, elon-gated above and below into a small membranouswing. About 29 species, mainly in the Guayanahighland and adjacent regions, with B. paniculataSpr. ex Benth. extending along the Andes to Peru,B. stricta (Nees) Nees & Mart. along the Atlanticcoast southwards to Rio de Janeiro, and B. cubensis(Britton) Howard in Cuba.

Selected Bibliography

Baretta-Kuipers, T. 1976. Comparative wood anatomy of Bonnetiaceae, Theaceae and Guttiferae. In: Baas, P.,Bolton, A.M., Catling, D.M. (eds) Wood structure inbiological and technological research. Leiden Botani-cal Series 3, pp. 76–101.

Bennett, G.J., Lee, H.-H. 1989. Xanthones from Guttiferae.Phytochemistry 28:967–998.

Bennett, G.J., Lee, H.-H., Lowrey, T.K. 1990. Novel metabo-lites from Ploiarium alternifolium: a bixanthoneand two anthraquinolyxanthones. Tetrahedron Lett.31:751–754.

Corner, E.J.H. 1976. See general references.

Corner, E.J.H. 1978. The freshwater swamp-forest of SouthJohore and Singapore. Gard. Bull. suppl. 1. Singapore:Government Printers.

Davis, C.C., Chase, M.W. 2004. Elatinaceae are sister toMalpighiaceae,andPeridiscaceae aremembersof Saxi-fragales. Amer. J. Bot. 91:262–273.

Dickison,W.C., Weitzman, A.L. 1996.Comparativeanatomy of the young stem, node and leaf of Bonnetiaceae, in-cluding observations on a foliar endodermis. Amer. J.Bot. 83:405–418.

Dickison, W.C., Weitzman, A.L. 1998. Floral morphology and anatomy of Bonnetiaceae. J. Torrey Bot. Soc.125:268–286.

Erdtman, G. 1952. See general references.

Gustafsson, M.H.G., Bittrich, V., Stevens, P.F. 2002. Phy-logeny of Clusiaceae based on rbcL sequences. Intl J.Pl. Sci. 163:1045–1054.

Huber, O. 1988. Guayana highlands versus Guayana low-lands, a reappraisal. Taxon 37:595–614.

Huber, O. 1992. La vegetación. In: Huber, O. (ed.) El macizode Chimatá. Caracas: Todtmann, pp. 161–177.

Kobuski, C.E. 1948. Studies in the Theaceae, XVII. A review of the genus Bonnetia. J. Arnold Arb. 29:393–413.

Kubitzki, K., Mesquita, A.A.L., Gottlieb, O.R. 1978.Chemosystematic implications of xanthones inBonnetia and Archytaea. Biochem. Syst. Ecol.6:185–187.

Maguire, B. 1972. Bonnetiaceae. In: The Botany of the

Guyana Highland. Part IX. Mem. New York Bot. Gard.23:131–165.Prakash, N., Lau, Y.Y. 1976. Morphology of Ploiarium al-

ternifolium and the taxonomic position of Ploiarium.Bot. Notiser 129:279–285.

Salgado-Laboriau,M.L.,Villarde Seoane, L. 1992.Contribu-ción a la flora polínica de los tepuyes. In: Huber, O.(ed.) El macizo de Chimatá. Caracas: Todtmann, pp.219–236.

Savolainen, V., Fay, M.F. et al. 2000. See general references.Steyermark, J.A., 1984. Theaceae (Bonnetiaceae), pp. 323–

330. In: Flora of the Venezuelan Guayana, I. Ann. Mis-souri Bot. Gard. 71:297–340.

van Tieghem, Ph. 1885. Second mémoire sur les canaux

sécréteurs des plantes. Ann. Sci. Nat. VII, Bot. 1:5–96;see particularly Ternstroemiacées, pp. 43–46.Weitzman, A.L., Stevens, P.F. 1997. Notes on the circum-

scription of Bonnetiaceae and Clusiaceae, with taxaand new combinations. BioLlania Edic. Esp. 6:661–564.

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