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The families of flowering plants

L. Watson and M.J. Dallwitz

Dioscoreaceae R. Br.

Including Cladophyllaceae Dulac, Stenomeridaceae J.G. Agardh, Tamaceae S.F. Gray; excluding Trichopodaceae.

Habit and leaf form. Shrubs, or herbs, or lianas. ‘Normal’ plants. Rhizomatous, or tuberous (the tubers giving rise to annual stems). Climbing (usully), or self supporting (rarely); mostly stem twiners, or scrambling (or trailing); Tamus twining clockwise. Mesophytic, or xerophytic. Leaves alternate (usually), or opposite (rarely); usually spiral; petiolate; sheathing to non-sheathing; simple (usually), or compound; when compound, palmate (with three to six or more leaflets). Lamina entire (usually), or dissected (occasionally); when incised, palmatifid; basically palmately veined; cross-venulate; often cordate, or sagittate. Leaves stipulate, or exstipulate.

Leaf anatomy. Extra-floral nectaries present (often), or absent. Stomata present; anomocytic. The mesophyll usually containing crystals. The crystals raphides (in mucilaginous idioblasts). Minor leaf veins without phloem transfer cells (Dioscorea).

Axial (stem, wood) anatomy. Secondary thickening absent, or anomalous (e.g. Dioscorea, the vascular bundles arranged in two concentric circles). The anomalous secondary thickening when present, from a single cambial ring.

The vessel end-walls scalariform.

Root anatomy. Roots with velamen (single layered), or without velamen. Root xylem with vessels; vessel end-walls scalariform.

Reproductive type, pollination. Plants dioecious (usually), or monoecious, or hermaphrodite (Stenomeris). Floral nectaries present. Nectar secretion from the gynoecium (via septal nectaries). Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in panicles, in racemes, and in spikes. The ultimate inflorescence units racemose. Inflorescences axillary. Flowers bracteate; bracteolate (one bracteole, rarely two); small (generally inconspicuous); regular; 3 merous. Perigone tube usually present (short).

Perianth of ‘tepals’; 6; joined; 2 whorled; isomerous; sepaloid, or petaloid; similar in the two whorls, or different in the two whorls.

Androecium 6 (usually), or 3 (the inner whorl sometimes missing). Androecial members adnate (to the perianth); free of one another, or coherent; when cohering 1 adelphous (the filaments connate into a tube); 2 whorled (usually), or 1 whorled (by reduction). Androecium exclusively of fertile stamens, or including staminodes (the inner whorl sometimes staminodal or obsolete). Staminodes when present, 3; internal to the fertile stamens. Stamens 6, or 3; isomerous with the perianth, or diplostemonous. Anthers dorsifixed, or adnate; dehiscing via longitudinal slits; extrorse, or introrse; appendaged, or unappendaged. Endothecium developing fibrous thickenings. The endothecial thickenings spiral. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall of the ‘monocot’ type. Tapetum glandular. Pollen grains aperturate; 1 aperturate, or 2–5 aperturate; sulcate, or foraminate, or sulculate; 2-celled.

Gynoecium 3 carpelled. The pistil 3 celled. Gynoecium syncarpous; synovarious to synstylovarious; inferior. Ovary 3 locular. The ‘odd’ carpel posterior. Gynoecium stylate. Styles 1, or 3; free, or partially joined; apical. Stylar canal present. Stigmas dorsal to the carpels; dry type; non-papillate; Group IV type. Placentation axile. Ovules 2 per locule (usually), or 3–50 per locule (i.e., rarely ‘many’); pendulous; superposed; non-arillate; anatropous; bitegmic; crassinucellate. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating. Synergids hooked. Hypostase present. Endosperm formation nuclear.

Fruit fleshy, or non-fleshy; dehiscent, or indehiscent; a capsule (usually), or a berry (Tamus), or a samara (Rajania). Capsules loculicidal. Seeds endospermic. Endosperm oily. Seeds winged (e.g. Dioscorea), or wingless. Seeds without starch. Embryo well differentiated (small). Cotyledons 1 (usually, more or less lateral, broad and flat), or 2 (the second rudimentary). Embryo achlorophyllous (1/1). Testa without phytomelan; with red to yellowish brown phlobaphene.

Seedling. Hypocotyl internode present, or absent (sometimes developing into a storage organ). Seedling collar not conspicuous. Cotyledon hyperphyll elongated (Dioscorea), or compact; non-assimilatory; of Dioscorea dorsiventrally flattened (but anatomically unifacial). Coleoptile absent. Seedling cataphylls absent. First leaf dorsiventral. Primary root ephemeral.

Physiology, phytochemistry. Accumulated starch other than exclusively ‘pteridophyte type’. Not cyanogenic. Alkaloids present, or absent (mostly). Saponins/sapogenins commonly present. Proanthocyanidins present (commonly in Dioscorea, often abundant), or absent (e.g. Tamus); when present, cyanidin. Flavonols present (commonly and abundantly, in Dioscorea), or absent (Tamus); kaempferol and quercetin. Ellagic acid absent. Sieve-tube plastids P-type; type II.

Geography, cytology. Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Temperate (warm), sub-tropical to tropical. Widespread, but mainly tropical. X = 9, 10, 12, 14.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Liliiflorae; Dioscoreales. APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order Dioscoreales.

Species 750. Genera 6; Borderea, Dioscorea, Epipetrum, Rajania, Stenomeris, Tamus.

Economic uses, etc. Several important food plants, notably yams (Dioscorea).


Now climbing high with random maze,
O’er elm, and ash, and alder strays;
And round each trunk a network weaves
(Of Tamus communis, quoted by Ann Pratt, ‘Wild Flowers’ (1857), unattributed)

Illustrations. • Technical details: Dioscorea. • Technical details: Dioscorea (Thonner). • Technical details: Tamus, Testudinaria. • Dioscorea elephantipes: Bot. Reg. 921, 1825. • Dioscorea humilis, as D. pusilla: Hook. Ic. Pl. 7–8 (1844). • Dioscorea buchananii: Hook. Ic. Pl. 14 (1880–82). • Rajania hastata: Hook. Ic. Pl. 14 (1880–82). • Tamus communis (B. Ent., 1833). • Tamus communis (J. E. Sowerby, 1861).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 20th June 2017.’.