Dioscoreaceae R. Br.
Including Cladophyllaceae Dulac, Stenomeridaceae J.G. Agardh, Tamaceae S.F. GrayExcluding Trichopodaceae
Habit and leaf form. Shrubs, or herbs, or lianas. Plants autotrophic. 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.
General anatomy. Accumulated starch other than exclusively ‘pteridophyte type’.
Leaf anatomy. Extra-floral nectaries present (often), or absent. Stomata present; anomocytic.
The mesophyll usually containing calcium oxalate crystals. The mesophyll crystals raphides (in mucilaginous idioblasts). Minor leaf veins without phloem transfer cells (Dioscorea).
Stem anatomy. Secondary thickening absent, or anomalous (e.g. Dioscorea, the vascular bundles arranged in two concentric circles); when present, from a single cambial ring. Xylem with vessels. Vessel end-walls scalariform. Sieve-tube plastids P-type; type II.
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 unit 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 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, biochemistry. Not cyanogenic. Alkaloids present, or absent (mostly). 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. Saponins/sapogenins commonly present.
Geography, cytology. Holarctic, Paleotropical, Neotropical, Cape, Australian, and Antarctic. Temperate (warm), or 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).
• Technical details: Dioscorea.
• Technical details: Dioscorea (Thonner).
• Technical details: Tamus, Testudinaria.
• Dioscorea elephantipes: Bot. Reg. 921, 1825.
• Tamus communis (B. Ent.).
• Tamus communis (J. E. Sowerby, 1861).
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)