Dioscoreaceae R.Br.

Dioscoreaceae, J. Miège. Flora of West Tropical Africa 3:1. 1968

Bracts

Bracteole generally present in oblique position

Flowers

Flowers placed singly along the axis or in short few-flowered lateral cymules Flowers small, inconspicuous, actinomorphic Male flowers sessile or shortly pedicelled

Androecium

Filaments free or shortly connate; anthers 2-locular Stamens 6, or 3 with or without 3 staminodes

Female

Female inflorescences: spikes looser, longer than the male ones, solitary or paired or sometimes more numerous, in the leaf axils

Sterile Parts

Staminodes 0, 3 or 6 Rudimentary ovary frequent

Gynoecium

Ovary inferior, 3-locular Style 3, free or connate Placentation axile: 2 anatropous ovules in each loculus

Tubers

Tubers toxic or edible, often protected by thorny roots

Bulbils

Aerial tubers (bulbils) present or absent

Stem

Stems glabrous or pilose

Leaves

Leaves moving, following the conditions of lighting Basal leaves often reduced Petiole generally twisted and sometimes jointed at the base or with more or less leathery auricles Leaves alternate or opposite (sometimes both on the same plant), often cordate, entire or lobulate, more or less digitately nerved or palmately compound, acumen often large and glandulose

Habit

Plants dioecious; exceptionally on the same inflorescence are clustered male and female flowers6 Climbers (at least the West African species), spiny or not, annual or perennial with tubers annually renewed or perennial

Inflorescences

Inflorescence spicate, racemose or paniculate Female inflorescences: spikes looser, longer than the male ones, solitary or paired or sometimes more numerous, in the leaf axils Male inflorescences: spikes generally several in the leaf axils, sometimes clustered in racemes or compound panicles

Perianth

Perianth campanulate or spreading, 6-lobed, lobes 2-seriate, often connate at the base

Male

Male flowers sessile or shortly pedicelled Male inflorescences: spikes generally several in the leaf axils, sometimes clustered in racemes or compound panicles

Fruits

Fruits (in the tropical African species) 3-valved capsules

Seeds

Seeds winged, with albumen

Wilkin, P. (2009). Neotropical Dioscoreaceae.

Morphology

Description

Rhizomatous perennials, rhizome often short and usually subtending one to several annually to perennially replaced tubers. Stems herbaceous or woody at base, twining (tendrils lacking), rarely erect or absent in acaulescent perennial herbs with a basal rosette of leaves. Leaves opposite to alternate , entire to compound , base often cordate , venation campylodromous (or leaves compound ), secondary venation reticulate ; petiole usually with a basal and apical pulvinus except in acaulescent species. Inflorescences usually axillary , sometimes borne on a leafless, herbaceous scape, flowers solitary or in panicles, cymes, spikes, or racemes. Flowers trimerous, epigynous , almost all actinomorphic , rarely hermaphrodite , usually unisexual and plants dioecious . Tepals 6. Stamens usually 6. Ovary inferior, 3-locular, rarely 1-locular. Fruit usually capsular, rarely leathery and indehiscent or samaroid; dehiscence loculicidal, irregular or indehiscent . Seeds smooth, flattened and winged , or wingless and either globose and smooth, or with 16-18 longitudinal ridges.

Distribution

Distribution in the Neotropics

• Dioscorea L. - throughout the Neotropics.
• Tacca parkeri Seem. - Northern South America only.

Diagnostic

Distinguishing characters (always present)

• Campylodromous leaf venation (or homologous compound leaves).
• No tendrils.
• Inferior ovary.

Other important characters

• Perennial or annual.
• Usually underground tuber.
• Twining stem (a few erect dwarf Dioscoreas and Tacca parkeri are rosette -forming herbs).
• Basal and apical petiolar pulvini.
• Reticulate secondary leaf  venation.
• Dioecious.
• 3-wingedcapsule with 3 locules (Dioscorea) or 6-ribbed leathery indehiscentfruit with 1 locule (T. parkeri).

Key differences from similar families

From Smilacaceae:

• No tendrils (tendrils from petiole in Smilacaceae).
• Basal and apical pulvini (none in Smilicaceae). 
• Inflorescence a spike/raceme or derived form (not an umbel).
• Dioecious
• Ovary inferior (not superior).
• Fruit a capsule or leathery/indehiscent (not a berry).

From Menispermaceae:

• Campylodromous (not pinnate) venation.
• Parts in 3s/6s, (Menispermaceae not so).

Closest relative Burmanniaceae is morphologically very reduced and usually heteromycotrophic.

Useful tips for generic identification

See below

Notable genera and distinguishing features

Dioscorea:

• Possesses a stem.
• Inflorescence with flowers solitary or in panicles, cymes, spikes, or racemes but not a pseudo-umbel.
• Bracts usually small and never dimorphic as in Tacca.
• Flowers usually unisexual.
• Ovary 3-locular.

Tacca:

• Lacks a stem.
• Inflorescence a cymose pseodo-umbel.
• Large foliaceous and pendent filiform bracts.
• Flowers perfect.
• Ovary 1-locular.

General Description

Number of genera

• 2, Dioscorea and Tacca Forst. & Forst. f. (1 rather rare species in Northern South America, T. parkeri).

Status

• Both genera native.
• Cultivated native (rarely) and non-native Dioscorea also encountered.

Notes on delimitation

• Dioscoreales. See Angiosperm Phylogeny Website. Older treatments/textbooks suggest Dioscoreaceae are "primitive" monocots among the closest to Dicots. This is not so.
• Most treatments pre-2000 separate Taccaceae, but these are now considered together.

Literature

Important literature

Barroso, G.M., D. Sucre, E.F. Guimares, L.F de Carvalho, M. Conceicao Valente, J. Dames e Silva, J.B. da Silva, F.R. Timno Rosenthal Cinesio Maximo Barbosa, A.N. Roseira and O.M.B Alda F. Barbosa. 1974. Flora de Guanabara Dioscoreaceae. Sellowia 25: 9-256.

Drenth, E. 1972. A revision of the family Taccaceae. Blumea 20: 367-406.

Kirizawa, M. Flora Fanerogamica da Reserva do Parque Estadual das Fontes do Ipiranga (Sao Paulo, Brasil). 196 - Dioscoreaceae. Hoehnea 9:131-133.

Knuth, R. 1924. Dioscoreaceae. In: Engler H. G. A., ed. Das Pflanzenreich, 87 (IV. 43), Leipzig, 1-387.

Pedralli, G.G. 2002. Levantamento floristico das Dioscoreaceae (R. Br.) Lindley da cadeia do Espinhaco, Minas Gerais e Bahia, Brasil. Bol. Bot. Univ. Sao Paolo 20: 63-119.

Prieto C, A., J.L. Fernandez-Alonso and R.L. Liesner. 2000. Nota sobre la familia Taccaceae  (Liliidae) y su presencia en Colombia. Caldasia 22: 265-270.

Sosa, V., B., G. Schubert, and A. Gomez-Pompa. 1987. Flora de Veracruz: Dioscoreaceae. Xalapa: Instituto Nacional de Investigaciones Sobre Recursos Bioticos.

Tellez V., O. and B. G. Schubert. 1994. Dioscoreaceae. Pp.54-65 in Flora Mesoamericana Volumen 6, Alismataceae a Cyperaceae, eds. G. Davidse, M. Sousa S. and A. O. Chater. Mexico D.F.: Universidad Nacional Autonoma de Mexico.

[Knuth's treatment is still the only regional monograph. The quality of the others is variable; The Flora Mesoamericana treatment is much better than those from Brazil].

Taccaceae, Susan Carter. Flora of Tropical East Africa. 1962

Habit

Tuberous, perennial herbs

Leaves

Leaves erect, large, basal, petiolate, the base of the petiole channelled or sheathing ; leaf-blade entire, palmate, digitate or pinnatisect

Reproductive morphology

Flowering stems 1–3, basal, erect, simple, leafless

Inflorescences

Inflorescence terminal, umbellate with numerous, pedicellate flowers usually surrounded by a whorl of filiform bracts, and 4–12 large, foliaceous bracts on the outside

Flowers

Flowers bisexual

Perianth

Perianth-segments 6, petaloid, connate at the base, persistent

Androecium

Stamens 6, adnate to the perianth-segments ; filaments hooded and lobed ; anthers 2-celled, dehiscing longitudinally, introrse, situated on the inside of the hood, and projecting outwards between the lobes

Gynoecium

Ovary inferior, unilocular with 3 parietal placentas ; ovules many ; style short; stigma 3-lobed and umbrella-shaped with the stigmatic surface beneath

Fruits

Fruit capsular or baccate

Seeds

Seeds many, with copious endosperm

Taccaceae, F.N. Hepper. Flora of West Tropical Africa 3:1. 1968

Habit

Perennial herbs with a tuberous or creeping rhizome

Leaves

Leaves all radical, large, entire or much lobed

Flowers

Flowers actinomorphic, hermaphrodite, umbellate; bracts forming an involucre, the inner often thread-like

Perianth

Perianth with a short tube and 6 lobes, lobes 2-seriate, mostly somewhat corolline

Androecium

Stamens 6, inserted on the perianth; filaments short; anthers 2-celled, opening lengthwise

Gynoecium

Ovary inferior, 1-celled, with 3 parietal placentas; style short, the 3 stigmas often petaloid and reflexed over the style; ovules numerous

Fruits

Fruit a berry or rarely opening by valves

Seeds

Seeds numerous, with copious endosperm and minute embryo