1. Dioscoreaceae R.Br.

    1. This family is accepted.

[FTEA]

Dioscoreaceae, E. Milne-Redhead. Flora of Tropical East Africa. 1975

Habit
Twining herbs with annual stems arising from tubers or rhizomes, rarely stems self-supporting
Leaves
Leaves alternate or opposite, often ovate-cordate, but sometimes with 3–7 digitate leaflets
Flowers
Flowers bisexual or unisexual, the latter usually dioecious
Perianth
Perianth segments biseriate, usually united basally
Androecium
Stamens (3, 4) 6
Gynoecium
Ovary inferior, rarely semi-inferior or superior, (1)3-locular
Fruits
Fruit a dehiscent capsule, samara or berry
[FWTA]

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
[NTK]

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].

[FTEA]

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
[FWTA]

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

Images

Dioscoreaceae R.Br. appears in other Kew resources:

First published in Prodr. [A. P. de Candolle] 294. 1810 [27 Mar 1810] (1810)

Accepted by

  • APG IV (2016) http://dx.doi.org/10.1111/boj.12385

Sources

Flora of Tropical East Africa
Flora of Tropical East Africa
http://creativecommons.org/licenses/by-nc-sa/3.0

Flora of West Tropical Africa
Flora of West Tropical Africa
http://creativecommons.org/licenses/by-nc-sa/3.0

Kew Names and Taxonomic Backbone
The International Plant Names Index and World Checklist of Selected Plant Families 2018. Published on the Internet at http://www.ipni.org and http://apps.kew.org/wcsp/
© Copyright 2017 International Plant Names Index and World Checklist of Selected Plant Families. http://creativecommons.org/licenses/by/3.0

Neotropikey
Milliken, W., Klitgard, B. and Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics.
http://creativecommons.org/licenses/by/3.0