Dioscoreales (Yams and Allies)

Abstract

Dioscoreales, the ‘true’ yams and allies, are a group whose current circumscription is dictated by results of molecular phylogenetic analyses. Consisting as it does of several nontraditional members, the group is made up of a heterogeneous set of taxa: unremarkable liliaceous plants, minute chlorophyll‐less plants that live off their associated fungal partners, and large, robust, green plants of the tropics, some of which store starch in large underground tubers (Dioscorea yams) that are important human food across the world, especially in Africa and the Pacific Islands. Some species are important sources of folk medicines and pharmaceuticals; the original birth pills were manufactured from relatives of the edible yams. Dioscorea is remarkable in the ‘dicot’‐like appearance of its stalked, net‐veined leaves borne on vines. Dioscoreales occur across the world and may existed by about 120 million years ago.

Key Concepts:

  • Dioscoreales are herbaceous monocots of northern temperate regions and the tropics.

  • Dioscoreales contain five families: Burmanniaceae, Dioscoreaceae, Nartheciaceae, Taccaceae and Thismiaceae, with 24 genera and 643 species; new species of Burmanniaceae and Thismiaceae are still being discovered.

  • The flower has an inferior ovary, short style and branched stigma, anthers often with apical extension. Many species contain steroidal saponins.

  • The order includes heterotrophs that depend on associated fungi for their nutrition (Burmannicaeae and Thismiaceae) and autotrophic tuberous plants that are a food source for other organisms including humans (Dioscoreaceae).

  • Dioscorea, the genus of ‘true’ yams, contains about 10 cultivated species.

  • Dioscoreales are at least 123 million years old according to molecular clock estimates.

Keywords: true yams; tuber crop; famine food; steroidal saponins; myco‐heterotroph; oral contraceptive; human migration

Figure 1.

Phylogenetic relationships of Dioscoreales (after Merckx et al., ).

Figure 2.

Edible tubers (‘true’ yams): Dioscorea alata tubers just harvested by a cultivator (Gujarat, India).

Figure 3.

Dioscorea (yam), a climber with ‘dicot’‐like leaves: petiole, broad blades and net‐like veneration.

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References

Angiosperm Phylogeny Group [APG III] (2009) An update of the angiosperm phylogeny group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society 161: 105–121.

Burkill IH (1960) The organography and the evolution of Dioscoreaceae, the family of the yams. Journal of the Linnean Society (Botany) 56: 319–412.

Caddick LR, Rudall PJ, Wilkin P, Hedderson TAJ and Chase MW (2002a) Phylogenetics of Dioscoreales based on combined analyses of morphological and molecular data. Botanical Journal of the Linnean Society 138: 123–144.

Caddick LR, Wilkin P, Rudall PJ, Hedderson TAJ and Chase MW (2002b) Yams reclassified: a recircumscription of Dioscoreaceae and Dioscoreales. Taxon 51: 103–114.

Coursey DG (1967) Yams. An Account of the Nature, Origins, Cultivation and Utilisation of the Useful Members of the Dioscoreaceae. London: Longmans.

Drenth E (1976) Taccaceae. In: Steenis CGG Jvan (ed.) Flora Malesiana Series 1: Spermatophyta, vol. 7, part 4, pp. 806–819. Haarlem: P. Noordhoff.

Janssen T and Bremer K (2004) The age of major monocot groups inferred from 800+ rbcL sequences. Botanical Journal of the Linnean Society 146: 385–398.

Merckx V, Schols V, Maas‐van de Kamer H et al. (2006) Phylogeny and evolution of Burmanniaceae (Dioscoreales) based on nuclear and mitochondrial data. American Journal of Botany 93: 1684–1698.

Mignouna HD, Abang MM, Asiedu R and Geeta R (2009) Dioscorea, true yams – a biological and evolutionary link between eudicots and grasses. In: Emerging Model Organisms. Cold Spring Harbor: Cold Spring Harbor Protocols.

Zhang L, Barrett SCH, Gao J‐Y et al. (2005) Predicting mating patterns from pollination syndromes: the case of “sapromyiophily” Tacca chantrieri (Taccaceae). American Journal of Botany 92: 517–524.

Further Reading

Dahlgren RMT, Clifford HT and Yeo PF (1985) The Families of the Monocotyledons. Berlin: Springer.

Huber H (1998) Dioscoreaceae. In: Kubitzki K (ed.) The Families and Genera of Vascular Plants, pp. 216–235. Berlin: Springer.

Stevens PF (2001 onwards) Angiosperm Phylogeny Website. Version 9, June 2008 [and more or less continuously updated since]. http://www.mobot.org/mobot/research/apweb/orders/dioscorealesweb.htm

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How to Cite close
Geeta, R(Apr 2011) Dioscoreales (Yams and Allies). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003704.pub2]