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.