Dioscoreales are a small but systematically and economically significant order of monocotyledons. The most diverse and important member is the yam genus, Dioscorea L., a source of dietary starch at macroeconomic to rural community levels. Other species of Dioscorea provided the chemical basis of corticosteroid drugs and oral contraceptives. Ally families comprise the unusual, largely achlorophyllous (heteromycotrophic) Burmanniaceae and the relatively...