Yams reclassified: a recircumscription of Dioscoreaceae and Dioscoreales

Analyses of morphological and molecular characters for Dioscoreales Hook. f. (Chase al., 1995b; Caddick al., 2000a; Caddick & al., 2002) have redefined the order, which now comprises three families, Burmanniaceae, Dioscoreaceae, and Nartheciaceae. Since recent analyses of morphological and molecular data sets (Caddick & al., 2002) have indicated well-supported relationships within Dioscoreaceae R. Br., a formal reclassification of the family is presented here. Dioscoreaceae now contain four distinct genera, Dioscorea, Stenomeris, Tacca (previously in Taccaceae), and Trichopus. The Malagasy endemic Avetra sempervirens is close sister to Trichopus zeylanicus, and is here reclassified as a second species of this genus. The dioecious Dioscoreaceae genera, Borderea, Epipetrum, Nanarepenta, Rajania, Tamus, and Testudinaria, are nested within Dioscorea in phylogenetic analyses (Caddick & al., 2002), and are therefore sunk into it.