The Dioscoreales are an order of monocotyledonous flowering plants in modern classification systems, such as the Angiosperm Phylogeny Group and the Angiosperm Phylogeny Web. Within the monocots Dioscoreales are grouped in the lilioid monocots, where they are in a sister group relationship with the Pandanales. The Dioscoreales must contain the family Dioscoreaceae which includes the yam (Dioscorea), some species of which are an important food source in many regions. Older systems tended to place all lilioid monocots with reticulate veined leaves (such as Smilacaceae and Stemonaceae together with Dioscoraceae) in Dioscoreales. As currently circumscribed by phylogenetic analysis using combined morphology and molecular methods, Dioscreales contains many reticulate veined vines in Dioscoraceae, it also includes the myco-heterotrophic Burmanniaceae and the autotrophic Nartheciaceae. The order consists of three families, 22 genera and about 850 species.