Dioscoreales is an Order in the Monocots in the Apg3 classification. It has 3 families: Dioscoreaceae, Nartheciaceae and Burmanniaceae. Petrosaviaceae is placed in its own Order Petrosaviales in the Apg3 classification. It is a group of 2 genera that are difficult to place.
It is not easy to be definite about this order due to lack of information in homeopathy. In the Plant theory Petrosaviaceae is included in Dioscoreales. Trichopus is placed in its own family Trichopodiaceae, as in the earlier classifications. Tacca is placed in its own family Taccaceae, as in the earlier classifications.
Dioscoreaceae: 6 genera; Dioscorea, Epipetrum, Rajania, Stenomeris, Tacca, Trichopus.
Nartheciaceae: 5 genera: Aletris, Lophiola, Metanarthecium, Narthecium, Nietneria
Burmanniaceae: parasitic plants; 17 genera: Afrothismia, Apteria, Burmannia, Campylosiphon, Cymbocarpa, Desmogymnosiphon, Dictyostega, Geomitra, Gymnosiphon, Haplothismia, Hexapterella, Marthella, Miersiella, Oxygyne, Scaphiophora, Thismia, Tiputinia.