The main genera included in the tribe before the start of the 21st century were "Schoenocaulon", "Stenanthium", "Veratrum", "Melanthium" (often included in "Veratrum") and "Zigadenus" s.l. The last genus contained about 20 species when broadly defined and lacked very distinctive morphological features. Various genera were constructed between 1837 and 1903 to divide up "Zigadenus", including "Amianthium" (Gray, 1837), "Anticlea" (Kunth, 1843) and "Toxicoscordion" (Rydberg, 1903). Only the first of these gained broad acceptance in the 20th century (e.g. the "Flora of North America" recognizes only "Amianthium" and "Zigadenus"). A study in 2001 based on both nuclear and plastid gene sequences led to the conclusion that the broadly defined "Zigadenus" was polyphyletic; in particular the genera "Schoenocaulon" and "Veratrum"-"Melanthium" were nested inside it. Monophyletic groups could be produced by splitting "Zigadenus" into five genera (assuming "Amianthium" to have been included): "Amianthium", "Anticlea", "Stenanthium", and "Toxicoscordion", leaving only "Zigadenus glaberrimus" in "Zigadenus". Although the reorganization was done primarily on the basis of molecular grounds, it is supported by morphological and distributional considerations. The cladogram below shows phylogenetic relationships in the Tribe Melanthieae; shaded names represent nodes which contain species formerly placed in the broadly defined "Zigadenus".