This southeastern species occurs mostly in the central and lower Mississipp Valley, extending only locally to Atlantic states. It usually occurs in thin submesic to subhydric woods on base-rich soils, usually on lowlands but sometimes on seasonally damp ledges or in upland seeps. It is often concentrated in woods along edges or where is some other history of disturbance. The name H. caroliniana (L.) Herbert has been misapplied to this species, according to FNA 26 and W. Hymenocallis and its relatives are remarkable showy plants, centered in tropical America. They have unusually large flowers (pollinated by large moths) and large seeds. Whitehead & Brown (1940) stated that, in occidentalis: "One of the striking features of the seed is that it undergoes continuous development, never experiencing a dormant period. This condition is referred to as 'after-ripening' and is considered as intermediate between true vivipary and dormancy." Dispersal of seed is not well documented but may involve vertebrates; see also Markwith et al. (2009). Hymenocallis includes tetraploids at the base of its phylogeny: 2n = 46, but 2n = 40 in occidentalis. They are distant allies of cultivated Eurasian plants such as Lycoris (2n = 22 basally), Leucojum (22) and Narcissus (14).