This monotypic genus occurs in thin lowland woods on fertile terraces from Wis. and Iowa to Ohio, with disjunct records in Pa. and Va. (K, W). Its range is curiously similar to that of Hasteola suaveolens, although not extending so far south. In Ky. Napaea has been reported from "a single station on the bank of Gun Powder Creek" (BOON) by Nelson (1919). Although no coll. has been located, this record is reasonably reliable considering that it is known nearby at several sites in sw. Ohio. Typical associates in Ill. include Ageratina altissima, Amorpha fruticosa, Campanulastrum americanum, Celtis occidentalis, Elymus virginicus (sensu lato), Rudbeckia laciniata, Silphium perfoliatum and Verbesina alternifolia (Swink & Wilhelm 1994). As with Sida hermaphrodita, which occurs in similar habitats further south, herbivores may play a role in restricting abundance. Both species are highly palatable for generalist mammalian herbivores, and attempts to grow Napaea in FAYE have been largely thwarted by the virtually complete consumption of leaf parenchyma during May-June by small unknown insects.