This species occurs mostly in east-central states from the Ridge-and-Valley to the Ozarks (K); the only two congeners occur in central China (Flora of China 7: 284). Its range is somewhat fragmented, at least partly due to concentration in mesic woods on base-rich soils. Also, its abrupt western boundaries in sw. Ky. and sw. Tenn. suggest that past disturbances (perhaps frequent droughts and fires) may have restricted spread. In the central Bluegrass, Short (1828-9) noted: "This handsome plant, so abundant on the borders of the Ohio river, is comparatively rare in this neighbourhood ...in rich shaded situations." The chemistry of Stylophorum includes diverse isoquinoline alkaloids (Preininger 1986), which have generally adverse physiological effects in mammals. However, B. Palmer-Ball (pers. comm.) has observed sharp declines in an well-wooded area of JEFF with intensive deer browsing.