This is a largely midwestern species of thin submesic to subxeric woods and grassland transitions on more or less base-rich soils. It is considered threatened or endangered in all states where it has been recorded, except perhaps Mo. and Ill. (NS). West of the Mississippi Rv., there is a remarkable series of disjunct localities, from c. Miss. to c. Ohio (K). The few Ky. records are mostly from the former Big Barrens region, plus a few from rocky woods of the central Bluegrass, including the FRAN site with Trifolium kentuckiense. Small precarious populations in JEFF (Cherokee Park) and JESS (Scotts Grove) have persisted in thin rocky woods with dense alien vines (Akebia, Euonymus, Hedera), but appear able to recover after appropriate moderate disturbance, along with graminoids such as Elymus hystrix and Carex oligocarpa. P. americana is unusual among eastern Apiaceae in its ability to spread vegetatively from tuberously thickened multistelic roots, which are conic-ovoid structures ca. 1-2 cm long that send out runners ca. 5 cm long during Oct to May (Baskin & Baskin 1993). These roots are highly edible for mammalian herbivores and humans--the genus was known to some native people as "yampah" (Anderson 1997, Moerman 2009). One wonders if a new carrot-like commercial vegetable could be bred from wild plants. It is likely that rooting by hogs has greatly reduced the original populations. Flowers are produced in late May to Jun, and plants senesce above ground in Jul.