This widespread eastern species is generally distinct from perplexum and glabellum, but there are occasional (<1%) intermediates (Isely 1983). There is also evidence from other states for occasional hybridization with other species (Y). Included here are records of var. pubens Torr. & Gray. Although plants usually have sparse pubescens (versus moderate to dense in glabellum and perplexum), there is much variaton in pubescence density and type (appressed, spreading or hooked). Leaflet blades, at least the central, have relatively narrow shape (Y): L/W = mostly 3-8 (versus 1.5-4). Unusually narrow leaflets, only 6-10 mm wide, occur locally in Ky. and may be associated with warmer drier environments (e.g. on gravelly hills in TRIG).