This largely diploid species (2n = 24) occurs mostly in the Ozark region and ne. La., in the southern Interior Low Plateaus and on the southern Cumberland Plateau (FNA 26). However, there are also remarkable disjunctions in se. Ohio (Scioto Co.), discovered by E.L. Braun in 1964, and then in ne. Ky. by Cusick (1989). Ky. localities are all north of the Kentucky Rv. watershed. E. rostratum differs from americanum as follows (FNA 26, W): mature capsules mostly 15-25 mm long (versus 12-15 mm), ellipsoid-obovoid (versus obovoid), distinctly beaked at the apex (versus truncate, rounded or apiculate); auricles of petals well-developed at base, each encircling a filament (versus small, not encircling); flowers somewhat erect at anthesis with spreading petals (versus nodding with strongly reflexed petals); anthers yellow (versus yellow to brown).