This is closely related to dentata, but tetraploid: 2n = 56 versus 28 as in most native Euphorbias. It presumably does not form frequent hybrids with dentata. Its lower leaf surfaces are more hispid pubescent; capsules are usually larger (4-4.8 mm wide versus 3.5-4 mm); and its seeds are more angled and more coarsely wrinkled-warty. See Y and W for detailed keys based on M.H. Mayfield (1997, Ph.D., Univ of Tex.). E. davidii has recently been resurrected as a species, but most previous manuals have not recognized it, even as E. dentata var. gracillima Millsp. It reportedly has a more northern range, but with much overlap. Initial data mapped here for Ky. were partly from K (citing Mayfield), but M. Brock has recently added several records from colls. at APSC.