An agamic complex of 20- and 10-stamen, black-fruited hawthorns (Crataegus subg. Sanguineae, sect. Douglasianae) occurs in western North America, with a 10-stamen taxon disjunct the upper Great Lakes basin. Here, we recircumscribe 20-stamen taxa at core this (C. ser. Douglasianae). This is needed order to distinguish between presumptively ancestral diploid its allo- autopolyploid derivatives, a...
