Flora of North America species comparison

Variety hispida occurs in the mountains and hills of western Maryland and Virginia, eastern West Virginia, and Surry County, North Carolina, where var. americana and Heuchera pubescens overlap; it is intermediate between var. americana and H. pubescens in floral characters. Variety hispida was confused with H. richardsonii for almost a century, beginning in 1849 when Gray reduced H. richardsonii to synonymy under H. hispida, after some seeds of H. richardsonii germinated among H. hispida plants in a labeled plot and later replaced them (C. O. Rosendahl et al. 1933).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Variety hirsuticaulis occurs in a band from Oklahoma to Michigan, where var. americana and Heuchera richardsonii overlap; it is intermediate between those taxa in floral characters but is densely long stipitate-glandular like H. richardsonii. It is probably the result of introgression from H. richardsonii from as long ago as the Pleistocene migrations. Data from a breeding study involving the two species showed a tendency for the shorter hypanthium of var. americana to dominate in the artificial hybrids between H. americana and H. richardsonii (E. F. Wells 1979).

(Discussion copyrighted by Flora of North America; reprinted with permission.)