A Revision of the Genus Heuchera (Saxifragaceae) in Eastern North America

Wells, Elizabeth

ABSTRACT: The eastern species of Heuchera fall into two natural groups on the basis of phenological, morphological, and breeding data. Three spring-blooming species (H. pubescens, H. richard sonii, and H. longiflora) formerly belonging to section Heruchea are placed in subsection Americanae of section Heuchera with H. americana and H. caroliniana. These species possess striking differences in floral characteristics but are vegetatively quite similar; they do not have genetic barriers to hybrid ization and several species in this group are only weakly isolated by geographical and ecological barriers. Natural hybridization involving three species (H. americana with H. pubescens and H. richardsonii) is suspected. Among the summer-blooming species H. parviflora is removed from subsection Micranthae to subsection Villosae within section Heuchera. These species are very similar in floral characters but are vegetatively and ecologically distinct; they apparently do not hybridize in the wild, even though artificial hybrids between them are moderately fertile. The first chromosome counts for H. caroliniana and H. longiflora (both n = 7) are reported. The treatment includes descriptions for all taxa and illustrations for all species. A key to the species and varieties as well as distribution maps are provided. All numbered collections examined are listed in an index.