Revision of Fothergilla (Hamamelidaceae), including resurrection of F. parvifolia and a new species, F. milleri

Abstract

Fothergilla is a small genus of deciduous shrubs native to the southeastern United States that depending on circumscription comprises two to four species. Recent treatments recognized only two species in the genus: F. gardenii (tetraploid) and F. major (hexaploid). Until recently, no diploid taxon of Fothergilla was known. However, recent investigations identified a number of diploid populations in Alabama, Florida, Georgia, and South Carolina. A subsequent phylogenomic analysis showed that the diploids segregated into two, well-supported lineages, corresponding to largely allopatric populations. A re-examination of the morphology of diploid plants, in combination with the genetic evidence, has led us to the recognition of two species of diploids in the genus – a resurrected F. parvifolia and a new species (F. milleri W.D. Phillips & J.E. Haynes, sp. nov.) – bringing the total number of recognized species in Fothergilla to four. A revised taxonomic treatment of the genus is provided.