The Genus Salix (Salicaceae) in the Southeastern United States

The taxonomy of Salix in the southeastern United States was studied in the field and herbarium. Twelve species and one variety of native willows are recognized and seven species and one subspecies are shown to be introduced and naturalized. A quantitative study of variation in S. caroliniana and S. nigra supported species rank for these entities and showed that infraspecific variation was too diffuse to warrant taxonomic recognition. Salix humilis has been shown to consist of two varieties: var. humilis and var. microphylla. Salix floridana is an endemic species that belongs in sect. Humboldtiana. It may be a Tertiary relict that survived the Pleistocene glaciation in northern Florida. The phytogeographical patterns displayed by this and other species of Salix are related to Pleistocene events. During the Full-Glacial some northern willows presumably extended far south of their present ranges and some northern species had their ranges fragmented. Some northern species occur here now as peripheral species (S. amygdaloides, S. bebbiana, S. discolor, and S. lucida); others, such as S. eriocephala, left major disjunct populations behind following deglaciation. The disjunct Ozark population of S. caroliniana may also be related to these events, or it may have had its origin in Tertiary times. The recognition of these taxa of Salix is aided by keys to staminate, pistillate, and vegetative specimens, detailed descriptions, and comparison with related and similar species. Taxonomy, nomenclature, variation, and hybridization of each native species are discussed. Each species is illustrated; range maps are also provided.