Inferring nativity and biogeographic affinities of central and marginal populations of Froelichia floridana (Amaranthaceae) from Inter-Simple Sequence Repeat (ISSR) markers1

and southeastern United States. We analyzed the biogeographic patterns of this species to answer a series of questions regarding its historical dispersal and recent range expansion, and the relationships of a disjunct population in southern Ohio using a combination of genetic analyses based on Inter-Simple Sequence Repeat markers (ISSR) and herbarium studies. Amounts of genetic diversity showed a marked reduction in marginal populations in the far north and northeast of the species range, corresponding to areas where herbarium records show the species has become naturalized during the past 100 years. Our analysis suggests the recognition of three biogeographic lineages within this polymorphic species complex: a Great Plains lineage, an associated Midwestern Mississippian lineage, and an Atlantic Coastal Plain lineage. These lineages have been loosely recognized as taxonomic varieties: the western lineages as F. floridana var. campestris (Small) Fern., and the eastern lineage as F. floridana var. floridana (Nutt.) Moq.; however, our data suggest that the continued recognition of these varieties is not warranted. The disjunct population in Ohio, formerly believed to be a remnant of a once larger distribution and presently state-listed as a rare species, shows patterns of genetic diversity and differentiation comparable to recently established marginal populations in other states, and was most likely derived from the Great Plains or Midwestern lineages.