Packera paupercula is the most widely distributed and variable member of this newly segregated North American genus of herbaceous perennials. In addition to ecotypic and polyploid races, certain populations appear to intergrade morphologically with other regionally widespread Packera species with which they come in contact. Barriers to hybridization are low within the genus and introgression has been postulated. Because important taxonomic features are largely vegetative, this intergradation makes identification of taxa difficult. Recent field work, study of herbarium specimens, and chromosome counts suggest that certain Packera populations have been misidentified. Populations from the black prairie soils of Alabama, previously identified as P. anonyma, are probably P. paupercula. P. plattensis, a Great Plains tetraploid with a base chromosome number of 23, may have a much smaller distribution than previously thought: chromosome counts from putative disjunct eastern populations of this species have a base chromosome number of 22, like that of eastern P. paupercula. Some midwestern populations historically identified as P. plattensis represent a morphologically distinct stoloniferous entity, again with a base chromosome number of 22. Western P. paupercula appears to have a base chromosome number of 23, suggesting that it may not be closely related to eastern populations. Detailed field observations, a common garden experiment, multivariate analysis of morphological characters, chromosome counts, crossing experiments and soil analyses are complemented by an inter-simple sequence repeat (ISSR) analysis to infer inter- and intraspecific relationships among geographically isolated populations of Packera paupercula and its relatives, both widespread and restricted. New GIS-based distribution maps have been generated. Biogeography of the P. paupercula complex and recommendations for the recognition of taxa at specific and subspecific levels will be discussed.

Key words: Packera paupercula complex, Packera, Senecio