The development of conservation policy for rare plant species is informed by largescale patterns of distribution and abundance as well as the processes that generate them. I collected data on 224 rare vascular plants in the Southeastern U.S. to characterize patterns of rarity at ecoregional scales, among broad habitat types, and with respect to taxonomic group size. Rare species diversity is highest in Appalachian/Blue Ridge Forests and Southeastern Conifer Forests ecoregions. Most rare plants are concentrated in woodland and glade habitats and larger taxonomic groups. A case-study experimental approach was adopted to explore the significance of reproductive biology in the persistence of a globally imperiled Southeastern endemic plant, Ptilimnium nodosum. The species has a phenologically regulated mixed mating system dependent on insect-mediated pollination. Moderate reproductive output and high seed germinability suggest environmental conditions, not mating system, play a critical role in regulating the species’ distribution and abundance, and favor high immediate fitness gained by vegetative reproduction.