Understanding species limits in recent radiations is often difficult because sufficient time may not have elapsed since speciation to allow for the accumulation of unique species-specific traits. However, because population genetic markers evolve rapidly, patterns of genetic structure based on these markers can often discern genetically isolated population groups, even when other markers, such as DNA sequences, can not. In this study, we analyzed patterns of genetic structure based on microsatellites in Conradina and identified a group of plants in Dunns Creek State Park (Putnam County, Florida) that are genetically divergent from all other described Conradina species. We then carried out a morphological study that revealed several unique characters in these populations, most notably thin-walled unicellular hairs, epidermis features, and larger calyces. Because these populations are genetically and morphologically diagnosable from all other Conradina species, we thus consider them to be specifically distinct, and name this taxon Conradina cygniflora. Conradina cygniflora is endemic to Dunns Creek State Park in south-central Putnam County, Florida, where it occupies nine tightly-clustered sites that probably form around two to four self-sustaining populations. Due to its extremely limited geographic distribution and few individuals, we recommend that Conradina cygniflora be listed as federally endangered.