Five terete-leaved Talinum species occur in the Southeast on rock outcroppings. All are summer-flowering perennials with succulent leaves and ephemeral, rose-colored flowers. Talinum parviflorum (2n = 24) has tiny flowers that open late in the day and self-pollinate. This species is distributed in the central United States from Arkansas westward, but an outlier population, formerly named T. appalachianum, occurs in north Alabama. Talinum mengesii populations are predominantly diploid (2n = 24). This species, mainly distributed in northern Alabama, western Georgia and southeastern Tennessee, occurs on both granite and sandstone. Two enclaves of T. mengesii populations are isolated from the main distribution of the species and intervening outcrops have only T. teretifolium. Talinum teretifolium (2n = 48), distributed from Georgia to Pennsylvania, is an allopolyploid derived from T. mengesii and T. parviflorum. This conclusion is based on morphological, reproductive and biochemical evidence, and the recreation of the species from parental species. Talinum calcaricum (2n = 48) is endemic to limestone outcrops in Tennessee and Alabama. Evidence presented suggests a derivation from T. calycinum, which is distributed from Arkansas westward and has both diploid and tetraploid populations that grow on shale, sandstone or limestone. These two species differ in floral characteristics, but are 100% interfertile.