A New Species of \u3ci\u3eEuphorbia\u3c/i\u3e Subgenus \u3ci\u3eChamaesyce\u3c/i\u3e Section \u3ci\u3eAlectoroctonum\u3c/i\u3e (Euphorbiaceae) From Limestone Hills of Wayne County, Mississippi

As part of a project to document the vascular flora of Wayne County, Mississippi, an unusual Euphorbia, which keys to the Euphorbia corollata complex, was encountered in mature hardwood forests in limestone regions. Unlike typical E. corollata and E. pubentissima, these individuals have long petioles (0.4–1.2 cm), oval to ovate leaves, short stature, small cyathia, small seeds, and a different phenology. In order to test species boundaries, morphological character differences were explored using principal component analysis (PCA), and additional characters were gathered from plastid (rpL16) and nuclear (ITS) DNA data of the unusual individuals as well as of E. corollata, E. pubentissima, and several other species of Euphorbia subgenus Chamaesyce section Alectoroctonum. The PCA indicates that the individuals are morphological outliers, and phylogenetic analyses of the DNA data indicate that the individuals have a unique haplotype different from E. corollata or E. pubentissima and are rather more closely related to E. mercurialina, a species not in the E. corollata complex but which occurs in similar mesic habitat in eastern Tennessee and neighboring Alabama, Georgia, and Kentucky. These data support the hypothesis that these unusual individuals represent a new species. Neither the PCA nor the phylogenetic analysis of DNA data reveals any differences between E. corollata and E. pubentissima