Scientific Note: Neotypification of Ptelea mollis M.A. Curtis (Rutaceae)

Ptelea trifoliata L. (Rutaceae), in the sense of Bailey (1962) and Skornia et al. (2016), is a woody, understory species native to the southeastern and midwestern regions of the United States, as well as Mexico. It is one of two species initially described in Ptelea L. by Linnaeus (1753), the other being Ptelea viscosa L. [Dodonaea viscosa (L.) Jacq., Flora of China Editorial Committee 2007]. The circumscription of Ptelea in North America has been controversial, with authors variously recognizing a single species (Linnaeus 1753), three species (Bailey 1962), or 59 species (Greene 1906). Those adopting broader species circumscriptions, and thus fewer species, have variously recognized a number of subspecies and varieties within P. trifoliata (e.g., Bailey 1962: 5 ssp./10 var.; Skornia et al. 2016: 5 ssp./7 var.). Differences in taxonomic concepts are primarily the result of morphological heterogeneity and lack of understanding of genetic relationships in the group. Without a deeper understanding of the latter, circumscriptions are likely to continue to flux and remain unresolved. Typification of published names is critical to any effort to resolve taxonomic issues. We seek here to contribute to filling this gap, by addressing the typification of a name proposed by Reverend M.A. Curtis: Ptelea mollis M.A. Curtis (1849).