A phylogenetic and monographic study of Oxypolis, Ptilimnium, and closely related genera (Apiaceae)

A phylogenetic and monographic study of Oxypolis, Ptilimnium, and closely related genera in the North American endemics clade of tribe Oenantheae (Apiaceae) was carried out. Sequences from the nuclear ribosomal DNA internal transcribed spacer (ITS) region and the chloroplast DNA trnQ-5'rps16 and 3'rps16-5'trnK intergeneric spacer regions were used to estimate the phylogenetic relationships of Oxypolis, Ptilimnium, and closely related genera. The sequence data were analyzed using maximum parsimony, maximum likelihood and Bayesian methods. Results of the phylogenetic analyses showed that neither Oxypolis nor Ptilimnium was monophyletic. In the analyses, each genus was separated into two strongly supported clades that corresponded to differences in leaf morphology within the groups. While most species of Oxypolis and Ptilimnium have compound leaves, others share a unique leaf morphology known as rachis leaves. Rachis leaves are linear, terete, hollow, and septate and are equivalent to the rachis of a pinnately compound leaf in which the pinnae are not expressed. Fruit anatomical characters were explored and were also found to support these splits. Based on the analyses of the molecular data (ITS and cpDNA sequences) and the corroboration of morphological and fruit anatomical data, new circumscriptions for the genera Oxypolis and Ptilimnium were formalized. The two polyphyletic genera (Oxypolis and Ptilimnium) were split, two genera (Tiedemannia and Harperella) were resurrected, and new combinations were made. In addition to these generic level questions, the results of the phylogenetic analyses were used to examine a number of interspecific and infraspecific relationships within Oxypolis and Ptilimnium. As a result, the species P. texense was resurrected, P. ahlesii was placed in synonymy under P. capillaceum, and a case was made for the recognition of O. filiformis subsp. greenmanii. Also, a nomenclatural issue concerning the correct name for the species Oxypolis ternata was resolved. Finally, taxonomic treatments including keys, species and genus descriptions, and brief taxonomic discussions are presented for the following genera: Ptilimnium, Tiedemannia, Harperella, Limnosciadium, Cynosciadium, and Oxypolis. These treatments adopt the newly reinstated genera Harperella and Tiedemannia and include the closely related genera Cynosciadium and Limnosciadium. Treatments are written according to the Flora of North America Guide for Contributors for publication in Volume 13 of the Flora of North America series