A contribution to the taxonomy and phylogeny of Oxytropis section arctobia (Fabaceae) in North America

Abstract

North American species of Oxytropis section Arctobia are reviewed through herbarium vouchers, scanning electron microscopy of seed coats, and phylogenetic analysis of sequence data to test the validity of the circumscription of section Arctobia as previously proposed. Morphologically, section Arctobia is characterized by few flowered inflorescences, few leaflets per leaf, and a mainly cushion-like habit. The micro-morphological data found considerable infraspecific variation in seed coat patterns. Sequence data from the nuclear TRPT, CNGC5, GA3ox1 genes and the plastid matK gene were used to infer phylogenetic relationships among members of section Arctobia. Analyses using maximum parsimony, maximum likelihood and Bayesian inference of these sequences resulted in a phylogeny that unambiguously supports the monophyly of Oxytropis. None of the infrageneric subdivisions of Oxytropis were supported by our genetic analyses. Section Arctobia was found nested within species of section Orobia, Glaeocephala, and Baicalia. However, TRPT and matK sequence data support Oxytropis arctobia as a distinct species, which has previously been included under Oxytropis nigrescens under the North American treatment. Here eight species are recognized in section Arctobia for North America and a lectotype of Oxytropis arctobia is selected based on herbarium specimens.