Molecular Phylogenetics and Taxonomy of the Genus Boechera and Related Genera (Brassicaceae: Boechereae)

Boechera (Brassicaceae) is a diverse genus of +/- 70 sexual diploid species and numerous apomictic hybrids concentrated in western North America. It is the largest genus in tribe Boechereae, which also includes seven other small genera. Boechera is closely related to Arabidopsis and is becoming a model genus for diverse studies, focusing particularly on apomixis and hybrid speciation. As part of an ongoing effort to clarify the taxonomy of the group, we present phylogenetic analyses of Boechereae, including all genera of the tribe and most of the sexual diploid species of Boechera. Ten loci are used, including two plastid loci, nrDNA ITS, and seven low-copy nuclear loci. These analyses indicate that Boechera, as currently circumscribed, is polyphyletic, comprising three main clades. Eastern North American species previously assigned to Boechera form a distinct clade with the Asian taxon Borodinia macrophylla and are herein transferred to the genus Borodinia, resulting in seven new combinations (Borodinia burkii, Borodinia canadensis, Borodinia dentate, Borodinia laevigata, Borodinia missouriensis, Borodinia perstellata, and Borodinia serotina). Boechera repanda, a morphologically aberrant species endemic to the Sierra Nevada, is recognized in the new genus Yosemitea (as Yosemitea repanda). A primarily western North American clade comprising all remaining species is strongly supported and retains the name Boechera. Although resolution within Boechera sensu stricto is limited, a number of well-supported clades are identified.