The largest of four Loteae genera, Lotus comprises approximately 200 species of leguminous herbs and shrubs distributed throughout the eastern and western hemispheres. In western North America, species of Lotus have been categorized into one of three subgenera: Acmispon, Hosackia and Syrmatium. Morphological features distinguishing these subgenera include a combination of dehiscent fruits and gland-like stipules (Acmispon), dehiscent fruits and scarious stipules (Hosackia), or simply, indehiscent fruits (Syrmatium). Acmispon is further subdivided into sections Microlotus and Simpeteria to distinguish between plants that do (Simpeteria) or do not (Microlotus) have a penicillate stigma. Although species characterizing each subdivision are morphologically cohesive, it is unclear whether their morphological similarities arose once or multiple times during the evolution of the genus. It is also unclear how these subgenera are related to one another phylogenetically. Further, some species bear a strong resemblance to members of the Coronilleae, a closely allied Old World tribe consisting of six genera and distinguished primarily by their jointed fruits. Preliminary parsimony analysis of the nrDNA ITS region demonstrates that: (1) Syrmatium is monophyletic, (2) the indehiscent fruit type of Syrmatiumis synapomorphic, having arisen once in the genus; (3) Acmispon is likely monophyletic and appears to form a clade sister to Syrmatium; (3) Hosackia is polyphyletic, with scarious stipules arising independently at least two times; and (4) Coronilla is not monophyletic, but is nested within Lotus, with different species more closely allied to either Hosackia, Acmispon or Old World Lotus, than to one another. This suggests that the jointed fruit type characterizing at least one member of the Coronilleae has arisen multiple times within Lotus. Additional phylogenetic studies including other genera from both the Loteae and Coronilleae will be necessary to evaluate overall relationships and current delimitation of the two tribes.

Key words: Coronilla, Fabaceae, ITS region, Lotus, nrDNA