ASTRAGALUS MOLYBDENUS S.L. (LEGUMINOSAE) - HIGHER TAXONOMIC RELATIONSHIPS AND IDENTITY OF CONSTITUENT SPECIES

The Rocky Mountain Astragalus molybdenus s.l. comprises A. molybdenus from Colorado, A. shultziorum from Wyoming, and A. lackschewitzii sp. nov. endemic to Montana. These three species are determined to be clos ely related to the species of Astragalus sect. Polares. Section Minera les, formerly a monotypic taxon that accommodated A. molybdenus in the Phacoid Phalanx next to sect Astragalus, is now synonymized with sect . Polares. Supporting evidence comes from morphometric and cladistic a nalysis of morphological and chloroplast DNA restriction site data, an d is consistent with findings reported elsewhere on sequence variation of the internal transcribed spacers that flank 5.8S nuclear ribosomal DNA. A previously overlooked attribute of A. molybdenus s.l. (the mat ure pod, which is deciduous from a marescent, ventrally ruptured calyx ) is used to pinpoint the relationships of this species group to the p iptoloboid Homalobi subgroup of Neo-astragalus. Additionally, chloropl ast DNA sequences are exceptionally divergent among populations, on th e order of 1.5-2.0%, and this evidence is used in part to support the recognition of three constituent species within A. molybdenus s.l.