The genus Astragalus (Fabaceae) in North America is composed of nearly 400 species. Most Astragali in the western United States are annual or perennial herbs and are noted as "pioneer" species that grow in xeric habitats left vacant after the retreat of the last Ice Age. Astragalus oniciformis Barneby is a xerophyte of the sagebrush deserts of central Idaho. It is a narrow endemic of the upper Snake River Plains where it inhabits stabilized, aeolian sand deposits over Quaternary basalt flows. The demography of this species is well known, however the genetic variation of this species has never been documented. The objective of this study was to determine the levels and distribution of genetic variation within and among populations of Astragalus oniciformis. Several populations in the eastern portion of its range are isolated from the western populations by an eight mile long, inhospitable, basaltic lava flow. The eruption occurred 3600 years ago. The eastern populations will be analyzed to determine if they have significantly differentiated from the western, more contiguous populations. Inter-simple sequence repeats (ISSR) were chose as the marker used to assess genetic variability. Eight populations, chosen from throughout the distribution of the species, were selected for their accessibility, density of individuals, and large population size. Levels of genetic variation, genetic similarity, and degree of population differentiation will be investigated. Populations that exhibit high levels of genetic variation and/or differentiation will be identified as a priority for conservation.

Key words: Astragalus oniciformis, conservation genetics, ISSR, Snake River Plains