Sisyrinchium sarmentosum is a rare endemic plant of the middle Cascade Mountains of Oregon and Washington, with 16 known populations, each estimated to be 50 to 8000 individuals. I have examined the genetic diversity of a representative subset of populations using random amplified polymorphic DNAs (RAPDs). Five visited populations originally reported to be less than 100 plants were extirpated or intermediate with S. idahoense. From the remaining 7 populations sampled, three distinct groups emerged, conforming to the metapopulation model of species diversity. Oregon and Washington sites showed differences in the distribution of genetic diversity within populations, and groups are correlate geographically. The five largest populations appear to be thriving, in spite of over a century of cattle grazing and habitat alteration. Conservation should emphasize not only the protection of these large populations from hybridization and habitat loss, but also encourage establishment and maintenance of smaller satellite populations. Preliminary chloroplast sequence data indicates that S. sarmentosum is more closely related to S. angustifolium and S. albidum, species of the east coast, than to the local widespread cogener, S. idahoense, favoring the hypothesis that S. sarmentosum is part of a Columbia River Gorge glacial refugia, rather than being of recent origin.

Key words: genetic diversity, Iridaceae, metapopulation, RAPDs, rare endemic, Sisyrinchium sarmentosum