With over 250 species, Eriogonum is one of North America's largest plant genera. Species occupy a wide range of elevations and habitats, and many occur on unusual, inhospitable soils such as serpentine. In California, over 25 species grow on serpentine, and about half are thought to be endemic to these ultramafic soils. Eriogonum subgenus Oligogonum is especially well represented. With a focus on Oligogonum, objectives of our ongoing study are to evaluate the existing classification and reveal the number of evolutionary shifts to serpentine soils. We employ a reduced-representation method, double-digest restriction site-associated DNA, for sequencing. Analysis of these data suggest the polyphyly of E. umbellatum, the presence of multiple currently unrecognized species, and multiple transitions to serpentine soils.