A New Ranunculus (Ranunculaceae) Species From South-Central Washington

A new Ranunculus species, Ranunculus basalticus Giblin sp. nov., is described from sagebrush-steppe and low elevation grassland areas of south-central Washington. The species is close in appearance to two sympatric Ranunculus species, the narrow endemic R. triternatus A.Gray and the broadly distributed R. glaberrimus Hook. However, discrete morphological, ecological, and distribution differences easily separate R. basalticus from these other species. The earliest record of R. basalticus dates to 2004 in the form of a digital photo, with subsequent voucher specimens first collected in 2009. Additional field collecting, along with photo submissions to iNaturalist, suggest that R. basalticus is a narrow endemic of Kittitas, Klickitat, and Yakima counties in Washington. It most commonly occurs in soil-stabilized basalt talus, for which the specific epithet refers. Although R. basalticus appears to have a narrow distribution, within its range, population sizes can exceed 100 plants. All currently documented populations are on public lands managed for multiple uses, though there appear to be no direct threats to these populations.