The taxonomic history of Claytonia lanceolata is fraught with confusion. Poor preservation of diagnostic characteristics on museum specimens and incomplete original descriptionsmade from limited reference material have resulted in inadequate characterization of morphological features and geographic distributions, particularly for plants in more xeric areas of California. In this paper, we investigate populations previously thought to belong to C. lanceolata and provide an updated taxonomy for Californian taxa based largely on morphological observations and geographic records. These data are corroborated by evidence of genetic polymorphisms and ecological divergence. Claytonia obovata was synonymized with C. lanceolata in 1966 and remained unrecognized until now because previous treatments misinterpreted morphological variation in C. lanceolata s. s. Claytonia peirsonii is a new combination for a species comprising four subspecies endemic to the Desert Southwest, three of which are new to science. Two new species are described here: Claytonia panamintensis, known in California only from the Panamint Mountains but ranging morewidely across southern Nevada, and Claytonia serpenticola. The latter species shares a similar geographic rangewith C. obovata in the Klamath-Siskiyou region of northern California and southwestern Oregon, and these two occur in close sympatry through much of their respective distributions. We also provide molecular evidence to support retention of the name C. lanceolata for populations in California that do not fall into any of the aforementioned new species or combinations. Taxa accepted in this paper are best distinguished from each other by their habitat (many are apparently edaphic endemics), betalain pigmentation, inflorescence architecture, and morphology of cauline leaves, subterranean stems, and flowers.