Two cryptic species of California mustard within Caulanthus lasiophyllus

Cryptic species are evolutionarily distinct lineages lacking distinguishing morphological traits. Hidden diversity may be lurking in widespread species whose distributions cross phylogeographic barriers. This study investigates molecular and morphological variation in the widely distributed Caulanthus lasiophyllus (Brassicaceae) in comparison to its closest relatives.

Fifty-two individuals of C. lasiophyllus from across the species' range were sequenced for the nuclear ribosomal internal transcribed spacer region (ITS) and the chloroplast trnL-F region. A subset of these samples were examined for the chloroplast ndhF gene. All 52 individuals were scored for 13 morphological traits, as well as monthly and annual climate conditions at the collection locality. Morphological and molecular results are compared with the closest relatives-C. anceps and C. flavescens-in the "Guillenia Clade." To test for polyploidy, genome size estimates were made for four populations.

Caulanthus lasiophyllus consists of two distinct lineages separated by eight ITS differences-eight times more variation than what distinguishes C. anceps and C. flavescens. Fewer variable sites were detected in trnL-F and ndhF regions, yet these data are consistent with the ITS results. The two lineages of C. lasiophyllus are geographically and climatically distinct; yet morphologically overlapping. Their genome sizes are not consistently different.

Two cryptic species within C. lasiophyllus are distinguished at the molecular, geographic, and climatic scales. They have similar genome sizes and are morphologically broadly overlapping, but an ephemeral basal leaf character may help distinguish the species.