California's vernal‐pool mousetails ( <i>Myosurus</i> , Ranunculaceae): Phylogenetic analysis of ddRADseq data, hybridization tests, and species delimitation

Abstract We used double‐digest restriction site‐associated DNA sequencing (ddRADseq) to investigate the evolutionary relationships of Myosurus in California. Our phylogenetic analysis reveals a deep divergence between two major subclades, “Longipes” and “Brevipes,” so named because members of the former have scapes generally surpassing the leaves, while those of the latter have shorter scapes (or the flowers and fruiting spikes are ± sessile). Bayesian species delimitation under the multispecies coalescent consistently found 10 species in our sample. European M. minimus (represented by one sample) is placed in the “Longipes” subclade, but evidently not closely related to the Californian taxa. Also in the “Longipes” subclade, M. filiformis (based on M. minimus var. filiformis ) is resolved as sister to a newly discovered lineage, M . “collinus.” Within the “Brevipes” subclade, M. apus (based on M. minimus var. apus ) is evidently a rare species restricted to coastal Southern California and northwestern Baja California. Plants previously assigned to M. apus from the Central Valley and Carrizo Plain are resolved in two other newly discovered lineages: M . “vallicola” and M . “digitiformis.” Classification of the plants from Riverside County remains uncertain due to a gap in sampling. Myosurus clavicaulis , first described from southeastern Oregon, is resolved as a distinct species ranging from Northern California and more widely in the Pacific Northwest (east of the Cascade Range). A strong signal of genetic admixture was found in many of our samples, consistent with a model of predominant self‐pollination and occasional hybridization as drivers of adaptive divergence.