Cohen and Schenk (2021) Data from: Investigating phylogenetic placement and species-level relationships in a recent radiation of Mentzelia section Bartonia (Loasaceae) from the Mojave Desert

Understanding species level relationships is a central goal in systematic
botany; however complexes of closely related and morphologically similar
species often pose considerable challenges to that goal. The North
American west is home to many notable genera that notoriously have
difficult species complexes (e.g., Astragalus, Eriogonum, Penstemon).
Mentzelia section Bartonia (Loasaceae) is a recently evolved and diverse
clade that occurs across the North American west. Phylogenetic studies
have resolved many relationships, but the relationships within a species
complex of perennial, subshrub species that occurs in the Mojave Desert,
Great Basin, and Colorado Plateau remains elusive. This arid-adapted
clade, which is referred to as the Mojave clade, has significant
conservation implications, due to three narrowly endemic
species:  Mentzelia polita and Mentzelia tiehmii are state
listed, and Mentzelia leucophylla is federally listed. Species
relationships within the Mojave clade are not fully understood.
Populations of Mentzelia oreophila from California and Nevada, for
example, are not monophyletic. We generated restriction site associated
DNA sequence data (RADSeq) to address evolutionary relationships in the
Mojave clade. Our results corroborated previous studies in continued
recognition of Mentzelia polita, Mentzelia leucophylla, and Mentzelia
tiehmii; however, Mentzelia oreophila was recovered in three clades that
includes a California clade, a Nevada clade, and one with Mentzelia
puberula. Incomplete lineage sorting and hybridization might have
generated conflicting phylogenetic signal between Mentzelia oreophila and
Mentzelia puberula. Increasing population level sampling will aid in
species delimitation and further help to understand how gene flow and/or
hybridization is influencing population level dynamics in the Mojave
Desert.