Data from: Undescribed species diversity in Brewer’s Jewelflower illuminates potential mechanisms of diversification associated with serpentine endemism

Premise of study: Documenting species-level diversity is a fundamental
goal of biology, yet undescribed species remain hidden even in
well-studied groups.  Inaccurate delimitation of species
boundaries can limit our understanding of ecological and evolutionary
processes and patterns of biodiversity, and may further impede
conservation and management efforts. Methods: We utilized an integrative
approach, combining techniques from speciation biology, molecular
phylogenetics, and geometric morphometrics to assess diversity in the
Californian serpentine endemic Streptanthus breweri (Brewer’s
Jewelflower).  We assessed reproductive isolation resulting from
flowering time differences, mating system differences, and interfertility
among four distinct geographic clusters of S. breweri that span the
geographic range of the species.  We generated a gene tree based
on the ribosomal DNA internal transcribed spacer region (ITS), a
diagnostic species-level marker for this clade of jewelflowers, and
additionally quantified leaf morphology in plants grown under common
conditions. Key Results: Four geographic clusters of S. breweri in
northern California represent not a single species, but instead a species
complex of at least three putative species.  Independent data
associated with Biological, Phylogenetic, and Morphological Species
Concepts support these conclusions.  Conclusions: This work
illustrates that latent biodiversity may be concealed even in well-studied
groups and underscores the contribution of edaphic endemism generally, and
serpentine endemism specifically, to California’s rich plant
biodiversity.  The existence of unrecognized species diversity
within the S. breweri species complex highlights multiple factors,
including 1) the spatial context of geologic discontinuities, 2) a selfing
mating system, and 3) differential selection pressures across
discontinuous specialized habitats as potential drivers of evolutionary
divergence on serpentine.