Data from: Genetic and ecotypic differentiation in a Californian plant polyploid complex (Grindelia, Asteraceae)

Studies of ecotypic differentiation in the California Floristic Province
have contributed greatly to plant evolutionary biology since the
pioneering work of Clausen, Keck, and Hiesey. The extent of gene flow and
genetic differentiation across interfertile ecotypes that span major
habitats in the California Floristic Province is understudied, however,
and is important for understanding the prospects for local adaptation to
evolve or persist in the face of potential gene flow across populations in
different ecological settings. We used microsatellite data to examine
local differentiation in one of these lineages, the Pacific Coast
polyploid complex of the plant genus Grindelia (Asteraceae). We examined
439 individuals in 10 different populations. The plants grouped broadly
into a coastal and an inland set of populations. The coastal group
contained plants from salt marshes and coastal bluffs, as well as a
population growing in a serpentine grassland close to the coast, while the
inland group contained grassland plants. No evidence for hybridization was
found at the single location where adjacent populations of the two groups
were sampled. In addition to differentiation along ecotypic lines, there
was also a strong signal of local differentiation, with the plants
grouping strongly by population. The strength of local differentiation is
consistent with the extensive morphological variation observed across
populations and the history of taxonomic confusion in the group. The
Pacific Clade of Grindelia and other young Californian plant groups
warrant additional analysis of evolutionary divergence along the steep
coast-to-inland climatic gradient, which has been associated with local
adaptation and ecotype formation since the classic studies of Clausen,
Keck, and Hiesey.