Diversity of the dwarf palmetto: A phylogeographic analysis of the North American coastal plain and investigation of stem polymorphism in Sabal minor (Jacq.) Pers.
Premise of the studySabal minor is considered one of two cold tolerant palm species, inhabiting riparian zones in temperate and subtropical North America. Ecologically it is often overlooked due to its short compact underground stem that makes it appear stemless, or acaulescent. However, across the central US Gulf Coast S. minor is polymorphic for trunk type, with some individuals identified as caulescent, bearing an above-ground trunk that can reach up to two meters in height. MethodsWe adopt a population genomics approach to characterize the genetic diversity of S. minor and to identify whether the caulescent and acaulescent forms of this temperate palm represent phenotypic variation within a single species. Key resultsThe caulescent and acaulescent forms are not reciprocally monophyletic, suggesting these two forms are phenotypic variants of a single species, S. minor s.l. Genetic clustering does not correspond to stem phenotype but rather reflects five discrete biogeographic clusters that span the native range. These geographic clusters indicate phylogeographic breaks along the Tombigbee River with a history that appears to be influenced by the delta of the Mississippi River. Two ecologically divergent populations, one in White Lake and another in Central Texas, show high genetic differentiation from surrounding populations indicating the presence of ecological barriers to gene flow. ConclusionsPopulation genetic structure of S. minor does not reflect stem morphotype (caulescence or acaulescence) supporting the current taxonomic recognition of one polymorphic species rather than two. However, populations of S. minor show genetic structuring corresponding to known phylogeographic barriers illustrating the dynamic roles regional landscape features played in shaping contemporary S. minor.