Genetic Divergence of Chamaecrista fasciculata (Fabaceae) Variants and Conservation Implications for the Rare Tidal Marsh Form.

Premise of research. Chamaecrista fasciculata is a widespread species harboring intraspecific morphological and ecological variability. Taxonomists have previously recognized intraspecific variants of C. fasciculata at specific, varietal, and ecotypic levels, but studies have not tested the hypothesis that these variants are genetically differentiated. In this study, we quantified genetic variation in populations of C. fasciculata to assess genetic differentiation and structure of the tidal freshwater endemic form, var. macrosperma , from the more common upland form, var. fasciculata. Methodology. Population genetic variation was quantified by genotyping 240 plants across 11 populations (8 var. fasciculata and 3 var. macrosperma) with 15 microsatellite loci. We compared genetic variation between the varieties, tested for geographic structure and historical bottlenecks in each population, and identified potential intervarietal hybrids. Pivotal results. Lower allelic diversity and heterozygosity were found in var. macrosperma , but these populations harbored more private alleles than var. fasciculata. Analysis of molecular variance indicated that 6% of the variation resides between the varieties, and Bayesian assignment analysis supported two genetic clusters, which align with morphological distinction of the varieties. Despite occurring in distinct habitats, admixture was found in all populations. Genetic bottlenecks were detected in some populations, which may reflect founder events from small numbers of seeds and the ephemeral nature of populations of this annual species. Conclusions. Given the significant genetic differentiation observed between the varieties, we recommend the continued taxonomic distinction of these varieties. The infrequent occurrence of var. macrosperma in tidal freshwater wetlands in combination with the strong genetic differentiation among populations we identified here is a conservation concern for this taxon. To preserve genetic diversity of var. macrosperma , efforts should focus on maintaining all extant populations and preserving suitable habitat to allow for colonization of new populations. [ABSTRACT FROM AUTHOR]