Partitioning the genetic diversity within and among populations of Sabatia (Gentianaceae)

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Sabatia is a genus of herbaceous plants residing in the continental eastern North America and the West Indies. One section (Campestria) is found chiefly in Texas, Mexico and the Great Plains region. This section has been treated taxonomically and biosystematically but little is known concerning population structure. This study investigates genetic and morphological subdivision within and among populations of three species of Sabatia; genetic and morphological subdivision in an introgressed population of Sabatia spp.; and genetic differentiation within a population of Sabatia formosa. Natural populations of Sabatia formosa, S. Campestris and S. arenicola were studied throughout the range of the species in Texas. Genetic subdivision within and among populations was determined by using starch gel electrophoresis for 14-15 enzymatic loci for each of the three species. The polymorphic loci for each species were analyzed by using Nei1S genetic statistics. Morphological separation of populations of each species was determined by using a stepwise discriminant analysis of 12 morphological characters. Within and among population morphological variation was determined by using the Mahalanobis D-square distance of every individual from its own population mean and the means of the other populations. For the within population spatial study, spatial autocorrelation was used to determine the nonrandomness of the distribution of alleles. [...]