Background/Question/Methods
Aristida stricta Michx. (Poaceae) is a perennial bunchgrass native to North America where it occurs as the dominant groundcover in longleaf pine savannas and slash pine flatwoods from southeastern North Carolina to Florida, and westward to the coast of Mississippi. Its native habitat has been greatly reduced; consequently, natural populations of A. stricta are also threatened. For conservation and restoration of a species, assessment of its genetic structure is one of the critical needs. We report among- and within- population genetic diversity of A. stricta by using Inter-Simple Sequence Repeat (ISSR) markers. Ten populations were sampled from xeric or mesic sites in North Carolina, South Carolina, Alabama, Georgia, Mississippi, and Florida. Band frequency data for 32 individuals from each of the sampled populations were generated by using eight ISSR primers. Poa pratensis (Family: Poaceae) and Juncus effusus (Family: Juncaceae) were used as out-group taxa. Total number of loci, number of unique loci, percentage polymorphic loci, average heterozygosity, and Nei’s genetic distances were calculated from the two-state data. Analysis of molecular variance (AMOVA) and Mantel tests were conducted to reveal genetic structure, and to estimate the correlation between geographic and genetic distances. A majority rule consensus neighbor-joining tree was generated to establish phylogenetic relationships among the populations.

Results/Conclusions
Average number of loci amplified per population was 101, and almost all (100) had a frequency ≥5%. An AMOVA showed that 38% of the variation resided among populations while 62% was attributable to variation within populations (F_ST = 0.377; P = 0.000). Grouping the populations by habitat (F_CT = 0.006; P = 0.285) or by geographic location (F_CT = 0.007; P = 0.219) did not show significant differentiation between the groups. Overall, pair-wise geographic and genetic distances were not correlated.  Data indicate that while individuals within each population are genetically diverse, there seemingly are barriers to gene flow across populations leading to their divergence.  Each population contains at least some exclusive loci suggesting that different selection pressures may be resulting in this pattern of localization.  Our results, combined with those of the previous studies that presented evidence for local adaptation and phenotypic differences among populations, suggest that there is sufficient variation among populations of this species to warrant: (1) maintenance of the existing genetic diversity at individual sites, and (2) use of local seed and plant sources for conservation projects.