Development of Microsatellite Markers to Evaluate Current Species Boundaries between Liatris helleri Porter and Liatris turgida (Gaiser) (Asteraceae)

Clark, Logan

ABSTRACT: Liatris helleri Porter (Asteraceae), Heller’s blazing star, is a rare perennial herb endemic to high elevation rock outcroppings in the Southern Appalachians. This species has a showy spiked inflorescence with purple flowers that is easily noticed during its flowering period of late July through September. There are less than 10 extant populations of L. helleri known throughout western North Carolina, all within a 30 km radius of each other (Godt and Hamrick, 1995). Botanists have historically relied on its short stature, occurrence in high elevation rock outcrop communities, and its short pappus length to distinguish this species from its congener, Liatris turgida Gaiser (Nesom, 2005b). L. turgida, the shale barren blazing star, is a lower elevation species that displays a similar and sometimes overlapping morphology to that of L. helleri. The separation of these two taxa as individual species has been historically contentious with previous studies of genetic diversity and morphology suggesting the possibility that together they might represent a single species with an expanded range. The genus Liatris is composed of approximately 40-50 species located predominately along the eastern seaboard of North America. Broad species ranges in this genus can sometimes lead to polyspecies sympatry where three or more species coexist. This co-occurrence can lead to hybridization between species on rare occasions and a lack of well-defined ecological differentiation (Levin, 1967). Liatris is a genus known to display “unusual difficulty” in specific determination likely due to these occurrences of hybridization and phenotypic plasticity (Gaiser, 1946). Previous genetic studies in this species employed lower resolution markers such as allozymes and cpDNA markers (Godt and Hamrick, 1996; Sullins 2013). Allozyme studies found highly structured populations, with high genetic diversity. The phylogeographic approach used by Sullins (2013) employed cpDNA markers, which provided no clear separation of L. helleri and L. turgida, resulting in incomplete lineage sorting. The current study involves the development of a series of 17 microsatellite markers, which were then employed to investigate the genetic diversity, population structure, and genetic distance between these two taxa. To accomplish this, 21 populations and 327 individuals across the range of L. helleri proposed by Nesom (2005b) were sampled and genotyped using 12 of the microsatellite markers developed for this study. This study identifies a genetically distinct metapopulation of L. helleri, distinct populations of L. turgida, and admixed populations. Population structure within L. turgida was also identified and baseline genetic diversity statistics for both species were calculated. The results from this study in conjunction with previous studies offer a more comprehensive understanding toward our concept of L. helleri and provide genetic data to inform management decisions. Based on the findings generated in this study L. helleri should retain its species distinction separable from L. turgida, at least at a subspecies level.