Genetic variation within and among populations of Ligularia virgaurea (Asteraceae), an invasive weed in the grassland ecosystem of the QinghaiTibetan Plateau

The genetic mechanism and subsequent control of exotic invasive species have received extensive attention within recent years, but little attention has been paid to native weeds restricted to local ecosystems. Ligularia virgaurea is a clonal species of Asteraceae and reproduces asexually by underground rhizomes and sexually by seeds, which distributes throughout alpine meadows of the QinghaiTibetan Plateau. In the present study, random amplified polymorphic DNA (RAPD) markers were used to evaluate genetic variation and clonal diversity of 11 populations of Ligularia virgaurea. A total of 81 amplified bands were scored from the 13 RAPD primers, giving a mean of 6.23 amplified bands per primer, and 74.07% (61 bands) were found to be polymorphic bands (PPB), indicating a remarkable level of genetic variation at the species levels. The percentage of polymorphic loci within population ranged from 19.45% to 60.49%, and the mean Nei gene diversity (He) was 0.169 8, indicating a moderate variation in the genetic diversity of L. virgarea. RAPD phenotypes (genotypes) among populations were highly rich and variable. Moreover, an analysis of molecular variance (AMOVA) showed that 67.64% of the total genetic variation was found among individuals within population, while 31.74% was between populations. Contrary to the initial assumption that this clonal weed has a low diversity and population differentiation, results suggested that both the genetic diversity and amongpopulation differentiation of L. virgarea are high comparing to the average of the other nonclonal or noninvasive species. We proposed that the sexual recruitment and longdistance colonization characteristics, perhaps in combination with genetic introgression, are responsible for such a pattern of genetic structure in this local weed.