Unusually high genetic variability revealed through allozymic polymorphism of an endemic and endangered Australian orchid, Pterostylis aff. picta (Orchidaceae)

Sixteen enzyme loci were used to assess levels of genetic diversity within populations of Pterostylis aff. picta, and the degree of genetic divergence among them. We found a high level of genetic diversity both at population and species level. The percentage of polymorphic loci (P), the number of alleles per locus (A), observed and expected heterozygosity (H o, H e) were 69.47%, 2.04, 0.275 and 0.284, respectively. The G st value among the nine populations examined was 0.05 suggesting that around 95% of variation resides within populations. The average gene flow (N m) value of 4.37 indicates that gene flow is sufficient to impede genetic structuring. Despite the narrowness of distribution and a recent rapid decline in population size due to various ecological factors, high genetic variability and low population divergence were found to be present. Higher genetic variability may also be due to extensive gene flow maintained by seed and pollen movement. Although endemic and restricted in distribution, P. aff. picta harbours higher levels of genetic variation than other orchids with larger populations and is unlikely to be endangered by genetic factors.