Observations of high genetic variability in the endangered Australian terrestrial orchid Pterostylis gibbosa R. Br. (Orchidaceae)

The genetic variation in all known populations of an endangered Australian native terrestrial orchid Pterostylis gibbosa R.Br., was investigated with starch gel electrophoresis. A total of 16 isozyme loci were assayed. The pe rcentage of polymorphic loci (P), the number of alleles per locus (A), obse rved and expected heterozygosity at population levels were 69%, 2.21, 0.210 , 0.261, respectively. The G(st) value of 15% indicates that around 85% of variation resides within populations. Despite isolation by distance most al leles were distributed across most of the populations. High genetic variabi lity along with low population divergence may be the result of recent popul ation fragmentation or from extensive gene flow maintained by seed and poll en movement. To investigate whether poor seed viability contributed towards its rarity, an orchid seed viability test using Fluorescein diacetate reve aled high seed viability (range 68-90%). Although endangered and restricted to only four geographical areas, P. gibbosa showed a higher level of genet ic variation than other orchids with larger populations. (C) 2000 Elsevier Science Ltd. All rights reserved.