A preliminary study of allozyme variation in three rare and restricted endemic Barleria greenii (Acanthaceae) populations

Barleria greenii is a rare endemic taxon with an extremely restricted distribution area found only near Estcourt, South Africa. Three of eight known populations of B. greenii, representing a hierarchy from closely spaced to geographically distant sites, were studied by horizontal starch gel electrophoresis to assess the levels of genetic variation and to estimate the amount of genetic differentiation. among populations. Sixteen enzyme coding loci provided interpretable results in all populations analysed, of which seven (43.8%) displayed polymorphism and nine (56.2%) displayed monoallelic gel banding patterns. Staining of some enzymes, which provided interpretable results in previous studies of other Barleria species, did not give any results in this study. The levels of genetic diversity measured in B. greenii are somewhat higher than the means for endemic populations, except for Population 1 and the average heterozygosity of Population 2a. Values of the mean number,of alleles per loci increased progressively from the east (Population 1) to the west (Population 3)indicating clinal distribution. Short seed dispersal distance, parasitism and isolation by distance:are considered to be the most likely explanations for the low genetic divergence encountered in the studied populations. The low genetic variability in B. greenii may also be a result of frequent or infrequent local extinction, possibly due to fires; therefore, fire regime should favour establishment of seedlings and resprouting of B. greenii. (C) 2002 Elsevier Science Ltd. All rights reserved.