The genetics of Ptychosperma bleeseri, a rare palm from the Northern Territory, Australia

Ptychosperma bleeseri is known from only eight small monsoon rainforest patches located in the vicinity of Darwin, Australia. One population consists of only one adult plant and only one patch contains a population of more than 50 adult plants. A survey of the genetic diversity within the species was undertaken using isozyme analysis. Almost no genetic variation was recorded. Of the 223 wild collected samples tested, only four individuals varied at a single locus out of the 10 loci analyzed. The lack of diversity among populations suggests that the existing populations are derived from a common, genetically depauperate, source which has acted as a founder population. P. bleeseri was compared with the other Ptychosperma species which occur naturally in Australia (P. macarthurii and P. elegans). Each of these species was found to differ consistently at several enzyme loci thus indicating that P. bleeseri does not simply represent an outlying population of either of these two species. Cultivated specimens of P. bleeseri were shown to have hybridized with other cultivated Ptychosperma species when grown together. This presents a problem for ex-situ conservation. Since palms are particularly favoured by Darwin residents in their gardens and public places, the location of urban development in close proximity to wild populations of P. bleeseri has the potential to introduce other Ptychosperma species into the wild populations. This could have serious effects on the genetic integrity of the species.