Population genetic structuring in a rare tropical plant: Idiospermum australiense (Diels) S.T. Blake

Idiospermum australiense (Diels) S.T. Blake is considered to be one of the few remaining species of an ancient assemblage to have survived the attrition of Australian tropical rain forest during historically drier periods. This monotypic species is currently restricted to two very wet lowland rain forest locations in Australia’s wet tropical World Heritage Area that are thought to have provided refuge for humid-adapted taxa during the last glacial maximum. Two dominant (RAPD and ISSR) molecular marker sets were employed to investigate whether the genetic structure of Idiospermum could be attributed to its restriction to these quite disjunct localities. The results reveal that neither its restriction to purported Pleistocene refugia nor the geographic distance between populations could fully explain the distribution of variation in the Idiospermum data set, with evidence to suggest that potentially deeper time events have played a role in population structuring and the distribution of diversity. Although there is sufficient evidence in the data to suggest that gene dispersal is quite limited in the species, further investigation is still needed to yield more informative detail on additional factors, such as breeding and germination strategies and their potential influence over population structuring and diversity levels within each population and refugium.