A common boundary between distinct northern and southern morphotypes in two unrelated Tasmanian rainforest species

Abstract

The variation in selected leaf morphological traits was examined across the geographic ranges of two Tasmanian rainforest species, Tasmannia lanceolata (Poiret) A.C.Smith and Eucryphia milliganii Hook.f. Comparisons of field- and glasshouse-grown plants for both species showed that there is strong genetic control of all the morphological characters measured. Two distinct morphotypes, occupying similar areas of Tasmania, were identified in each species. The geographic boundary between the morphotypes is similar in both species and runs more or less east–west, separating each species into northern and southern forms. Southern E. milliganii differs from the northern form in having ovate leaves with dense marginal trichomes and a pubescent abaxial leaf lamina. A new subspecies, E. milliganii ssp. pubescens, is described to encompass this intra-specific variation in southern Tasmania. Southern T. lanceolata has encrypted stomata, contrasting with the superficial stomata of the northern form, but is not considered sufficiently different to warrant separate taxonomic status. The boundary is difficult to explain in terms of modern environmental factors. A past period of significantly different climate from the present, perhaps combined with anthropogenic fire regimes, may have enabled allopatric differentiation within each species.