Genetic and morphological analysis of multi-stemmed plants of tuart (Eucalyptus gomphocephala)

Abstract

The tuart–banksia woodlands of the Swan Coastal Plain in Western Australia are characteristic vegetation communities of this coastal region, and Eucalyptus gomphocephala DC. (Myrtaceae; tuart) is an iconic tree of these communities. The species primarily occurs as a tall single-stemmed tree, but at the northern end of the distribution, it also occurs in a multi-stemmed form. Growth habit is frequently used as a taxonomic character in eucalypts, with many complexes having tree and mallee forms, although the genetic characterisation of growth habit in eucalypts has been limited. We investigated the genetic and morphological differentiation among populations of tree and multi-stemmed forms of tuart at the northern end of its distribution. Although the populations showed moderate levels of genetic diversity on the basis of microsatellite markers, as might be expected from populations on the periphery of the distribution, there was no evidence of genetic differentiation associated with the tree and multi-stemmed forms. Morphometric analysis showed some differences in the size of buds and fruits among the populations. Our analysis is consistent with environmentally induced variation in tuart in near-coastal populations where plants grow on poor soils and form may be affected by wind and salt exposure. This result adds to other evidence from pines and Nothofagus of environmental rather than genetic influences on growth form, particularly in stressful environments.