Cladistic and Phenetic Analyses of Phylogenetic Relationships Among Populations of Eucalyptus caesia

Abstract

Numerical cladistic and phenetic analyses were undertaken on allozyme and morphometric data from 11 populations of the south-western Australian granite rock mallee Eucalyptus caesia. Differing minimum-length Wagner networks were obtained from both the continuous and binary coded allozyme and morphometric data sets. Pooling the continuous allozyme and morphometric data sets, or analysing the morphometric data set alone, gave the most biogeographically parsimonious networks. These analyses suggest that, of the two subspecies of E. caesia, magna is monophyletic while caesia is paraphyletic. Magna probably was derived from an ancestral population of caesia to which the extant Yanneymooning Hill caesia population shares the closest phylogenetic relationship. The most western caesia population bears the closest affinity to the putative ancestor of the species as a whole, and a sequence of increasingly derived caesia populations occurs eastwards, as does the derived subspecies magna.

In most cases, equally plausible and largely congruent phylogenetic reconstructions were obtained using either cladistic or phenetic analyses of the same data sets in E. caesia. The possible occurrence of interpopulational hybridization between neighbouring populations and of differential rates of allozyme and morphometric character state changes may have introduced errors in the phylogenetic reconstructions obtained by cladistic and phenetic methods.