PHENOTYPIC, GENETIC AND ECOLOGICAL VARIATION IN THE EUCALYPTUS-SALIGNA-E-BOTRYOIDES COMPLEX

Analysis of variation within the E. saligna-E. botryoides complex indi cates a continuum of morphological variation, particularly in bud, fru it and bark characters, between the taxa. The continuum occurs between populations north of Sydney (which had always been recognised as E. s aligna), and populations restricted to the coastal fringe (which had a lways been recognised as E. botryoides). There is a suggestion of a la titudinal cline in morphology of the intermediate populations, althoug h it is complex, and shows significant local variation. Analysis of al lozyme data indicates that most of the genetic variation within the co mplex is contained within rather than between populations, and that ge netic distances between populations are more typical of within-species rather than between-species differences. The lack of allozyme diverge nce is attributed to either relatively rapid and recent differentiatio n or to extensive introgression following secondary contact of the tax a. Analysis of environmental variables reveals two discriminating fact ors in relation to the current distributions of populations within the complex. Firstly, the morphological gradient appears to follow an und erlying temperature gradient, and secondly, E. botryoides occupies a s eparate niche associated with the distinct coastal environment on whic h it occurs. These key environmental parameters may have been importan t in the evolution of the complex along axes of latitude or temperatur e, and coastal versus inland habitat. Additionally, changes in distrib ution of the taxa as a result of climatic changes associated with glac ial-interglacial cycles may also have played an important role in the formation of the complex.