Variation in the Eucalyptus gunnii-archeri complex. I. Variation in the adult phenotype

A study of variation in the E. gunnii-archeri complex indicates continuous variation between the taxa E. gunnii Hook.f. and E. archeri Maiden & Blakely. Populations assigned to either taxon are normally allopatric but intergrade in an area of parapatry in central Tasmania. The E. gunnii-archeri complex is shown to comprise a multidimensional, clinally varying series of highly differentiated populations. In part, population differentiation appears to result from the interaction of multicharacter clines which parallel several major habitat gradients. This variation is summarized by classification of populations into five main phenetic groups. Whilst considerable differentiation occurs between disjunct stands, a large portion of the variation in the complex occurs in the more or less continuous central stands. In this area, major independent clines are associated with increasing exposure to the alpine environment and the north-south transition between subspp. gunnii and archeri. A peak in variability in geographically intermediate populations is apparent along the latter, but not the former, cline. In addition, it is shown that parallel clines in flowering time have the potential to retard gene flow along these clines. It is suggested that parallel clines which incidentally influence gene flow may be of considerable significance in parapatric differentiation and the origin of reproductive isolation.