Variation in seedling morphology in the Eucalyptus risdonii-E. tenuiramis complex

The genetic differentiation of populations within the E. risdonii Hook.f.-E. tenuiramis Miq. complex and the affinities of isolated peppermint populations from Tasmania's south-west World Heritage Area (WHA) were assessed in a morphometric study of glasshouse-grown seedlings. Four well-differentiated phenetic groups within the E. risdonii-E. tenuiramis complex were identified: (1) E. risdonii, (2) Southern E. tenuiramis, (3) Northern E. tenuiramis and (4) Peninsula E. tenuiramis. The differentiation between populations identified as E. risdonii and Southern E. tenuiramis is much smaller than the separation between the extreme forms of E. tenuiramis (Northern and Peninsula E. tenuiramis). The differentiation in the E. tenuiramis complex is associated with geography and substrate type, with the Southern morph restricted to sedimentary substrates and the other morphs to igneous substrates. The WHA populations have a juvenile morphology intermediate between E. coccifera and Peninsula E. tenuiramis, with closest affinities to E. tenuiramis and other E. coccifera-E. tenuiramis intermediates. The current taxonomic treatment of E. risdonii and E. tenuiramis as separate species is not consistent with the patterns of genetic differentiation within this complex and their presumed phylogenetic relationship. The populations from the WHA represent a taxonomic entity that is restricted to this area. The evolutionary processes that may have shaped the patterns of variation within the E. risdonii-E. tenuiramis complex are discussed.