A paedomorphocline in Eucalyptus: natural variation in the E. risdonii / E. tenuiramis complex

Ontogenetic and morphological variation in 40 natural populations of the closely related species, <i>E. risdonii</i> and <i>E. tenuiramis</i>, were assessed in a multivariate study of juvenile and adult leaf and fruit characters. The present taxonomic separation of the two taxa is based mainly on ontogenetic differences, but this study reveals that the variation between the two taxa in the retention of the juvenile leaf habit is continuous and may represent a paedomorphocline. The morphological data suggest that at least four phenetic groups are required to summarise the morphological variation in the <i>E. risdonii / E. tenuiramis</i> complex. When ontogenetic variation is removed, the morphological variation between some <i>E. risdonii</i> and some <i>E. tenuiramis</i> populations is also continuous and much smaller than the morphological differences within <i>E. tenuiramis</i>. This suggests that <i>E. risdonii</i> may be the product of relatively recent changes in developmental timing (heterochrony) from <i>E. tenuiramis</i>.