Leaf morphological and anatomical characteristics of heteroblastic Eucalyptus globulus ssp globulus (Myrtaceae)

Leaf characteristics of Eucalyptus globulus Labill. ssp. globulus vary in r esponse to plant genotype, ontogenetic position and environmental condition s. Glasshouse-grown seedlings from provenances at St Marys, Tasmania, and W ilsons Promontory, Victoria, produced seedling leaves for 10 nodes before p roducing leaves of juvenile form. Tasmanian provenance seedlings began to p roduce juvenile leaves after 18 weeks, 4 weeks earlier than Wilsons Promont ory seedlings. Tasmanian seedlings continued to produce juvenile foliage, w hereas Wilsons Promontory seedlings began producing transitional leaves at 33 weeks. Successive transitional leaves ranged from the juvenile to the ad ult leaf form owing to variability in the rate of change of particular morp hological and anatomical leaf characteristics. Retention of broad, thin, se ssile, horizontally oriented, dorsiventral, hypostomatal juvenile leaves of Tasmanian seedlings assists in increasing growth rates under mesic conditi ons. Early production of thick, narrow, petiolate, vertically oriented, iso bilateral, amphistomatal adult leaves by Wilsons Promontory seedlings appea rs to be related to the stressful conditions within its local habitat. An i ncrease in amphistomy and the distribution of palisade mesophyll on both le af surfaces with ontogenetic development was strongly related to leaf orien tation and light interception, increasing the supply of CO2 for photosynthe sis.