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

Leaf characteristics of Eucalyptus globulus Labill. ssp. globulus vary in response to plant genotype, ontogenetic position and environmental conditions. Glasshouse-grown seedlings from provenances at St Marys, Tasmania, and Wilsons Promontory, Victoria, produced seedling leaves for 10 nodes before producing leaves of juvenile form. Tasmanian provenance seedlings began to produce juvenile leaves after 18 weeks, 4 weeks earlier than Wilsons Promontory seedlings. Tasmanian seedlings continued to produce juvenile foliage, whereas Wilsons Promontory seedlings began producing transitional leaves at 33 weeks. Successive transitional leaves ranged from the juvenile to the adult leaf form owing to variability in the rate of change of particular morphological and anatomical leaf characteristics. Retention of broad, thin, sessile, horizontally oriented, dorsiventral, hypostomatal juvenile leaves of Tasmanian seedlings assists in increasing growth rates under mesic conditions. Early production of thick, narrow, petiolate, vertically oriented, isobilateral, amphistomatal adult leaves by Wilsons Promontory seedlings appears to be related to the stressful conditions within its local habitat. An increase in amphistomy and the distribution of palisade mesophyll on both leaf surfaces with ontogenetic development was strongly related to leaf orientation and light interception, increasing the supply of CO2 for photosynthesis.