Leaf Heteroblasty in Pseudopanax crassifolius: Functional Significance of Leaf Morphology and Anatomy

Abstract

Pseudopanax crassifolius (A. Cunn.) C. Koch. is a strongly heteroblastic tree indigenous to New Zealand. Changes in the morphology and anatomy of leaves are described for seedling, juvenile, transitional and adult phases of development. Seedlings produce five leaf types; all are relatively small, thin, anthocyanic, have a low specific weight, and are anatomically comparable to the leaves of many shade plants. Juvenile leaves are long, linear, deflexed, coriaceous and sharply-toothed. They have a high specific weight, a thick, ornamented cuticle, a multiseriate hypodermis composed of collenchyma, well developed palisade and many spongy mesophyll layers. Juvenile leaves are strong relative to adult leaves and to the leaves of other species. Leaf strength is provided by fibres associated with the midrib. Adult leaves are shorter, broader and less massive than juvenile leaves, and are oriented horizontally. Transitional leaves are morphologically intermediate between juvenile and adult leaves. The anatomy of juvenile, transitional and adult leaves is similar. The heteroblastic series may be associated with changes in leaf construction costs, light interception and heat dissipation.