Implications of leaf and shoot physiology in Podocarpaceae

Abstract

The morphology of many genera in the Podocarpaceae has converged towards compression and reorientation of short shoots to form bilaterally compressed photosynthetic surfaces analogous to broad leaves in angiosperms. A correlation between the degree of shoot flattening and the light intensity required to saturate photosynthetic electron transport was found to exist in a group of podocarps of varying shoot morphology. This suggests that shoot flattening is a strategy associated with growth at reduced light intensity. In contrast to the great variability found in leaf morphology and leaf photochemistry of podocarps, other characters such as xylem tolerance to water-stress induced cavitation are apparently quite inflexible. The range of xylem tolerances in podocarps is low compared to the Cupressaceae, and may explain the restriction of Podocarpaceae to moist environments.