Leaf gigantism in coastal areas: morphological and physiological variation in four species on the Tasman Peninsula, Tasmania
Christopher J. Blackman A , Gregory J. Jordan A B and Robert J. E. Wiltshire AA School of Plant Science, University of Tasmania, GPO Box 252-55, Hobart, Tas. 7001, Australia.
B Corresponding author. Email: greg.jordan@utas.edu.au
Australian Journal of Botany 53(2) 91-100 https://doi.org/10.1071/BT04040
Submitted: 9 March 2004 Accepted: 29 November 2004 Published: 31 March 2005
Abstract
Leaf gigantism is an example of marked morphological variation associated with abrupt environmental gradients of increasing coastal exposure. This study characterises the morphology and anatomy of leaf gigantism in four species across two habitats on the coastal headlands of the Tasman Peninsula, Tasmania, Australia. In addition, the genetic basis and adaptive significance of leaf gigantism are examined. Leaf gigantism was characterised in Leptospermum scoparium, Acacia verticillata and Allocasuarina monilifera by greater thickness and succulence, and by greater thickness and increased support tissue in Allocasuarina crassa. Glasshouse-grown seedlings of each species derived from exposed and inland field sites showed that leaf gigantism has both genetic and environmental components. Leaf succulence and a slower growth rate were shown to be heritable in seedlings from the exposed site of L. scoparium and A. verticillata, indicating genetic differentiation. In the reciprocal translocation trial, the higher degree of stress tolerance (as measured by chlorophyll florescence) exhibited by seedlings of L. scoparium and A. verticillata from the exposed site demonstrated the adaptive significance of leaf gigantism in these species. The ecological and evolutionary implications of leaf gigantism on the Tasman Peninsula are discussed.
Acknowledgments
We thank the Tasmanian Department of Primary Industry, Water and Environment for permission to collect specimens and perform the translocation experiment within the Tasman National Park. We also thank the Pryor family for permission to establish an experiment on their property.
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