The Functional Significance of Leaf Shape Variation - Towards a Consensus from Gene to Community
Boyce, C. Kevin .
Intrinsic factors shaping the evolution of leaf morphology over geologic time.
Over the history of vascular plants, three important transitions in leaf morphology--the initial evolution of laminate leaves, the progressive loss of seed plant morphological diversity, and the evolution of more angiosperm-like leaves--correspond to major shifts in leaf functional roles or development. These transitions often occurred in parallel in different lineages, each time with similar morphological consequences. First, laminate leaves evolved independently in ferns, seed plants, and two exclusively Paleozoic lineages during the Devonian and Carboniferous. This process involved the convergent evolution of marginal laminar growth in each lineage as inferred from details of lamina venation of fossils and confirmed with developmental study of living taxa. Second, seed plants shared with the ferns the full range of morphologies associated with marginal laminar growth during the Paleozoic, but lost most of this morphological diversity over the Mesozoic (recognized in the literature as part of the Paleophytic/Mesophytic transition). This loss of morphological diversity is closely associated with a change in seed plant reproductive biology: like ferns, early seed plants tended to bear reproductive structures directly on foliage leaves and it is specifically the lineages that segregate reproductive and vegetative functions that exhibit a loss of leaf morphologies. Third, complex angiosperm-like characteristics of leaf venation have evolved independently in several seed plant lineages, beginning with the Permian Gigantopterids, and a number of distinct fern lineages, beginning in the Triassic with the Dipterids. Presumably, the many independent evolutions of angiosperm-like leaves each involved departures from marginal growth similar to those of the angiosperms, although that hypothesis has not been tested. Each of these evolutionary transitions in leaf morphology also represents a dramatic reorganization of the venation and hydraulic architecture.
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1 - University of Chicago, Department of Geophysical Sciences, 5734 S. Ellis Avenue, Chicago, Illinois, 60637, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Williford B/Hilton
Date: Monday, July 9th, 2007
Time: 10:45 AM