Sporck, Margaret J , Sack, Lawren .
Exceptional diversification of leaf surfaces in the Hawaiian Chamaesyce.
The Hawaiian Chamaesyce (Euphorbiaceae) are a group of C4 dicots that radiated from one colonizing species into nearly 30 taxa. This group is present on all of the main islands and includes a variety of life forms, from creeping woody sub-shrubs to trees over 6 m tall, with taxa adapted to diverse habitats, from rain forest to dry forest to coastal vegetation. The leaves of the Hawaiian Chamaesyce taxa vary strongly, but no study so far has examined stomatal traits. Typically plant species have stomata distributed only on the abaxial (lower) surface of the leaf (hypostomaty), or on both the abaxial and adaxial (upper) surfaces (amphistomaty). The distribution of stomata only on the adaxial surface (hyperstomaty) is rare, previously documented in various aquatic plants, grasses, and some high elevation herbs that fold their leaves to prevent water loss, but not in typical terrestrial dicots. For 29 Chamaesyce taxa we determined stomatal characteristics using scanning electron microscopy of leaf surfaces, light microscopy of epidermal peels, and porometry. For each taxon we quantified stomatal numbers, dimensions and distribution; we tested for correlation of these traits with the source population elevation, mean annual rainfall, temperature, and relative humidity, and with leaf size and thickness. We found an unexpectedly large diversity in stomatal density and in stomatal distribution, including hypostomaty, amphistomaty and, for several taxa, hyperstomaty. Apparently, Hawaii’s isolated location and strong climatic gradients have driven stomatal trait diversification for Chamaesyce beyond any previously characterized in a given lineage. We explore possible hypotheses for the evolutionary factors involved, and the functional significance of this diversity.
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1 - University of Hawaii at Manoa, Department of Botany, 3190 Maile Way, Room 101, Honolulu, HI, 96822, USA
2 - University of California, Los Angeles, Ecology and Evolutionary Biology, 621 Charles E. Young Drive, Los Angeles, CA, 90095, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Tuesday, July 29th, 2008
Time: 9:00 AM