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Abstract Detail

Systematics Section

Little, Stefan A. [1], Green, Walton [2], Hickey, L. J. [3], Wilf, Peter [1].

Leaf rank in angiosperms: phylogenetic and ecological variation in leaf vein organization.

Angiosperm phylogeny provides a framework for numerous studies of character evolution. However, vegetative traits comprise only a fraction of evolutionary investigations. This stems, in part, from a historical bias towards reproductive traits, but also from the complexity and variation of many vegetative traits, especially those of leaf venation. A single discrete, semiquantitative trait, leaf rank, provides a useful and rapid summary of overall venation complexity and organization in modern and fossil leaves. Leaves with simple venation are classified as low rank, while leaves with well-organized venation are given high values. Leaf rank has been invoked in several hypotheses regarding angiosperm evolution. These include (1) a shift from low-rank leaves in early angiosperms towards high-rank venation in derived lineages; (2) leaf rank is correlated with environmental conditions, including reductions in rank under dry conditions compared to close relatives under mesic conditions; and (3) the hypothesized trend of increasing leaf rank where leaf structural support is selected. Shifts in leaf-rank in early and recent angiosperm evolution are also (4) considered to be correlated with changes in plant habit. In light of the current DNA-based angiosperm-wide phylogeny, re-testing of these hypotheses is warranted. Here, we investigate the patterns of leaf-rank across the phylogeny of angiosperms, scored for over 1800 genera in 284 families (monocots excluded). All data were scored by one individual (L. Hickey), thus reducing scoring variance. Using recently developed phylogenetic methods, we evaluate the competing hypotheses regarding leaf rank, with implications for untangling some of the interacting factors that influence vein organization through evolutionary history.

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1 - Pennsylvania State University, Department of Geosciences, University Park, PA, 16802, USA
2 - National Museum of Natural History, Smithsonian Institution, Department of Paleobiology, Mrc 121, Washington D.C., 20560, USA
3 - Yale University, Department of Geology & Geophysics, Yale Station, P.O. Box 208109, New Haven, Connecticut, 06520-8109, USA

leaf rank
phylogenetic signal
leaf venation
Leaf evolution.

Presentation Type: Oral Paper:Papers for BSA Sections
Session: 67
Location: Wasatch B/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 2:45 PM
Number: 67008
Abstract ID:880