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Paleobotanical Section

Lyon, Mandela A. [1], Wing, Scott L. [2].

A quantitative morphospace for dicot leaves.

Dicotyledonous angiosperm leaves exhibit a wide range of morphologies, with variation occurring in multiple components of laminar form. Differences in shape are likely adaptive, as aspects of leaf morphology covary with climate, habitat, habit, and ecology. Traditional systems for describing leaf morphology have been primarily qualititative or semiquantitative, although some studies have examined the relationship between climate and a limited set of quantitative measurements of leaf form. Here we propose a fully quantitative morphospace that provides a reasonably complete description of dicot leaves, allowing local floras to be characterized without the particularities of scoring procedures and the imprecision introduced by different observers. The primary dimensions of dicot leaf morphospace include blade area and perimeter; base and apex angle; whole-blade, base, and apex symmetry; length:width ratio, distance along midrib to maximum blade width; tooth importance; and blade lobation. These dimensions reflect aspects of leaf form typically characterized in qualitative analyses, and results of leaf outline analyses indicate that these dimensions are fundamental features of leaf shape variation. The morphospace has been tested preliminarily against leaves from two modern New World floras (Barro Colorado Island, Panama, and York County, Pennsylvania; 196 species in 69 families). Tropical and temperate floras appear to occupy semi-distinct areas of the morphospace, with centroids distinct both from each other and from the overall centroid, although there is considerable overlap. Overall, the dicot leaf morphospace is large but only sparsely occupied at the edges. Tropical and temperate floras together occupy a limited volume of the total morphospace, despite being moderately distinct from one other. Although this quantitative morphospace currently requires complete (or artificially healed) leaf outlines, it is an effective way of analyzing variation in leaf form. We plan to apply this approach to fossil leaf assemblages to examine change through time in dicot leaf morphospace occupation.


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1 - University of Pennsylvania, Department of Earth & Environmental Science, 240 S. 33rd St., Philadelphia, Pennsylvania, 19104-6316, USA
2 - Smithsonian Institution, National Museum of Natural History, Deptartment of Paleobiology, MRC-121, PO Box 37012, Washington, DC, 20013-7012, USA

Keywords:
leaf
morphology
morphospace
Tropical
temperate
flora
dicot
angiosperms.

Presentation Type: Oral Paper
Session: 32-6
Location: Salon G - Austin Grand Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 11:30 AM
Abstract ID:495


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