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(American Journal of Botany. 2005;92:1616-1623.)
© 2005 Botanical Society of America, Inc.

Anatomy and Morphology

Correlated evolution of leaf shape and trichomes in Begonia dregei (Begoniaceae)1

Tracy McLellan2

School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg, Private Bag 3, WITS 2050, South Africa

ABSTRACT

Structural features of leaves, including size, shape, and surfaces, vary greatly throughout the plant kingdom. In both functional and phylogenetic analyses of leaves, the various morphological aspects are often considered independently of each other, although it is likely that many combinations of features do not occur at random due to either functional constraint or genetic correlation. The distribution of variation in leaf morphology in the highly variable Begonia dregei species complex was examined in natural populations and in F2 offspring from a cross between plants from two populations. Leaf shape was quantified using several morphometric measures, and trichomes on leaves were counted and measured. Correlations between leaf shape and the numbers and size of trichomes were examined. There were significant correlations between the shapes of leaves and the presence, number, and size of trichomes among populations and in hybrid plants. Deeply incised leaves had larger numbers of longer trichomes at the sinuses. Higher numbers of trichomes on upper leaf surfaces occurred together with trichomes at the petiole and on the abaxial surface. The potential for independent evolution of leaf shape and trichomes in this group is limited. Hypotheses to explain the correlated development of leaf shape and trichomes are discussed.

Key Words: correlated evolution • developmental constraint • genetic correlation • leaf incision • leaf shape • morphological evolution






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