Geographic variation and plasticity of leaf shape and size in Begonia dregei and B. homonyma (Begoniaceae)

The distinction between Begonia dregei and B. homonyma has hitherto been based on differences in the shape and size of leaves. A large sample of field-collected leaves has been examined using quantitative methods to test the validity of this distinction. Comparisons of leaf shape, with and without the inclusion of size-related variables, revealed three groups with a small amount of overlap, two of which correspond to B. dregei and one to B. homonyma. Effects of environmental conditions on leaf shape and size were examined in plants from four populations grown at two light intensities and compared with field collections. Leaf size varied little with environment, while margin roughness varied with the different conditions and there was variation among populations in the magnitude and direction of responses. These results show that leaf shape and size can be used as valid discriminators of groups within this taxon. Resolution of the taxonomy of this group will require consideration of heterogeneity within each of the three groups based on leaf shape and size. (C) 2000 The Linnean Society of London.