Calcium oxalate crystals are common in leaves and other tissues throughout the angiosperms. The morphology and distribution of crystals vary widely among genera and often between closely related species. These traits have been shown to be systematically relevant in some cases. Phylogenetic relationships among members of the cotton genus and tribe are reasonably well understood, providing a context for evaluating evolution of leaf crystal patterns in the group. An anatomical study was undertaken, using leaf clearings, to characterize the type, morphology and patterns of the crystals. Patterns of crystal distribution and morphology are compared among taxa and are evaluated with respect to phylogeny and biogeography.

Key words: calcium oxalate crystals, cotton, Gossypium, leaf anatomy