COMPARATIVE FLORAL DEVELOPMENT IN CLEOMACEAE REVEALS TWO DISTINCT PATHWAYS LEADING TO MONOSYMMETRY

Comparisons of floral symmetry have important implications for understanding ecological, evolutionary, and molecular mechanisms driving the diversification of angiosperms. Examination of symmetry in Cleomaceae provides an opportunity to compare monosymmetric flowers with the polysymmetric (disymmetric) flowers generated by its sister family, Brassicaceae. In order to better understand the origins of monosymmetry, we studied floral development in 11 species of Cleomaceae. Although all flowers were monosymmetric due to upward curvature of the petal bases near anthesis, two distinct patterns of early development were identified: early monosymmetry and early disymmetry. An enlarged abaxial sepal relative to the other three and petals that remain small in the bud characterize species exhibiting early monosymmetry, while four equally sized sepals throughout development and petals that grow rapidly are found in species with early disymmetry. When these pathways were compared to a phylogeny of the family, a single, derived origin of the disymmetric pathway was observed. Although these interpretations are based on limited sampling and lability exists in early development, we hypothesize that the early monosymmetric developmental pathway is shared with Brassicaceae. These studies also indicate that early and late development are disassociated in Cleomaceae and reveal that dynamic developmental patterns underlie seemingly similar mature morphologies.