9420158 Tucker Recent molecular analyses of DNA variation in putatively primitive members of the legume family Leguminosae (Fabaceae) as well as continued morphological studies have emphasized our poor understanding of the taxonomic relationships among the genera of the subfamily Caesalpinioideae. These are typically woody plants of tropical regions of the world, some of which are nitrogen- fixers and hence important ecologically as well. Dr. Shirley Tucker of Louisiana State University is studying the early ontogenetic or developmental stages of floral form in a broad sample of genera of caesalpinioid legumes, using light and scanning electron microscopy. The goal is to characterize the sequential stages of sepal, petal, stamen, and ovary initiation, relative positioning, fusion of parts if any, and maturation, leading to the final structure of the flower in this group of plants. Specialized floral shape and size often result from seemingly minor shifts in the timing and positioning of developing floral organs. Evidence about these morphological shifts in pattern formation is useful for assessing the taxonomic and phylogenetic relationships among plant groups. Detailed morphological studies of floral form and ontogeny provide criteria for assessing the homology of taxonomic characters used to infer phylogenetic relationships. Dr. Tucker's morphological findings will be integrated with new molecular data from DNA analyses to improve understanding of the early evolution of the legume family.
