Phylogenetic Implications of Inflorescence and Floral Ontogeny of Mimosa Strigillosa

Ontogeny of the inflorescence and flower of Mimosa strigillosa has been studied in order to explore the developmental basis for variation in number of parts, patterns of organ arrangement, and inflorescence architecture. Each racemose inflorescence of M. strigillosa has an acropetal order of initiation of bracts and flowers. Although flowers are initiated in acropetal order, they develop synchronously except for the basal flowers, which are retarded. The ring meristem in the calyx may be considered an expression of precocious fusion, a specialized condition within the genus. Two patterns of organ arrangement (nonsagittal and median sagittal) are distributed among 4‐ and 5‐merous flowers along the inflorescences. Variability in number of parts probably has evolved through reduction of a basic, pentamerous structure, through fusion or suppression. It is proposed that the number of parts and pattern of organ arrangement are correlated features.