Floral Ontogeny of Mimosoid Legumes.

Abstract

Comparative floral ontogeny in mimosoid legumes was analyzed among representative genera in three major tribes Mimoseae, Acacieae and Ingeae. Details on floral and inflorescence ontogeny in one mimosoid species is described and illustrated for Mimosa strigillosa Torr. & Gray. Three features studied developmentally include: variation in number of parts, patterns of arrangement and inflorescence architecture. Suppression occurs along inflorescences that develop synchronously, when basal flowers are retarded. Tetramerous flowers are considered a reduction or suppression from basic pentamerous flower. Divergent patterns in order of sepal initiation and stamen initiation and proliferation are found during early ontogeny. Four patterns found in the calyx are: helical, simultaneous whorl, bidirectional and ring meristem. Helical is considered primitive and the others derived. Three main types of androecium (haplostemony, diplostemony, multistaminy) were studied developmentally. Four different mechanisms were recognized in the multistaminate androecium: acropetal, lateral, sectorial and helical. Differing patterns in both sepal initiation and stamen initiation occur at non-terminal points in ontogeny. These differences are not reflected in adult morphology due to equalization of size of parts. Since some characters detected during floral ontogeny occur in more than one tribal line it is suspected that parallelisms play a major role in mimosoid evolution.