Inflorescence morphology, heterochrony, and phylogeny in the mimosoid tribes Ingeae and Acacieae (Leguminosae : Mimosoideae)

In earlier work (Grimes, 1992) on inflorescence morphology ir. the mimosoid tribes Ingeae and Acacieae I proposed that differences in inflorescence mo rphology result from three properties: the organization of components of th e inflorescence and their relative positions; the hierarchical arrangement of the axes of the inflorescence and the position they assume in total tree architecture; and the heterochronic development of components of the inflo rescence. Further work shows that the first two properties are better state d in terms of heterochrony; namely, that the organization of components of the inflorescence differs due to differences in timing of the development o f organ systems and that the hierarchy of axes likewise differs due to hete rochronic changes. Neither de novo origin of organs or organ systems nor su ppression or loss of organs or organ systems accounts for the diversity in form. Observed heterochronic differences in the inflorescence structure may be divided into three types: spatial differences in the relationship betwe en the unit inflorescence and the subtending leaf(hysteranthy); differences in the time of formation and/or the duration of whole axes; and changes in development pathways, leading to shoot dimorphism. These heterochronies ar e used as characters in a cladistic analysis, and it is shown that although some are homoplasious,many provide synapomorphies of clades of exemplars r epresenting genera in the Ingeae and Acacieae.