Metamerism,heterochrony, and inflorescence morphology of the Pithecellobium-complex (Leguminosae: Mimosoideae: Ingeae)

The diverse inflorescence morphology of species in the Pithecellobium-complex is shown to be a result of: 1) the organization of the components of the inflorescence and their relative positions; 2) the hierarchical relationship of the axes of the inflorescences and the position they assume in total tree architecture; and 3) heterochronic development of the components of the inflorescence. It is shown that the typological system of nomenclature of inflorescences leads to false assumptions of homology and therefore must be discarded. The morphology of inflorescences is discussed in terms of metamerism, and the term Repeating Growth Unit (RGU) is introduced and is defined as the smallest complete sequence of metamers produced by a meristem. A module is defined as the sequence of RGUs produced by a meristem. An inflorescence is defined as that sequence of metamers in an RGU which participates in the production and/or presentation of flowers and fruit. Heterochrony, proleptic and sylleptic buds, and shoot dimorphism are discussed and their role in modifying inflorescence morphology in the Pithecellobium-complex is illustrated. Examples from the Pithecellobium-complex are provided which demonstrate the various modifications of the inflorescence that result from the interaction of these various phenomena.