729 
Branch apices, heterochrony, and 
inflorescence morphology in some mimosoid 
legumes (Leguminosae; Mimosoideae) 
James Grimes 
Abstract 
Grimes, James (Harding Laboratory, Neiu York Botanical Carden, Bronx, NY W458 USA) 1996. Branch 
apices, heterochrony and inflorescence morphology in some mimosoid legumes (Leguminosae: Mimosoideae). 
Telopea 6(4): 729-748. Six species of mimosoid legumes, Paraserianthes lophantha, Zapoteca tctragona, 
Lysiloma microphyllum. Acacia nilotica, Ebcnopsis ebano, and Pithecellobium duke, are subjects of a 
study of morphology of inflorescences, branch-apices, and terminal and axillary buds. Differences 
in patterns of growth in the species can be attributed to shoot-dimorphism, phyllotaxy, and 
heterochronic differences in development of stipules and unit-inflorescences. Species form only 
long-shoots or one of two kinds of short-shoots. One kind of short-shoot is formed in a series 
from an axillary meristem, and is ephemeral if it produces inflorescences. The other is solitary 
and long-persistent. Inflorescences were found to be produced either on the long-shoots or the 
short-shoots, but not on both. All inflorescences can be described as pseudoracemes of 
unit-inflorescences, but differ depending on whether the unit-inflorescences arise from 
long-shoots or short-shoots, and on whether there is heterochronic development of 
unit-inflorescences and subtending leaves. The unit-inflorescences develop from primary buds 
or from secondary buds. Phyllotaxy is either spiral or distichous. Stipules arise either on the 
flanks of the leaf-primordium, or from primordia spatially independent, but concomitant 
with the leaf-primordium. 
Introduction 
An earlier study (Grimes, 1992) of the inflorescence morphology of a group of 
mimosoid legumes informally called the Pithecellobiiim-complex (Leguminosae: 
Mimosoideae: Ingeae) showed that inflorescence morphology is determined not only 
by the relative arrangement of organs, but also by heterochronic changes in their 
development. It was also shown that inflorescence morphology is a reflection of the 
branch morphology, and ultimately of the plant architecture. Most of the differences 
found in inflorescence- and branch-morphology were attributed to branch 
dimorphism and to heterochronic differences in timing of development of the 
leaf-primordia and axillary buds. A subsequent paper (Grimes 1995) presented a 
phylogenetic analysis of tribe Ingeae (including representatives of Acacieae). The 
data set for the analysis included a number of characters, or hypotheses of homology, 
reflecting some of these morphological and heterochronic differences in inflorescences. 
This paper continues the study of inflorescence morphology in Ingeae, with particular 
reference to timing of development of the component organs and the formation and 
development of axillary buds. Specifically, is there a generalized pattern of 
development such that differences in inflorescence and branch morphology might 
be attributed mostly to heterochronic phenomena, or are these differences due in 
part to differences in pathways of development? 
Implicit in my approach is the view that if developmental pathways are shared between 
two species, the developmental pathway is a character (De Queiroz 1985), that 
modifications of these pathways can be seen as states of the character, and that 
'character' and 'character-state' are hierarchy-dependent. That is to say a character at 
