Anatomical features of the leaves in the Dichrostachys group (Leguminosae: Mimosoideae) and their utility for phylogenetic studies

Abstract

Leaflet anatomy of 30 species in the genera Alantsilodendron, Calliandropsis, Dichrostachys, and Gagnebina, was studied using hand-sections, leaf clearings, and scanning electron microscopy. Variation was found in the distribution of stomata, venation patterns, and especially sclerification associated with the vascular tissue. Terminal idioblasts are common and diverse, with enlarged tracheids, tracheoidal elements, reticulate and pitted tracheids, and sclereids associated with the terminal veinlets. In addition, sclerification of bundle sheath cells was found in two of the genera, and non-terminal sclereids of unknown origin are reported in yet a third genus. Although many characters of leaf anatomy are strongly correlated with ecological factors, an evaluation of such characters in the context of a preliminary phylogeny indicates that they are useful in phylogeny reconstruction. The major limitation in the use of anatomical characters of leaves in phylogenetics seems to be the difficulty in defining discrete character states and not ecological plasticity.