Leaf anatomy of the three closely related legume genera Dichrostachys, Alantsilodendron, and Gagnebina was studied using clearings, thin sections, and scanning electron microscopy. Although many gross anatomical features parallel those reported in other mimosoid legumes, variation was found in the distribution of stomata, types of venation, and degree and distribution of sclerification. Stomata are densest on the abaxial surface in species of Gagnebina, while the opposite is true in Alantsilodendron. The distribution of stomata is closely correlated with nyctinastic leaf movements and the position of leaflets at night or under wilting conditions. Alantsilodendron is characterized by having mostly brochidodromous venation, with the exception of the anomalous A. villosum, which was the only species studied to have acrodromous venation. In contrast, species of Gagnebina display eucamptodromous venation and species of Dichrostachys s.s. vary from nearly eucamptodromous to brochidodromous. The cells terminating the veinlets are also highly variable. Some species have only enlarged tracheids, while others may have sclereids, reticulate or pitted tracheids, and tracheoidal elements. There is a correlation between degree of sclerification and aridity of the habitat in which a species is found. There are two major mechanisms by which leaves become sclerified in this group: 1. modification of conducting cells or 2. modification of bundle sheath cells. Perhaps the most striking result of this study is the variety of ways in which leaflets become sclerified, even among closely related taxa.

Key words: Alantsilodendron, Dichrostachys, Gagnebina, leaf anatomy, Leguminosae, Mimosoideae