LUCKOW, MELISSA. L. H. Bailey Hortorium, 462 Mann Library, Cornell University, Ithaca, NY 14853. - Leaf anatomy of three genera of Malagasy mimosoid legumes: adaptations to xeric habitats.
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