Leaf anatomy of six arboreal eudicotyledons species growing along an altitudinal gradient on the high basin of the Tocuyo river, Venezuela

Riparian forests are known to be critical environments for biodiversity maintenance. The leaf anatomy of Sapium glandulosum (L.) Morong., Bauhinia aculeata L., Inga vera Willd., Pithecellobium dulce (Roxb.) Benth., Guazuma ulmifolia Lam. and Cecropia peltata L., growing along an altitudinal gradient (682–800 – 1030 m a.s.l.) on the high basin of the Tocuyo river were studied, in order to evaluate the possible foliar phenotypic plasticity that makes possible their adaptation at this altitudinal range. Leaf blade samples were collected from adult trees growing at two different altitude; these samples were fixed in FAA and processed using classical techniques in optical microscopy. The leaf histology was similar at both altitudes for all taxa, but differences were detected between them on quantitative anatomic characteristics, which varied depending on the species. The features with higher plasticity were: adaxial stomatal density (amphistomatic leaves), trichome density, palisade parenchyma thickness and leaf thickness. I. vera seems to be the taxon in which lower plasticity in the blade’s anatomical characters was evident, while G. ulmifolia was the species with the highest phenotypic plasticity in the altitudinal gradient, showing more heliomorphic characteristics as altitude increased, which confers it adaptive advantages to this species for colonizing riparian forest ecosystems.