AN UNUSUAL EPICUTICULAR WAX ULTRASTRUCTURE ON LEAVES OF PROSOPIS TAMARUGO (LEGUMINOSAE)

Studies of Prosopis tamarugo Phil. leaflet surfaces by scanning and transmission electron microscopy disclosed an aggregate coating of basic wax structures of various shapes along with large semi-vertical plates. The basic structures, with some degree of variation, were also present on P. velutina Woot. and on several other Prosopis species which had been previously investigated. However, the plates, about 3 μm in size, were observed only on P. tamarugo. The basic wax structures were first observed on very young leaflets, about 6 h after emergence from the apical bud. The plates appeared after 24 to 72 h. Both plates and basic structures were larger on seedlings grown in a low (20–25%) relative humidity as compared to high (70%) humidity. When grown side-by-side in the greenhouse, leaflets of P. tamarugo seedlings were more isolateral in structure than those of P. velutina, suggesting a greater xeromorphic adaptation. The unusual epicuticular configuration described could be a mechanism that enhances the foliar absorption of atmospheric moisture, or at least minimizes cuticular transpiration, thereby aiding survival of this unique tree in its native habitat of northern Chile.