Functional morphology of two Lepismium species (Rhipsalideae, Cactaceae)

Abstract

The morphology and anatomy of stem segments of 2 species of Lepismium (Cactaceae), which grow naturally in the Araucaria forest understory, in the state of Paraná, Brazil, are compared. The goal of this study was to identify morphological traits adapted to epiphytism and to the low light condition of the studied environment. Twenty-fi ve segments of Lepismium cruciforme and L. lumbricoides were collected and various morphological and anatomical features were measured. Differences (p < 0.05) were found between the species in mean values for total volume, total photosynthetic area, epidermis and hypodermis thickness, sclerenchyma area/total transversal area proportion of the stem segments and parenchyma area/total transversal area proportion, which can be correlated to their differences in shape. The xeric features found in Lepismium, most of them typical of drought-adapted cacti, have allowed the development of the epiphytic habit and the occupation of humid forests. As epiphytes, they are subject to some extent to water scarcity, although not to severe  conditions such as most terrestrial cacti. Mean values for hypodermis thickness, water content, amount of sclerenchyma and stomatal densities are more similar to mesomorphic plants, and can be correlated to epiphytism, showing that these species have lost some of their adaptations to dry environments.