Anatomy and growth of the epiphytic cactus Epiphyllum phyllanthus under different radiation conditions

Background Plants develop mechanisms that confer tolerance to sun or shade exposure and the knowledge of their responses may help to devise strategies for the conservation of natural populations and their propagation. Aims We study the effect of shading on the ecophysiology and anatomy of Epiphyllum phyllanthus to determine its plasticity and tolerance. Methods Specimens of E. phyllanthus were subjected to full sun, 35%, 75%, and 85% shading for 60 days. The growth characteristics, phylloclade anatomy and water content in the plants were quantified and compared. Results All individuals subjected to full sun and 35% shading had died. A shading of 85% produced the highest fresh and dry mass of the stems. Higher shading caused no effect in the allocation of biomass to stems or roots or on the relative growth rate, net assimilation rate, leaf area ratio or water content. The thickness of the phylloclade increased with increased shading. The highest stomatal density on both surfaces was observed in the treatment with 75% shading. Conclusion E. phyllanthus is a sciophytic plant that requires shade to survive. Its main strategy appears to be the greater accumulation of water in its phylloclade under more shaded conditions, which stimulates plant growth.