Form-functional trends in Spanish Umbilicariaceae with special reference to water relations

An attempt is made to interpret form-functional relationships in 20 Spanish Umbilicariaceae taxa based on results obtained during the last four years dealing with their anatomy, morphology and ultrastructure. Two principal form-functional trends were observed on water relations, depending on the physical state of water available: 1) a little-porous upper surface combined with rhizinomorphs when uptake is as liquid water or 2) a highly hygroscopic upper surface with no rhizinomorphs on the lower surface when the water uptake is as vapour. The medullary structure determined thallus porosity and influenced water storage capacity. The lichens studied were clearly differentiated by their ultrastructural features (relative quantities of the main intracellular organelles and structures), but interpretation of these patterns was unclear (...)