Microhabitat and Structural Variation in the Aspicilia Desertorum Group (Lichenized Ascomycetes)

Fruticose and crustose forms of Aspicilia desertorum (Kremp.) Meresch. are recorded from Western Colorado in microhabitats beneath snow patches and on exposed rock surfaces, respectively. For single populations, microenvironmental variation in substrate, temperature, light intensity and water availability is directly related to continuous morphological variation. Functional variation with habitat is evident in growth form, stage of apothecial development, calcium oxalate pruinosity, anatomical disposition of unidentified crystalline material, cortical anatomy and continuity, numbers of algal cells per unit weight of thallus, medullary anatomy, maximum thallus water content (or water‐holding capacity) and relative thickness of hyphal walls. These multivariate relationships define ecomorphological syndromes and a pattern of variation with parallels at a higher phytogeographic level.