This volume starts with taxonomy. In the second part of the volume studies are presented about criteria that describe the performance of the lichen symbiosis. Part 3 deals with the subject "water relations in lichens". The articles of part 4 refer to the performance of lichens in various climates and habitats on earth. The studies collected in part 5 refer to the heat tolerance of lichens and to the repsonses of lichens to strong irradiance. This volume finishes with a description of the present state of changes in our European lichen flora and vegetation.