"Introduction (p. 1-2)

Amphibious lichens are widely distributed but little recognized components of freshwater vegetation. In most assessments of freshwater organisms however, lichens are still neglected which is partly due to the fact that corresponding literature is widely scattered and a profound treatment of these lichens in Central Europe is still missing.

This book is intended to provide a comprehensive tool for the determination of freshwater lichens in Central Europe for both, the non-specialized limnologist and the interested lichenologist. It further summarizes basic information on ecology and distribution. The book roughly covers an area ranging from the Alps to the south shores of the North and Baltic Sea and from the Western Carpathians in the east to the Vosgues-Mountains in the west. Amphi- bious lichens are found in springs, streams and rivers wherever hard and stable - land areas, lichens can represent the most diverse group of organisms covering virtually any rock surface (e.g. Frey 1922).

On the other hand, they are very rarely found in lakes. Rock surfaces incrusted by silt, surface erosion by sediment particles or water with a pH below 5 can exclude any growth of lichens. Resulting structure of a given watercourse, as well as they indicate key factors of water chemistry (Nascimbene et al. 2007). Water pollution was – and certainly still is – the main reason for the dramatic decline of lichen growth especially along larger watercourses during the past decades.

However, increasing water quality and reduced acidic impacts have enabled some species to recover even along the banks of large Central European rivers as for example the Rhine (Thüs 2006). Consequently, the potential use of lichens for bioindication purposes is regarded very high (Aptroot & Seaward 2003, Nascimbene et al. 2007, Thüs 2002). Unfortunately, the knowledge on ecology and indicator values of many freshwater li- - tain species is endangered or not are still sketchy.

Therefore, corresponding notes this, we hope that the present book will stimulate the recognition of freshwater lichens and promote the use of these organisms in matters of nature conservation. Lichens do not form a natural group of organisms (Liu & Hall 2004, Lutzoni et al. 2001) but represent an exceedingly delightful lifestyle in higher fungi, characterized by the symbiotic association with one or more photosynthetic partner(s) which supply the lichenized fungus with organic metabolites (Honegger1998).

More than 2000 species of lichen forming fungi occur in Central Europe, but only a much smaller number is found in and along watercourses. The lichen symbiosis is a nutrition strategy with an excellent performance under conditions characterized by frequent changes in water availability, the total lack of liquid water or extended periods of desiccation (Lange 2003a, b, Lange & Green 1997, Ried 1960a). On the other hand, ecosystems with permanent supply of liquid water are rather poor in lichen species (Ried 1960b).

In Central Europe, roughly a dozen taxa of lichens are able to survive under permanent submersion. In the splash water zone of watercourses and in temporarily inundated micro-sites the species number is much higher, reaching more than 100 taxa in upland areas. small river is permanent or ephemeral, and in large rivers the water level can."