This book presents not only a comprehensive description of the 32 willow species native in Austria plus their hybrids, but also a general survey of the genus Salix world-wide. Fossil records indicate origin of Salix in early Tertiary. Distributional patterns, breeding and dispersal systems, and molecular data suggest that geographical and ecological isolation has been the most important factor for speciation. A historical survey of classification schemes and recent molecular analyses show low congruence of major groups. A sectional classification, which might reflect natural relationships better than present subgeneric concepts, is presented for the Austrian taxa. Features of germination and seedling development help to explain the preference of willows for open, unshaded, wet pioneer habitats. The habitats of the Austrian species are compared and grouped according to altitude and pH of substrate. For alpine species, this grouping is strongly correlated with distributional patterns within the Eastern Alps, the lowland taxa being usualy more widespread. Taxa with similar distributions are grouped in chorological types. Closely related species within a section have vicariant distributional areas and different habitats. Secondary metabolites of Salix include the prominent phenol glucoside salicin and its derivate, salicylic acid. Stem bark of Salix has been used as a pain killer and remedy against fever in traditional medicine. Only recently its value has been rediscovered in phytotherapy against chronic rheumatism, where it outperforms synthetic products because of lower side-effects in long-term treatments. Besides phenolic glucosides, other important classes of compounds include phenolic dimeres, phenolic acids and flavonoids. Many microbial and insect herbivore predate on willows. Besides various bacterial and fungal pathogens, beneficial microorganisms, such as arbuscular and ectomycorhizal fungi, also occur. Specific secondary metabolites also function as antimicrobial and herbivore defenses and their sequestration by larvae of specialized leaf beetles as defense against parasites. Gall-forming wasps and midges use willows as their host. The usage of willows has a long history. Beside traditional use as braiding material, willows are nowadays important in soil-bioengineering and plant technology. Because of high ability to sprout from cuttings, rapid vegetative growth and high elasticity of branches, willows are used for stabilizing riversides and steep slopes, for fences and other living sculptures, and for ornamental use. Some species are cultivated for biomass productio. For recognizing species, different determination keys for each season are necessary. Leaves in summer and autumn show the most important species-specific characters. In spring willows can be determined by features of male or female catkins, in winter condition by buds and twigs. The Austrian species are described, including diagnostic characters, variation and taxonomy, flowering time, chromosome numbers, distribution and ecology in Austria and adjacent regions, endangered status, general distribution, and usage. All species are shown with detailed colour photos that illustrate the special features of each taxon. Hybridization in willows has been over-emphasized in the past, but might be still problematic in some species, especially in the case of backcrossing. Frequent use of cultivated hybrids makes it difficult to estimate the frequency of spontaneous hybridization. Abundancy estimates of hybrids in Austria suggest that close relationships, same ploidy level, and a strong overlap in the altitudinal distribution of the parental species are main factors that promote hybridization. Some tips for recognizing hybrids in the field, short descriptions, photos of the most common hybrids in Austria and a list of binomial names are provided.
