Variation of leaf shape of Salix herbacea in Europe

The morphology of Salix herbacea leaves was examined to find possible reasons for the observed intra-specific morphological variation. Seventeen samples were collected from the following regions: the Southern and Eastern Carpathians, the Northern Carpathians, the Alps: Eastern, Central and Western, the Pyrenees, Western Scandinavia, and Northern Scandinavia. The leaves were dried in an herbarium, scanned and measured. A total of 3,890 leaves from 503 individuals were statistically analyzed. The analyses were based on the shape-describing characters. A notable variation of shape characters of leaves of S. herbacea was found on different levels: intra- and inter-individual, between samples and between regions. The local environmental conditions did not affect the leaf shape much, but the regional climatic factors influenced them statistically significantly. The most important factor—the summer precipitation—was positively correlated with leaf elongation, while the mean wind velocity was negatively correlated with leaf elongation. The latter was also positively correlated with the tooth number. The hypothesis that glacial migrations and isolations of S. herbacea populations were responsible for the contemporary morphological differentiation of the species was not confirmed; however, some similarities between the biogeographical structures revealed in the previously published results of molecular analyses and in the present morphological study were also noticed.