Diversity of the willow complex salix alba - s. x rubens - s. Fragilis

A comparative phenotypic and genetic analysis was performed to investigate the variation within the S. alba – S. x rubens – S. fragilis complex in Flanders (Belgium). Multivariate analyses revealed the division of this willow complex into two main groups containing (i) S. alba and S. x rubens and (ii) S. fragilis and S. x rubens var. basfordiana. Moreover, the genetic similarity between S. x rubens and S. x rubens var. basfordiana was lower than between either taxon and S. alba or S. fragilis, respectively. These findings were unexpected as S. x rubens and S. x rubens var. basfordiana are classified as hybrids of S. alba and S. fragilis. The phenotypically distinguishable varieties of S. alba and S. fragilis did not cluster separately, indicating that they are not genetically differentiated. All varieties displayed a significant level of genetic distance between the individuals, contradicting the clonal nature of some varieties, as has been suggested before.