Genotypical and multiple phenotypical traits discriminate Salix × rubens Schrank clearly from its parent species

Most studies on Salix hybrids concerning the diversity in a hybrid complex included typical morphological characteristics of leaves, buds, twigs and flowers for comparison with genotypic traits. Our analyses are based on a set of phenotypical traits of 19 clones of the S. alba/S. fragilis-aggregate which includes characteristics as phenology, growth, and composition of secondary leaf compounds, for the first time additional to morphological traits. Three clearly distinct groups (S. alba L., S. fragilis L., and S. × rubens Schrank) could be identified based on phenotypical traits and ITS1 and 5.8S nrDNA sequences. S. × rubens revealed additivities at variable ITS1 and 5.8S positions as well as intermediate morphology and secondary compound pattern, but was characterised by significant earlier foliation start. This property leads to a better utilization of the vegetation period and may explain the detected better growth compared to the parent species and therefore also may have contributed to the widespread occurrence of S. × rubens in Central Europe.

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