Insights into the Taxonomically Challenging Hexaploid Alpine Shrub Willows of <i>Salix</i> Sections <i>Phylicifoliae</i> and <i>Nigricantes</i> (Salicaceae)
2023
Natascha D. Wagner | Pia Marinček | Loïc Pittet | Elvira Hörandl
The complex genomic composition of allopolyploid plants leads to morphologically diverse species. The traditional taxonomical treatment of the medium-sized, hexaploid shrub willows distributed in the Alps is difficult based on their variable morphological characters. In this study, RAD sequencing data, infrared-spectroscopy, and morphometric data are used to analyze the phylogenetic relationships of the hexaploid species of the sections <i>Nigricantes</i> and <i>Phylicifoliae</i> in a phylogenetic framework of 45 Eurasian <i>Salix</i> species. Both sections comprise local endemics as well as widespread species. Based on the molecular data, the described morphological species appeared as monophyletic lineages (except for <i>S. phylicifolia</i> s.str. and <i>S. bicolor</i>, which are intermingled). Both sections <i>Phylicifoliae</i> and <i>Nigricantes</i> are polyphyletic. Infrared-spectroscopy mostly confirmed the differentiation of hexaploid alpine species. The morphometric data confirmed the molecular results and supported the inclusion of <i>S. bicolor</i> into <i>S. phylicifolia</i> s.l., whereas the alpine endemic <i>S. hegetschweileri</i> is distinct and closely related to species of the section <i>Nigricantes</i>. The genomic structure and co-ancestry analyses of the hexaploid species revealed a geographical pattern for widespread <i>S. myrsinifolia</i>, separating the Scandinavian from the alpine populations. The newly described <i>S. kaptarae</i> is tetraploid and is grouped within <i>S. cinerea</i>. Our data reveal that both sections <i>Phylicifoliae</i> and <i>Nigricantes</i> need to be redefined.
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