Saxifraga L., the largest genus (ca. 460 spp.) in the family Saxifragaceae, is widely distributed across Europe and Asia, mainly in the Alps and the Sino-Himalayan area, with extensions in the Rocky Mt / Andean Cordillera south to Tierra del Fuego. The genus displays remarkable morphological variation. Phylogenetic analyses were conducted to test previous classifications. Molecular evidence comprised DNA sequences from the chloroplast gene (matK) and nuclear regions (ITS and Duo1). The sequences were also used in plant identification. In many cases genetic distances between species in terms of DNA sequences were very low, indicating rapid evolution. Morphological evidence, including microscopic characters from pollen nuclear number, exine and leaf venation, was also collected. Phylogenetic trees were produced from the molecular data, the morphological data and from the combined data. Morphological data improved resolution in the molecular trees. The phylogenies were in substantial agreement and suggested that a few taxonomic realignments and new combinations are needed to make the sections and subsections monophyletic. A revised classification of Saxifraga primarily to subsection level is presented. The main changes from previous classifications are: (1) genus Saxifragella is included as a monotypic section in Saxifraga; (2) sect. Ciliatae subsect. Serpyllifoliae is merged into sect. Ciliatae subsect. Rosulares; (3) sect. Ciliatae subsect. Cinerascentes is merged with subsection Gemmiparae; (4) section Porphyrion is monophyletic only if S.mutata and S. florulenta (formerly in sect. Ligulatae) are included; this transfer also makes sect. Ligulatae monophyletic; (5) S.mutata and S.aizoides (the later formerly in sect. Xanthizoon) are closely related and are now placed together in ser. Xanthizoon of sect. Porphyrion. The geographical distributions of the basal sections of the genus, i.e. Irregulares, Heterisia, Saxifragella and Trachyphyllum suggest an origin of the genus around the shores of the Pacific Ocean, probably in the Beringian area.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:574134 |
| Date | January 2013 |
| Creators | Zhang, Zhuoxin |
| Contributors | Gornall, Richard; Schwarzacher, Gertrude |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/28041 |
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