Primary Study Of Systematics In Sorbus

The genus Sorbus of the Rosaceae, comprising ca. 100 species, is distributed mainly in Asia, Europe and North America of the Northern Hemisphere. Six subgenera, Subg. Aria, Subg. Chamaemespilus, Subg. Micromeles, Subg. Torminalis, Subg. Cormus, Subg. Sorbus are generally recognized in this genus in the broad sense and some subgenera are taxonomically poorly known due to the lacking of field observation and the scantiness of herbarium specimens. In addition, the scope of Sorbus s.l. and its systematic position are not yet clear, and remain to be studied. In this paper, the phylogenetic relationships of this genus and its related groups were dealt with mainly basing on the evidence from morphology and molecular systematics. The results were summarized as follows:1. Cladistic analysis and phenetic analysis34 species representing six subgenera in Sorbus s.l., and five outgroups, Pyrus, Crataegus, Photinia, Malus and Cotoneaster, were sampled to investigate the infrageneric relationships by means of the cladistic and phenetic analysis based on 30 morphological characters. The results indicate that Sorbus s.l. was entirely not a monophyly, and outgroups were nested in the genus. Infrageneric groups can also not form a monophyly, only subg. Sorbus with pinnate leaves seems to constitute a cluster. Therefore, the infrageneric relationships should be studied by adding more morphological characters of taxa or by a molecular systematic approach.2. Molecular systematicsPhylogenetic relationships of 23 species of the genus Sorbus were investigated using maximum parsimony analyses of sequence data from nrDNA ITS and cpDNA trnL- trnF spacer. Phylogenetic tree was constructed for five subgenera in Sorbus s. l. and its related groups. The results of parsimony analysis suggest that in Sorbus s. l. is not a monophyletic group because its outgroups were nested within different major clades in the phylogenetic tree. Subg. Aria forms a monophyletic group with high bootstrap values. We concluded that Aria is probably more closely related to...