Systematic Studies On Genera Sterigmostemum And Matthiola In Brassicaceae

Sterigmostemun M. Bieb. and Matthiola R. Br. belonged to Trib. Hesperideae and Trib.Matthioleae respectively in Brassicaceae, the species classification in each of the two genura showedcontroversial issues in “Flora of China (Chinese)”,“Flora Xinjiangensis” and “Flora of China(English)”. The difference in specimen identification and the limitation of traditional morphologicalcharacteristics might be the main reason causing these debates. Thus, combining seedmicro-morphology, pollen morphology, karyotype and molecular phylogenetic development, weanalyzed the systematics of each genus, in order to offer data support for identifying the phylogeneticposition of each genus and the scope of species in each genus.(1) Pollen morphology of eight species of Sterigmostemun. The results showed that the pollengrains of all observed species were prolate (P/E=1.33–1.84), tricolpate (3germinal apertures) withfurrows almost extending to the poles. They were elliptic from equatorial view and oval from polarview. Pollen grains had reticulate sculpture and rarely wide-reticulate, the mesh of reticulate sculptureshowed irregular polygon. Some differences of the quantative characters of pollen grains existedamong eight species. Based on the reticulate type or the depth of germinal aperture, the pollens ofeight species could be divided into two groups. In total, there were no consistant rule of pollenmorphology at genus level, therefore, there were also no evidence support the view that S. violaceum,S. fuhaiense, S. incanum were the same species, and S. grandiflorum and S. eglandulosum were thesame species in “Flora of China (English)”.The results of phylogenetic analysis of eight species of Sterigmostemun showed that the alignedlength of ITS sequence was641bp, and there were360parsimonious informative sites and57.5%G+C content in the ITS sequence. The aligned length of trnL-F sequence was822bp, and there wereonly9parsimonious informative sites and31.8%G+C content in the trnL-F sequence. In comparison,ITS sequence (56.2%) contained more phylogenetic information than trnL-F sequence (1.1%). TakingMatthiola stoddarti Bge. as the outgroup, eight species of Sterigmostemun were are separated into twogeographical groups in ITS trees based on both MP and NJ methods: Junggar Basin group (S.fuhaiense, S. tomentosum, S. sulfureum, S. violaceum) and Altun mountain group (S. matthioloides, S.grandiflorum, S. incanum, S. eglandulosum), which corresponded with the collection sites of plantsamples. In the MP and NJ trees based on trnL-F sequence, S. tomentosum clustered in completelydifferent groups with other seven species, but the seven species showed the same result with that ofITS. Consequently, ITS sequence indicated the significant influence of the geographic isolation onnucleargene during species divergence, while trnL-F sequence revealed that there might be differentevolutionary pathways or directions of chloroplast DNA between S. tomentosum and other seven species. To a certain degree, the result based on trnL-F sequence supported the view that only S.tomentosum should be still kept in “Flora of China”.(3) Systematic classification of three species of Matthiola. The results showed that the there weresome differences on traditional morphology and seed micro-morphology of M. stoddarti, M. incana,M. chorassanica. Karyotype analysis indicated that the karyotype of M. stoddarti and M.chorassanica were both2n=2x=12, while that of M. incana was2n=2x=14. The pollen morphology ofthree species was similar at a certain degree. The pollen grains of M. stoddarti and M. chorassanicawere tricolpate (3germinal apertures), their mesh ridge widths were both0.32μm, and the luminadiameter were similar,1.38and1.58μm, respectively. In comparision, the pollen grain of M. incanawas not obvious, and itse lumina diameter was less that the fomer two species. ITS sequence analysisshowed that M. stoddarti and M. chorassanica had relatively nearer evolutionary distance than thatbetween M. incana, i.e. the relations among the fomer two species these species were closer. Inconclusion, this study did not support the viewpoint that M. stoddarti was moved from genusMatthiola in “Flora of China (English)”; the all three species retained in genus Matthiola should bemore proper.