Systematic Study On Daphne And Wikstroemia

Thymelaeaceae, a worldwide family which is found in both temperate and tropical region, chiefly in latitudes south of 40°N, includes ca. 45 genera, more than 800 species. Ten genera are found in China: Daphne L., Wikstroemia Endl., Aquilaria Lam., Edgeworthia Meisn., Rhamnoneuron Gilg, Eriosolena Bl., Stellera L., Stelleropsis Pobed., Thymelaea Mill. and Diarthron Turcz., including 115 species. The genus Daphne comprises about 95 species and 52 species distribute in China. The genus Wikstroemia comprises about 70 species and 49 species distribute in China. The taxonomy of the genera Daphne and Wikstroemia is controversial. No comprehensive systemic study on these two genera has been conducted previously. In this study, both morphological and molecular method were used to detect the phylogenetic relationship between the genera Daphne and Wikstroemia. The main results revealed in this study are as follows:1) We investigated their status by conduct clustering and principal component analysis with 32 morphological characters on 67 species from the genus Daphne and 64 species from the genus Wikstroemia. UPGMA clustering results reveal this two genera do not form monophyletic group. In the principal components analysis, the cumulative percent of the first three principal components presented 34.32%, while conventional taxonomic characters, the disc shape, phyllotaxy and the fruit type contribute minor effect on the first 3 components. So taxonomic distinguishable characters of this two genera cannot separate them clearly. Neither clustering analysis nor principal components analysis supports the traditional view of Daphne and Wikstroemia are natural monophyletic group.2) 56 species(variaties) of Daphne, 45 species(variaties) of Wikstroemia and 12 outgroups from Thymelaeaceae, with ten phenotypic characters were selected, to study the leaf epidermal microfeatures by using light microscopy. Results reveal that Daphne and Wikstromia are consistent in most of leaf features. The epidermal cells are polygonal and irregular in shape. The patterns of anticlinal wall are straight, curved and U shape. The cell sizes range in 30-40 μm×10-20 μm. Some species have singly hair in surface. Stomatal distribution is random, size range in 20-36 μm×17-25 μm, most are broadly elliptical and narrowly elliptical, stomatal frequency are 100-250S/mm2, and the anomocytic staomatal type is dominate. It is apparently that Daphne and Wikstromia share many stomatal and epidermal features., and no distinguishable features are suitable for separating this two genera. Results from epidermal characters analysis do not support Daphne and Wikstroemia are monophyly. Eriosolena should not be include in the genus Daphne for the special papillae only found in Eriosolena composita rather than in other genera of Thymeleaceae. In compare with other genera, Rhamnoneuron, Eriosolena, Stelleropsis, Daphnopsis and Edgeworthia in Thymelaeoideae, Daphne and Wikstroemia might be derived and origined latter based on the stomatal features.3) The Molecular phylogenetic analysis on 14 species(variaties) of Daphne, 14 species(variaties) of Wikstroemia and 5 species of outgroup include Aquilaria sinensis(Lour.) Spreng., Rhamnoneuron balansae(Drake) Gilg, Edgeworthia chrysantha Lindl., Stelleropsis altaica(Thieb.) Pobed. and Stellera chamaejasme L. are studied by using nrDNA ITS region sequences. It shows that Daphne and Wikstroemia do not form monophyletic group, and there are mixed species in this two genera, further study shoud be done to reclassification this two genera, for our material and method are limited in this study.