|其他摘要||The tribe Mutisieae Cass. is considered as one of the most important tribes for understanding the systematic relationships in the Compositae as it is a basal lineage in the family. In southern America the greatest concentration of genera and species is found along the southern Andes, however there are still many key genera distributed in eastern Asia including the Nouelia group, Pertya group and Gerbera complex. Phylogeny of Mutisieae in eastern Asia was reconstructed by means of integrative methods involving palynology, comparative embryology, anatomy, and molecular systematics which were based on four DNA sequences. The emerging time and the diverging time of those genera were evaluated using fossil records and the molecular clock. Phylogenetic relationships among genera and some species were addressed, mainly based on the results of molecular systematics. Biogeography of those genera was discussed. Major results of the dissertation were summarized as follows:
Pollen morphology of 27 species and one variety representing seven Asian genera and the southern American Gochnatia of the tribe Mutisieae Less. in the sense of Bremer (Compositae) was investigated by scanning electron microscopy and light microscopy. The pollen grains are usually radically symmetrical, isopolar, and tricolporate. The shape varies from spheroidal to subprolate in equatorial view, and is three-lobed circular in the polar view. Based on exine sculpturing observed under SEM, the pollen grains can be divided into three types, i.e. (i) type I, with macrogranulate sculpture; (ii) type II, with a finely granulate sculpture, and (iii) type III, with spiny sculpture. The palynological data showed that the Macroclinidium Maxim. was remarkably distinguished from the other seven genera. The variation of pollen characteristics within the Mutisieae in Asia is little at the species level, but it proves some useful information for studying the relationships among genera. Further study with broader sampling at the genric level is needed for further understanding of the evolutionary history of the Mutisieae.
We described and compared the characters of embryological development from both Asian species ie. Nouelia insignis and Leucomeris decora (=Gochnatia decora), in order to infer ontogenetic transitions that occurred during the early phases. The analyses indicate that N. insignis and L. decora resemble each other, in having only one row of microspore mother cells in each microsporangium, three layers of anther wall and each layer comprising sole layer of cells. The feature of one row of microspore mother cells is somewhat unique compared with microsporangia in other angiosperms and is likely an apomorphy of the common ancestor of N. insignis and L. decora. They also share the following features. Glandular tapetum is with one nucleus. The ovule is anatropous, unitegmic and tenuinucellar. Eight-nucleate embryo sac is of “Polygonum” type. However, they differ from each other mainly in their androecium developments, among which, the tapetum of N. insignis crushed earlier than that of L. decora. Both successive type and simultaneous type of cytokinesis present in the meiotic divisions of microspore mother cells in N. insignis, but only successive type in L. decora. The results show that many of these characters are similar to each other and support the sister relationship of N. insignis and L. decora. Some embryological characters revealed that both L. decora and N. insignis are from an archaic lingeage.
Leaf epidermis of 31 species belonging to 12 genera of Mutisieae from both eastern Asia and southern America was investigated. It was shown that the stomatal apparatus was mainly staurocytic and anomocytic and presented in abaxial epiderimis of all species and in the adaxial epidermis of some species. The leaf epidermal cells were with little difference among species but can serve as a criterion for distinguishing genera. The leaf epidermal cells were usually irregular or polygonal, with the anticlinal walls straight, arched, sinuolate, sinuous to sinuate. The major shapes of stomatal apparatus were elliptical or nearly rounded, the inner margin of the outer stomatal rim ranged from nearly-smooth to sinuolate or erose, among which the outer stomatal rim of Macroclinidium were two pairs and quite different from other species. The surface is mostly smooth and no waxy or corneous types, however there are some species with surface covered with ridges of wax or waxy types.
Molecular phylogeny of eastern Asian Mutisieae was elucidated using ITS、ndhF、trnL-F and rpl16 sequences. It was shown there were no close affinites between the eastern Asian Leucomeris and the southern American Gochnatia, and therefore Leucomeris should be resumed. Leucomeris decora and Nouelia insignis are sister to each other and occupy an isolated position in the basal lineage together with some south American genera, and this basal lineages were the so-called “Stifftia Group”. Ainsliaea was supported as a monophyletic group and formed a natural genus; however the sectional divisions within the genus were artificial as none of the sections was supported in the all MP trees. Based on the morphological and molecular evidence, we suggested that Myripnois should be merged into Pertya and therefore only three genera were included in Pertya group. The results support the viewpoint of Wu (2002) and Jefrey (1967) that Piloselloides should be separated from Gerbera and resumed. However, the relationship of Gerbera and Leibnitzia was not resolved. Based on the morphological and molecular evidence, the viewpoint of Hansen (1990) was somewhat supported that the two genera should be merged. However more samples were needed to support this viewpoint.
Using a molecular clock, the relative divergent time of major groups in the eastern Asian Mutisieae was estimated. Based on calibration results and the statistical analyses of the geographical distribution, the formation of patterns of the geographical distribution of those groups were discussed. The result implied that the tribe Mutisieae is of neotropic origin. The ancester of Nouelia group was dispersed into the southwest of China along North American and Beringia or North Atlantic landbridge, then surviveing in there during the Quaternary Glaciation and diverged into two genera afte the Quaternary Glaciation. The Gerbera complex was diverged in two major routes, the first one dispersing into the Central America and South America and evolving Chaptalia、Trichocline etc., the other lineage migrating through Beringia into East Asia and Africa with some genera differentiated in the Southwest of China after the Quaternary Glaciation then migrating toward the north later. The Pertya group was distributed in East Asia, which may have the same ancestral group with some African genera and formed an eruptive divergency due to the climate change after Quaternary Glaciation.|