Biosystematic Studies On Aster Ageratoides (Asteraceae) Polyploid Complex

Aster ageratoides polyploid complex is widely distributed in China, as well as in Japan, Northeast Asia and the south of the Himalayes. The complex has been reputed to be a difficult taxonomical subject.According to Ling Rong (1985), 2 species and 13 varieties are known in China. These taxa are very difficult to be distinguished. The taxonomic confusion in the complex comes from the fact that very little is known of its diversity and complexity in morphology and cytology.Based on extensive field observation and population sampling in 71 populations of 20 provinces, this dissertation investigates morphology, ecology, cytology, cytogeography and ITS sequences of this complex. The results show that A. ageratoides polyploid complex might be originated in Northeastern China, from which it migrated along three different routes. The distribution center of the complex is situated in the area from the Yunnan-Guizhou Plateau to Daba Mountains. Six varieties are recognized, and the other six varieties and one intergeneric hybrid are described here as new. The systematic relationships between varieties were inferred. The main results and the essential points are summarized as follows. 1. MorphologyThe diversity of rhizome and some other characters, which have been neglected by former researchers, are revalued and their systematic significance is pointed out and confirmed. On the other hand, some characters used by the previous authors for distinguishing the varieties are extremely variable both within and among populations, but they are important in studying the evolution of the complex. Theevolution of morphological characters in this complex is discussed.2. Clonal Plant EcologyA. ageratoides complex is a clonal plant. Its growth form can be divided into phalanx, middling form and guerrilla.When some diploid plants of var. scaberulus, which belong to phalanx decreases in population density because of competition between the two varieties with different clonal growth. The diversity of clonal growth forms has exerted tremendous influence on the distribution of this complex in the middle and lower reaches of the Changj iang River.The sheathes of rosulate leaves in two varieties are marcescent because of their unusual life history.3. CytologyThe chromosome numbers and karyotypes of 65 population of this complex were investigated. The results show that there is a polyploid series from 2x to 4x, 5x, 6x,and Sx.And karyotypic differentiation, polyploidization and hybridization are the main evolutionary forces in the complex.4. CytogeographyResults of my study on the distribution pattern of Chinese Aster ageratoides polyploid complex were not in agreement with Chen'(1992). Distribution zone of diploid individual are the most extensive in china, while no tetraploid plant is found north of 40 degree north latitude, and hexaploid populations distribute mainly along the Changj iang River, is found only in three populations in the Yunnan-Guzhou Plateau.The hexaploid cytotype of var. laticorymbus might be originated in the Yunnan-Guzhou Plateau, and then migrated southeastwards to the south areas of the Chanfjiang River. The tetraploid cytoype of var. scaberulus might originate inEastern China, expanding northwestwards to the Yunnan-Guzhou Plateau and Sishun. The intervarietal crossing has taken place in low frequency when the two varieties are sympatric.5. ITS sequenceOf 19 population used in the analysis of ITS sequences, 17 are from A.agenatoides complex, 1 from a new species, A. jishouensis, and 1 from Kalimeris indica. Based on these ITS data, a cladistic analysis is carried out (PAUP software). The result show that there are close phylogenetic relationships among var. laticorymbus, var. gerlachii and var. astropurpurea. These varieties all can be found in the Yunnan-Guzhou Plateau which might be a secondary differentiation center. ITS data supported the point of view that take var. scaberulus, which distributes extensively in the south China, as natural taxon. But they didn't su...