In the present thesis, a detailed review of the literature was given on the Betulaceae. Some new data was provided based on the author’s studies in order to analyze various characters, such as inflorescence, flower, pollen and leaf epidermis, among the genera treated. The polarity of the characters was determined according to the criteria of outgroup comparison and compatibility analysis. A cladistic analysis was made using the methods of Maximal Same Steps and Minimal Parallel Evolution developed by Xu (1993). The generic distributions in both modern and fossil times were outlined, and their distribution center, place and time of origin and the way of dispersal were discussed. An attempt was made to discuss early differentiation, geographical radiation and morphological evolution of the family on the background of paleogeography and paleoclimatology, tracing back as far as the Late Cretaceous and Early Tertiary. Finally, supraspecific taxa, from section to tribe, were systematically arranged.

The present paper reports the chromosome numbers and karyotypes of nine species and one variety of Heracleum in the Hengduan Mountains of South-western China. Among them the somatic chromosome number and karyotypes of seven species and one variety are reported for the first time. Their chromosome parameters and karyotypes formulae are shown in Tables 1, 2, and their karyotypes and idiograms are shown in Plates 1, 2 and Fig. 1. The chromosome number of all the species is 2n=2x=22 except H. millefolium var. longilobum, which has both 2n=22 and 2n=24 (see Plate 2: T--W). The karyotypes of the nine species and one variety of Heracleum consist of metacentric and submetacentric chromosomes. The karyotypes of two species, H. wolongense and H. stenopterum, belong to “lA” type, while the karytypes of the rest belong to “2A” type in Stebbins¹ classification. Four species have two chromosomes with satellites. And one B-chromosome is discovered in somatic cells of some H. vicinum individuals (see Plate 1: G). Classification is discussed based on the analysis of the chromosome number and karyotype of Heracleum. The cytotypes are found different between H. millefolium var. millefolium and H. millefolium var. longilobu. The karyotypic formula of the former one is K (2n) = 22 = 18m+4sm, whereas that of the latter is K (2n) = 22 = 16m+6sm and K (2n) = 24= 18m+6sm. They also differ from one another in order number of the submetacentric chromosomes. Although they are small low-growing plants and have 3-4 pinnatipartite leaves and seem closely related, they differ greatly in length and density of arrangement of the ultimate lobelets and in indumentum of ovaries. Under SEM, the sculpture pollen exine is shown differentiated between the two varieties. Hence it is suggested that H. millefolium var. longilobum be treated as an independent species. Furthermore, based on the interspecific relationship and variation in chromosome number and karyotypic symmetry, the hypothesis is proposed that the genus Heracleum has been evolving in two directions, from diploid to polyploid and from symmetrical to asymmetrical in karyotype. Finally, according to the data available the correlation is found between the change of chromo-some number and karyotypic symmetry on one side and the latitudinal distribution of the genus on the other, as 26 species and one variety of Heracleum occur in the Hengduan Mountains, and their external morphological characters and cytotypes have differentiated distinctly, it is considered that the Hengduan Mountains is both the center of frequency and the center of diversity of Heracleum. Moreover, we speculate that the Hengduan Mountains or the Caucasus is the original center of this genus.

Recently the authors applied the chromosome image analysis in the study of Brassiceae and obtained the following results. 1. The authors apllied the image analysis for the first time in the study of the karyotype of 13 species of Brassiceae. The karyotype data. karyograms, idiograms and karyotype formulae of Raphanus sativus var. raphanistroides and Sinapis alba are reported in this paper. 2. The authors have established the database of chromosome image analysis of Cruciferae, including five genera and 13 species. This is the first database of chromosome image analysis of Cruciferae in China and abroad. 3. The authors applied the database of chromosome image analysis for the first time in the taxonomical studies of Brassiceae, for example, to study the relationship and evolution of some species of Brassica. As a result they got some karyotype data which might be useful to plant taxonomists. It is suggested that the database of chromosome image analysis be very useful to the plant taxonomical studies.

A taxonomic revision of the genus Lasianthus Jack in China is presented. Thirtyone species including four subspecies and ten varieties from China are recognized, of which eight new combinations, one new species, one new subspecies and two new varieties are established, and nine species are recorded as new to China; and also twelve specific names are reduced as new synonyms. Some mistakes and confusions in the genus existed mainly in Chinese botanical references are rectified and clarified.

Nine new species and twelve new varieties of Athyriaceae from the Hengduan Mountains, China, are described.

Two new species of the genus Aleuritopteris (Sinopteridaceae), A. humatifoliaX. C. Zhang et L. Shi and A. ebenipes X. C. Zhang, are described from Southern and Southwestern China. A. cremea Ching is redescribed and illustrated in the present paper. In addition, a key is also given to the species which are confused with A. cremea Ching in the genus.

This paper describes a new species, Stigeoclonium ovisporum Wei (Chaetophoraceae, Ulotrichales), from Yunnan and Sichuan provinces, China. In asexual reproduction of this alga, narrow oviod sporangia produce zoospores. The differentiation of vegetative cellsand reproductive ones is an advanced character in the genrus Stigeoclonium.