Abstract: The genus Cyananthus is distributed in the Himalayan Floristic Subregion. In the early years, it was treated as a member of Polemoniaceae, but it is now generally regarded as a natural group of Campanulaceae. Made in this paper were a comprehensive comparative morphological study, a biometrical analysis of quantitative characters and an analysis of distri- bution pattern. The systematic position of the genus is discussed based on the evidence from pol- len morphology, chromosome number and external morphology. Finally the classification of the genus is revised. As a result of the character analysis, the evolutionary trends of the characters in Cam- panulaceae are suggested: superior ovary is a primitive state; the pollen grains have evolved from long-multicolpal to short-colpal, then to multiporate; the basic chromosome numbers have changed from 7 to 8 or 9, from which the groups with x=17 are derived (see Fig. 2), Fig. 2 illustrates that Cyananthus is the most primitive genus in the Gampanulaceae, closely related to Codonopsis, Platycodon, Leptocodon and Campanumoea. All these genera are rela- tively primitive in the family. The genus Cyananthus is distributed in S. E. Gansu (Zhugqu), W. Sichuan, S. and E. Xizang, S. Qinghai and N. W. Yunnan, extending westwards to Kashmir along the Himalay- as. Therefore, the genus is strictly limited to the Hengduan Mountains and the Himalayas. That is to say, it occupies the whole Sino-Himalayan Floristic Subregion (Fig. 3). This is of great importance for determining the limits of the floristic subregion, and for drawing a more acurate line between the Sino-Japanese Subregion and the Sine-Himalayan Floristic Subregion. The analysis of distribution patterns of species shows that the Hengduan Mountains is the di- stribution centre of the two major groups of Cyananthus, Sect. Stenolobi Franch. and Sect. Annui (Lian) Hong et L. M. Ma. In these two groups, only four out of 12 species, i. e. C. in- canus Hook. f. et Thoms., C. macrocalyx Franch., C. hookeri C. B. Cl. and C. inflatus Ho- ok. f. et Thoms., extend their areas westwards to Sikkim and Nepal. The other section, Sect. Cyananthus also exists in the west of the Hengduan Mountains. Although in the Himalayas oc- cur three major groups of the genus, only the last-mentioned group-Sect. Cyananthus is mainly distributed in the area (Fig. 4). According to the fact, we tend to infer that the Heng- duan Mountains is both the frequency and diversity centers of the genus Cyananthus. The genera of Campanulaceae, which are relatively primitive and the closest relatives of Cyananthus, all oc- cur in SW China and the adjacent regions. Therefore, the region may well be the preserved cen- ter of the primitive genera, or even may be the original center of the Campanulaceae. All data accumulated demonstrate that the genus is very old but still under intensive differ- entiation. With few diagnostic qualitative characters, the characters used in classifications are mostly quantitative ones. The following characters were usually used for classification of the genus: habit, plant size, leaf shape, leaf size, hairs on the leaf, corolla colour, petiole length, co- rolla length and hairs on the calyx, etc. Among them, only habit, corolla colour and hairs be- long to qualitative characters, and all of the others are quantitative ones. Because variation rang- es of quantitative characters have never been thoroughly studied in the previous classifications, some named taxa are artificial. An extensive statistical analysis of quantitative characters were carried out in the work to reveal their variation ranges. Based on this, 5 specific names are re- duced as synonyms: C. microrhombeus C. Y. Wu is reduced to C. delavayi Franch.; C. argenteus Marq. to C. longiflorus Franch.; C. pseudo-inflatus Tsoong to C. inflatus Hook. f. et Thoms.; and both C. neurocalyx C. Y. Wu and C. leiocalyx (Franch.) Cowan to C. macrocalyx Fr- anch., while C. montanus C. Y. Wu and C. Petiolatus Franch. are treated as subspecies in C. fl- avus Marq. and C. incanus Hook. f. et Thoms. respectively. As a result of the revision, 19 spe- cies and 2 subspecies are recognized in the present paper, with 7 species names and 15 variety names reduced. The genus is divided into three sections according to habit, corolla lobes and hairy types on calyx: Sect. Cyananthus, Sect. Stenolobi Franch. and Sect. Annui (Lian) Hong et L. M. Ma. In the present paper the chromosome number of the genus Cyananthus is reported for the first time, C. inflatus Hook. f. et Thoms. from Yadong, S. Tibet, being found to have 2n=14. And pollen morphology of the genus Leptocodon was first examined under SEM and is shownin Plate 1.