Geographical distribution of Kengyilia Yen et J. L. Yang (Poaceae)
以礼草属的地理分布

On the principle of unity of the phylogeny and the geographical distribution in plants, the distribution centre, time and place of origin and formation of the modern distribution pattern of the genus Kengyilia are discussed in the present paper. Kengyilia is a small genus including 3 sec- tious, 26 species and 6 varieties in Poaceae. The genus is distributed in China, Kazakhstan, Kir- ghizia, Tadzhikistan, Afghanistan and Iran. It adapts to the temperate habitats, and also exists in the environments of high elevation. According to Takhtajan' s (1978) regionalization of the world flora, Kengyilia is distributed in the Eastern Asiatic Region and the Irano-Turanian Region of the Holarctic Kingdom. Six species occur in the Eastern Asiatic Region where endemic species are ab- sent. In the Irano-Turanian Region there exist 26 species and 6 varieties, 26 of which are endemic taxa, and in this region the highest concentration of the taxa occurs in Tibet Province, with 19 spe- cies and 6 varieties. In China, according to Wu' s(1979) regionalization of the Chinese flora, Kengyilia is found in 4 regions. Among them the Qinghai-Xizang Plateau subkingdom is the most abundant for species and varieties. The area totally has 16 species and 6 varieties, taking up 68% of the total taxa of Kengyilia and 75% of all taxa of Chinese Kengyilia, and these taxa include the primitive to the most advanced ones in the genus. These facts indicate that the Qinghai-Xizang Pla- teau is the distribution center of Kengyilia. The primitive section in Kengyilia is sect. Kengyilia, consisting of 9 species. It is highly centred in the Tianshan area where 5 species occur, of which K. zhaosuensis is the most primitive species in the genus. The relatively primitive section of the ge- nus is sect. Stenachyra L. B. Cai which contains 10 species and 3 varieties. Two of its species also grow in Tianshan area. In Tianshan area, on the contrary, there is not the sect. Hyalolepis (Nevs- ki) L. B. Cai which is considered as the most advanced section in the genus. Based on our study and relevant references, the closely related group of Kengyilia is the genus Roegneria C. Koch. Some species of Roegneria is not only distributed in Tianshan area, but also their habitats in the ar- ea agree with that of primitive species of Kengyilia. Moreover, since Tianshan Mountains were raised once more in the Neogene, the area had possessed the natural conditions to produce and mul- tiply Kengyilia plants. Hence, this area is likely to be the origin place of Kengyilia. Before the Mesozoic, the ocean and land in Tianshan area changed greatly. Being a xerophytic genus, Kengy- ilia could not live in the environment of waters. From the Mesozoic to the end of the early Tertiary of Cenozoic, the crustal movement in Tianshan area was tending toward tranquility. Owing to the denu- dation, the original high mountains were leveled forming the primary plain. The landforms and en- vironment in Tianshan area resembled those