以礼草属的地理分布

Geographical distribution of Kengyilia Yen et J. L. Yang(Poaceae)

根据植物类群的地理分布与系统发育相统一的原理 ,本文讨论了以礼草属的分布中心、起源地、起源时间和现代分布格局的形成。以礼草属全世界约 2 6种、6变种 ,隶属于 3个组 ,主要分布于中国 ,哈萨克斯坦、吉尔吉斯斯坦、塔吉克斯坦、阿富汗和伊朗也有分布。其中 ,中国的青藏高原汇聚了该属的大多数种类 ,且不同等级和演化水平的类群均集居于此 ,使其成为该属的现代分布中心 ;而该属的原始类群、以及与原始类群很近缘的鹅观草属却分布在这一中心之外的天山地区 ,加之天山地区自新生代的晚第三纪再次抬升以来 ,具备了以礼草属发生和繁衍的自然条件 ,因而天山地区很可能就是该属的起源地 ,起源时间也可能在晚第三纪或第四纪初。以礼草属自天山起源后 ,扩散的途径大概有 3条 ,其中西南向途径和东南向途径从东、西两侧侵入青藏高原 ,在青藏高原得到极度发展 ,并随着高原的继续隆起 ,进一步衍生出最高级的类群短穗组 ,从而形成了以礼草属现今的分布格局。

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 sections, 26 species and 6 varieties in Poaceae. The genus is distributed in China, Kazakhstan, Kirghizia, 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 absent. 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 species 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 Plateau 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 genus 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 (Nevski) 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 area 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 multiply 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, Kengyilia 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 denudation, the original high mountains were leveled forming the primary plain. The landforms and environment in Tianshan area resembled those of its adjacent areas. Consequently, it was still unlikely to cause the birth of Kengyilia. Only in the Neogene of Cenozoic and even in the early period of the Quaternary, the primary plain in Tianshan area began to rise rapidly. The tremendous changes of landforms and environment had taken place in the area. In the course of adapting to this change, the ancestor of Kengyilia produced probably the plant of the genus during this time. Besides, before the end of the early Tertiary, the climate in Tianshan area belonged to the subtropic type. The damp and hot climate was unfavourable to the birth of Kengyila which possesses the temperate characteristics; while only from the end of the early Tertiary, up to the end of the Neogene, the climate in the area was gradually getting into aridity and coolness, suitable for the existence and multiplication of Kengyilia plants. In addition, the origin time of Kengyilia fits in with the origin of its closely related genus and the fossil record of Poaceae. After Kengyilia originated from the Tianshan area, besides development and differentiation, it disperse