试论我国沙漠地区植物区系的发生与形成

A STUDY ON ORIGIN AND FORMATION OF THE CHINESE DESERT FLORAS

本文对前人的“关于我国沙漠地区的植物区系的发生和形成”的不同观点进行了概括,并着重对我国沙漠地区起主导作用的古地中海、中亚及蒙古区系成分中有影响的植物属种及其迁移途径进行了分析。我国沙区大部在老第三纪已形成了亚热带旱生植物。但由于地域辽阔,其形成既非统一的古老性,也不全年轻,而是因地而异。本文根据(1)地理位置、地形、受古地中海海浸海退、冰川的消长、高山的屏障作用、距海洋的远近以及印度板块的影响,(2)区系成分中的特有属种、寡种属、特征种、间断分布等,将我国沙区分为准噶尔盆地、塔里木盆地、柴达木盆地、阿拉善荒漠、东部草原区沙地五片,并讨论了其区系成分的来源及形成时期。准噶尔植物区系在第四纪形成,中亚成分占主导作用。塔里木盆地植物区系在老第三纪就已发生,第三纪形成,第四纪有新发展。柴达木盆地在新第三纪上新世已形成温带荒漠,第四纪有新发展。阿拉善荒漠植物区系在第三纪已形成,第四纪也有新发展。东部草原区沙地第四纪在几个中心同时发生,其成分包括蒙古、亚洲中部、东亚、华北等区系。

This paper summarized the different views of former authors about the origin and formation of the Chinese desert floras. Some authors considered that the Chinese desert floras formed with mixed elements of other floras during the Quarternary period because there were very few endemic genera and species in it. Others held that northwestern China had already been a continent since the Late Paleozoic era and the aridity had been enhanced especially during the Tertiary period, which indicates the ancientness of the Origin of the Chinese deserts. Besides, the presence of many monotypic and oligotypic genera in the desert flora can also explain it. There are also some authors, who thought that plants in Chinese desert flora are mostly descendants of the xerophytes of the Tethys, and thus the common species between northeastern China and Middle Asia reflect a more ancient relationship, while others considered that those common species reflect a more recent relationsip. For tracing back to the formation of the Chinese desert floras, an analysis of some geographical elements that played a leading role in it is made. 1. Geographyical elements of the Tethys. In the genus Gymnocarpos G. decander is distributed along the Mediterranean coast, and G. przewalskii is distributed in Xinjiang, Gansu, Qinghai, Ningxia and Inner Mongolia in China. In the genus Cornulaca C. monacantha is distributed in Africa and C. alaschanica in the Alashan area, while in the genus Cynomarium C. coccineum is distributed in Sahara and C. songaricum in the sandy areas in China. These disjunctions reflect a more ancient relationship between floras of the Chinese sandy areas and the Tethys. There are five species in Frankenia in Africa, while only one species, E. pulverulenta, occurs from northern Africa to Xinjiang and Gausu via Middle Asia. In the genus Helianthe- mum there are eight species along the Mediterranean coast, while in Middle Asia and in western China there is only one species, H. songarium. At present many Mediterranean species are still present along the Tethys tracks, some of which stop in Xinjiang, e. g. Atriplex dimorphostegia; some stop in Hexi, Gansu, e. g. Capparis spinosa; some go deep into Ningxia, e. g. Peganum harmala and some extend eastwards even to the Middle Inner Mongolia, e. g. Populus euphratica. All these facts prove that weastern China joined together with the Tethys. After great changes had taken place in the earth history, disjunction occurred in some plant species-some became degraded and extinct, while others preserved. 2. Floristic elements of Middle Asia. The formation of plant genera in the Middle Asian flora is related to the Tethys flora and they further differentiated. The Middle Asian flora is closely related to those of our sandy areas. For example in the large genus Salsola, 22 species are distributed in Junggar of China and 59 in Middle Asia of the former USSR, while 25 are shared by the two floras. In the genus Zygophyllum 17 species are shared by the Middle Asian flora with 38 species of this genus and the Chinese flora with 16 species distributed in Junggar. Thus, a common trend can be recognized that the Middle Asian species are in common mostly with those in the Junggarn flora, and the more eastward, the fewer the common species are present. In the Middle Asian florra there exist many species of ephemeral plants and ephemeroides, but in the Chinese desert flora forty odd such plant species are distributed only in Junggar and mostly in common with those in the Middle Asian flora e. g. Euphorbia turzanincrwii, Gagea bulbifera. In sandy areas of Middle Asia Haloxylon ammodendron and H. persicum are two of ed-ificators, of which the former has its distribution in our desert areas, but the latter is distributed in the Junggar Basin only. The Middle Asian flora exerts its strongest influence on those of our sandy areas and the Junggarn flora is a part of the Middle Asian flora. 3. Floristic elements of Mongolia. In the Chinese sandy areas all the floras belong to the Mongolian floras except tho