中国与北美苔藓植物区系关系的探讨

关于中国和北美间苔藓植物区系关系的研究是在20世纪90年代开始的。研究表明中国和北美苔类和藓类的种间关系疏远，这一事实说明两个大陆在第三纪后期分离后，由于地质、地理、气候等因素的差异致使苔藓植物区系成分也产生明显分异。虽然它们在科、属方面差异较小，但两个大陆已各自形成地区特有的苔类和藓类的属。已知的中国特有及东亚特有的苔类属有5个，藓类属有22个；而已知北美地区特有的苔类属有4个、藓类属有5个。北美东部和西部形成于不同地质时期，在苔藓植物方面与中国共同分布的科、属和种存在一定差异。从神农架藓类植物研究表明，从共同分布的种来看，北美东部与中国比北美西部与中国的相似性系数高约6％。从两地区间苔类和藓类植物的雌雄同株或雌雄异株及孢子直径大小而论，这两个因素似乎并不是影响苔藓植物在两大地区间分布的主要原因，但对苔藓植物的分布仍然十分重要。本文作者认为结合中国和北美的地史、地理条件及苔藓植物自身的特点，可以认为白令海峡不是阻碍中国和北美苔藓植物交流的绝对自然屏障；中国和北美苔藓植物区系关系目前的状况，是长期多次交流融合和分异的结果。

Phytogeographical relationships of the bryophytes between China and North America

In this paper, we analysed in detail both hepatic flora and moss flora of China and North America to have a better understanding of the bryological relationships between these two continents. The results show that the similarity coefficient of the bryophytes between China and North America is very high (up to 88.03%) at the family level, but very low (only 18.88%) at the species level. Although the separation of the two ancient continents started in the late Cretaceous, the bryophytes between China and North America with respect to the composition of families and genera are still close. Nevertheless both continents have had their own endemic genera of liverworts and mosses. There are five East Asiatic endemic genera of liverworts and 22 East Asiatic endemic genera of mosses in China, while there are four liverwort genera and five moss genera endemic to North America. It is noteworthy that the bryological relationships between eastern North America and China show a quite different pattern from those between western North America and China with respect to the families, genera and species. The sexuality of plants and the size of spores of liverworts and mosses may not be the main factors that have influenced the distribution of the bryophytes in China and North America, although they are of some importance for the distribution of bryophytes. Various information concerning the bryological relationships between China and North America (including the similarity coefficients of the bryophytes of China and North America at different levels, their endemic genera, the sibling species of the two continents, the geological history and physical geograhical conditions of China and North America, and the biological characters of bryophytes) has been analysed. It is considered that there exist close bryological relationships between China and North America, although in these two separated continents some local and endemic genera had been formed after the Cretaceous. Both bryofloras have been influenced by those of their neighbouring regions, and the Bering Strait may not be a natural barrier to prevent the bryological exchange between China and North America. In summary, the present relationships of the bryofloras between China and North America have been formed not under the influence of one simple facter or event but under a comprehensive influence of many factors or events during the geological history.