Qian Hong, Ricklefs Robert E
Am Nat. 1999 Aug;154(2):160-181. doi: 10.1086/303230.
Numbers of taxa at the level of order, family, genus, and species were tabulated for 12 subclass-level taxonomic groups of vascular plants in the floras of China and the United States. Analysis of these data showed that the flora of China is significantly more diverse than that of the United States. Furthermore, the difference in diversity arises at and below the level of genera. Finally, the euasterids II and Caryophyllidae are exceptions to the general trend in being more diverse in the United States. As a result, the floras of China and the United States are different nonrandom samples of the floras of the North Temperate Zone and the world. Phylogenetically older groups have a larger proportion of genera shared between China and the United States and also tend to have larger proportions of taxa belonging to genera with tropical affinities. The two subclass-level groups that are more diverse in the United States have primarily temperate affinities and are relatively young phylogenetically. We conclude that the patterns of diversity of Chinese and U.S. vascular plants have been influenced by the longer and more open access of temperate eastern Asia to tropical regions, the presence in southern China of a larger area of subtropical climate with complex topography, and the reduced impact of late Tertiary climate cooling in eastern Asia compared to North America. The greatest differences in diversity occur among older groups having stronger tropical affinities and, perhaps, originating in eastern Asia. In the North American flora, these groups appear to be disproportionately small relicts of a formerly widespread "boreotropical flora" that was relatively homogeneous at the genus level across the Bering Land Bridge between eastern Asia and North America. Groups that arose and diversified later, and that have fewer genera in common between Asian and North American floras, particularly the euasterids II, were better adapted to the cooler and drier climates of the Neogene temperate latitudes and evidently were relatively unaffected by late Neogene glaciations. These groups are thus as diverse, or more diverse, in North America as in eastern Asia. Understanding the relative diversity of two regions requires an appreciation of the historical development of the floras in the context of large-scale processes and events.
统计了中国和美国植物区系中12个维管植物亚纲分类群在目、科、属和种水平上的分类单元数量。对这些数据的分析表明，中国的植物区系比美国的植物区系多样性显著更高。此外，多样性差异出现在属及以下水平。最后，菊亚纲II和石竹亚纲是一般趋势的例外，它们在美国更为多样。因此，中国和美国的植物区系是北温带和世界植物区系的不同非随机样本。系统发育上较古老的类群在中国和美国之间共享的属比例更大，并且属于具有热带亲缘关系属的分类单元比例也往往更大。在美国更为多样的两个亚纲分类群主要具有温带亲缘关系，并且在系统发育上相对较年轻。我们得出结论，中国和美国维管植物的多样性模式受到以下因素的影响：东亚温带地区对热带地区更长时间和更开放的通道；中国南方存在更大面积的亚热带气候且地形复杂；与北美相比，东亚第三纪晚期气候变冷的影响较小。多样性的最大差异出现在具有较强热带亲缘关系且可能起源于东亚的较古老类群之间。在北美植物区系中，这些类群似乎是曾经广泛分布的“北热带植物区系”中不成比例的小残遗种，该植物区系在东亚和北美之间的白令陆桥上在属水平上相对同质。后来出现并多样化的类群，以及亚洲和北美植物区系中共有属较少的类群，特别是菊亚纲II，更适应新近纪温带纬度地区较凉爽和干燥的气候，并且显然相对未受新近纪晚期冰川作用的影响。因此，这些类群在北美与东亚一样多样，或更加多样。了解两个地区的相对多样性需要在大规模过程和事件的背景下认识植物区系的历史发展。
