The Sino-Japanese Floristic Region, comprising a notable and distinct assemblage of plants, ranges from the eastern Himalaya to Japan through the temperate and subtropical zones of China. Physiognomically the dominant vegetation comprises evergreen broadleaved forests, mixed evergreen-deciduous broadleaved forests (the dominant type) and deciduous broadleaved forests.

The flora has been considered to be homogeneous on the whole throughout and characterized by its richness in endemic families and endemic genera. However, our present knowledge of the flora and vegetation within the Sino-Japanese Floristic Region is still far from sufficient. To address this concern, and because of the widespread interest in this floristically distinct part of the world, a symposium on the Sino-Japanese Floristic Region was held during the Fifteenth International Botanical Congress in Yokohama in 1993.

The papers presented in the symposium provide a broad review of the floristic and vegetational details and aspects of the region. Because of interest in some of the papers presented in the poster sessions and their relevance to this topic, the contributors of those posters were also invited to prepare papers to appear in this issue.

The presence of many of the distinguishing families and genera of this floristic region, enumerated by Wu in this symposium, is clearly the result of favorable climates and habitats prevailing over long periods of time in at least portions of China and Japan. Many of the families and genera that now define this region, or are so characteristic of it, such as Cercidiphyllaceae, Ginkgoaceae, Metasequoia, Glyptostrobus, Cephalotaxus, Cathava, Cyclocarya, Pterocarya, Menispermum, Zelkova, Ailanthus and others have fossil histories that give evidence of their once widespread occurrence around the northern hemisphere. It should not be surprising, then, that the Sino-Japanese Floristic Region is also the Asian center of diversity for genera belonging to the classic Arcto-Tertiary pattern of disjunction between eastern Asia and North America and a few other localized parts of the world. The Asian distribution of many representatives of these Asian-American genera, such as Chamaecyparis, Tsuga, Torreya, Campsis, Buckleya, Caulophyllum, Diphylleia, Phryma, Penthorum, Pachysandra, Torreya, Carya, Saururus, Halesia, Stewartia, Cephalanthus, Amphicarpaea, Cladrastis, and numerous others, also help to define the Sino-Japanese floristic region. In a way, then, this region gives us a window, albeit a somewhat clouded one, on the more widespread forests of the past.

Among the basic needs in trying to understand the flora and vegetation of an area are the scholarly works, the checklists, floras and florulas, that enumerate the plants and provide the means of identifying and characterizing them. Floras and florulas are also critical for an understanding of a region's biodiversity and are important for studying an area's ecology and plant geography. A number of floras have been prepared for parts of China in recent years in addition to the monumental Flora Reipublicae Popularis Sinica, a treatment of all of China's plants that will eventually appear in 80 volumes and include about 120 books to treat the country's approximately 30,000 vascular plants. To meet the need for a basic reference to treatments of the plants of the Sino-Japanese Floristic Region, Ma and Gilbert have provided an invaluable account of the floras and florulas produced in China between 1949 and December 1996 for this volume.

Although the Sino-Japanese Floristic region includes large parts of both China and Japan, the floristic assemblages are not entirely uniform in the two areas. Two papers, one by Wang on the pteridophytes of Guizhou Province, China, and the second by Ying and Boufford on the flowering plants of the Qinling Mountain Range in east-central China, compare the floras of two particularly rich areas on the mainland with the flora of Japan. Of the 710 species of ferns in Guizhou, 40 percent are shared with Japan, which has 632 species of ferns. In the flowering plants, 63.8% of the 892 genera in the flora of the Qinling Mountains also occur in Japan; 39 genera are endemic to China. The distributional patterns of the species were analyzed and some comparisons were made with the flora of Japan. Of the approximately 3,125 species, endemic species and nonendemic species are nearly equally represented in the Qinling mountain range, and of the nonendemic species. 49.1% are shared with Japan.

The paper by Nooteboom shows the contributions to the Sino-Japanese Floristic Region of families more richly represented in other parts of the world, using the Apocynaceae as an example. Yet, even in the largely tropical Apocynaceae three interesting temperate genera within the Sino-Japanese Floristic Region are the American-Asian disjuncts Apocynum, Trachelospennum and Amsonia.

Ikeda and Ohba examine the distribution of several species of Potentilla between the Himalaya and the Sino-Japanese floristic region and speculate on the origin of some more recent patterns of distribution in Asia, and Miyamoto and Ohba discuss variation among closely related species of Eriocaulon. Cytology is used by Kurita and Hsu to elucidate cytological variation and patterns among hybrids in Lycoris, a genus endemic to the Sino-Japanese floristic region.

The discussion by Chen and Chen on the forests of China present a setting in which the forests of the Sino-Japanese Region can be viewed. And Xie's paper on the phytogeo graphical affinities in the forest floras of eastern China and Japan tend to focus more closely on similarities and differences between mainland and Japanese portions of this floristic region. Two additional papers, one by Li discussing the particularly rich vegetation of the upper Hongshui River region on the southwestern border of the Sino-Floristic Region and the other by Thin on the vegetation of Fansipan Mountain in Vietnam, outside of the Sino-Japanese region, make further comparisons with the flora and vegetation of other parts of the world.

The preliminary arrangements for this symposium and assistance to insure the participation of Asian botanists were made by the organization committee of the 15th International Botanical Congress and also by the Society of Himalayan Botany. The contribution of these organizations is gratefully acknowledged.