Eastern Asian-Eastern North American Phytogeographical Relationships-A History From the Time of Linnaeus to the Twentieth Century

Abstract

The awareness and study of eastern North American-eastern Asian plant disjunctions is traced from the time of Linnaeus to the beginning of the twentieth century. Thomas Nuttall's previously overlooked contribution to this topic is discussed, and an annotated appendix of the taxa that he attributed to eastern Asia and North America is presented. Charles Darwin's influence on the thoughts and writings of Asa Gray is also discussed, based on published and unpublished letters and manuscripts in the Archives of the Gray Herbarium of Harvard University; the role that this correspondence played in the development of Gray's phytogeographical ideas and Darwin's theory of evolution is considered. A brief summary of the writings of Adolf Engler, and other nineteenth century botanists, pertaining to these disjunctions and their bearing on an understanding of vegetational patterns in the northern hemisphere is also given. The significance of the late nineteenth century explorations in China in making known the full extent of disjunctions between eastern Asia and North America has provided the basis for further work beyond the exploratory and theoretical stages of this fascinating pattern of plant disjunction. The discontinuous distribution of the same or closely related taxa of plants between eastern North America and eastern Asia is but one of several patterns of disjunction that become evident when the flora of the temperate Northern Hemisphere is considered (Raven, 1972; Thorne, 1972; Wood, 1972; and others). Many of these patterns have been termed Tertiary relict disjunctions. Of these, however, the classic eastern North American-eastern Asian pattern is undoubtedly the best known and most often cited example of the disjunct occurrence of closely related taxa on two continents separated by thousands of kilometers. Despite the fact that most of the shared taxa in the two regions have been shown to be distinct from one another (the relationships are primarily closely related species of the same genus, or closely related genera of the same family), other factors noted by biogeographers that have strengthened the impression of a biological connection between the two regions are climatic and ecological similarities. The similarities of the forests of Japan, central China, and the southern Appalachians in appearance as well as in ecological associations are in many instances so great that a sense of deja vu is experienced by botanists of one of the regions visiting the other. Another important factor that has served to emphasize the floristic relationships between eastern North America and eastern Asia is the fact that this particular disjunction pattern was the first to be recognized by botanists. Moreover, the discovery and significance of this pattern figured in the discussions surrounding Darwin's theory of evolution, and it has been discussed not only by plant geographers but by botanical and scientific historians as well. The purpose of this paper is to trace briefly the historical aspects of the recognition of this distribution pattern and the accumulation of facts pertaining to it, and to summarize the major contributions to the study of this pattern that have been made from the time of Linnaeus to the beginning of the twentieth century. Special mention of the contribution and observations of Thomas Nuttall is inI We thank M. Byrnes for her help in the preparation of the manuscript, 0. T. Solbrig, Director of the Gray Herbarium, for allowing access to the Darwin and Gray material in the Archives of the Gray Herbarium, and L. McWood, Archivist, for her patience and helpfulness. We also thank D. Kohn, B. G. Schubert, and P. F. Stevens for reading the manuscript and for their comments, and P. H. Raven, who suggested that we attempt this contribution. Lastly, we are grateful to B. Bartholomew and the library of the California Academy of Sciences for providing a copy of Miquel's paper of 1868, and to P. H. Raven and the Missouri Botanical Garden for providing copies of other literature that we were lacking. 2 Harvard University Herbaria, 22 Divinity Avenue, Cambridge, Massachusetts 02138. ANN. MISSOURI BOT. GARD. 70: 423-439. 1983. This content downloaded from 157.55.39.58 on Fri, 24 Jun 2016 04:59:20 UTC All use subject to http://about.jstor.org/terms 424 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 70 cluded inasmuch as his penetrating insights into the relationships between the eastern Asian and eastern North American floras, as well as his phytogeographical observations, have to our knowledge hitherto passed unnoticed. EARLY RECOGNITION OF THE FLORISTIC SIMILARITIES BETWEEN EASTERN NORTH AMERICA AND EASTERN ASIA-