BIOGEOGRAPHICALRELATIONSHIPS OF NORTHAMERICAN TERTIARYFLORAS'Steven R. Manchester2ABSTRACT Comparisons of Tertiary floras of North America with those of Europe and Asia document a long history of floristicinterchange. The stratigraphie and geographic ranges of selected conifer and angiosperm genera that are easily recog-nized in the fossil record provide a basis for discerning patterns in the routes and timings of intercontinental dispersaisthrough the Tertiary. The origin of the extant flora and vegetation ofNorth America has been the subject of much in-terest and debate ever since the floristic similaritiesbetween North America and Asia were first docu-mented. Many of the woody genera comprisingNorth America's present-day forests have excellentfossil records that can be traced through the Ter-tiary in North America and other continents of theNorthern Hemisphere (Wolfe, 1975; Graham, 1993;Tiffney, 1985a, b; Mai, 1995). In addition, manygenera that are no longer native to North Americahave well-documented Tertiary records. Patterns ofgeographic disjunction among extinct and extantgenera provide important clues to the history ofNorth American flora and the former continuity ofTertiary forests in the Northern Hemisphere. Bycomparing the stratigraphic records of generashared among two or more continents it is possibleto consider the pathways and timing of plant inter-change through the Tertiary. Many ideas have been published on the paleo-botanical origins and development of extant floraand vegetation of the Northern Hemisphere (e.g.,Engler, 1879; Chaney, 1940, 1947; Wolfe, 1975;Raven & Axelrod, 1974; Latham & Ricklefs, 1993;Mai, 1995; Akhmetiev, 1996). In the attempt to beas comprehensive as possible, investigators havesometimes relied uncritically upon genera reportedin the literature. Closer scrutiny reveals many er-roneous generic determinations (Dilcher, 1974).The purpose of this review is to highlight Tertiaryrecords of selected conifer and angiosperm generathat may be considered soundly identified andwhich are significant in understanding the biogeo-graphic affinities of North American Tertiary floras.I present a review of about 90 genera with reliableTertiary records in North America and other con-tinents. Examination of the stratigraphic ranges ofdifferent taxa in North America, Europe, and Asiaprovides the basis for assessing phytogeographicpatterns and pathways of biotic dispersai throughthe Tertiary. South American and African recordsare mentioned when known, but the emphasis is onaffinities within the Northern Hemisphere. For areview of relationships between North and SouthAmerica, see Burnham and Graham (1999, this is-sue). Because of our familiar vantage point of the pres-ent day, neobotanists and paleobotanists alike tendto regard the modern flora as an endpoint showingthe "true" floristic patterns of extant genera andspecies. Thus a genus such as Ginkgo, with a widepaleogeographic distribution (Tralau, 1968), may beclassified as an "East Asian element." Clearly, such"elements" have more to do with extinctions else-where than they do to the natural geographic affin-ity or origin of the genus (Wolfe, 1975). Fossils candocument former geographic distribution patternsof both extinct and extant genera and thus providea means of tracking the changing floristic relation-' 1 thank M. A. Akhmetiev, D. E. Boufford, Z.-D. Chen, M. Collinson, D. L. Dilcher, B.-Y. Geng, L. B. Golovneva,L. J. Hickey, L. Klise, Z. Kvacek, R. Serbet, B. Tiffney, K. Uemura, W. Wehr, J. Wen, and V. Wilde for data and advicehelpful in the preparation of this report. Hongshan Wang helped with translation of Chinese literature. The manuscriptalso benefitted from critical reviews by R. Stockey, B. Tiffney, and Z. Kvacek, and editing by P. Crane, A. McPherson,and V. Hollowell. I thank Patrick Herendeen and Peter Crane for inviting me to participate in the symposium thatbrought about this volume. This research was supported in part by grants EAR 9506727 and INT 9722444 from theNational Science Foundation and represents no. 499 in the Contributions to Paleobiology from the Florida Museum ofNatural History. ' Florida Museum of Natural History, Gainesville, Florida 32611, U.S.A.ANN. MISSOURI BOT. GARD. 86: 472-522. 1999.
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