PHYTOGEOGRAPHIC SIGNIFICANCE OF THE EOCENE FLORA OF HORSEFLY RIVER, BRITISH COLUMBIA

About thirty genera, including a few ferns, gymnosperms, and many angiosperms based on impressions of leaves, fruits and seeds, are known from Early to Middle Eocene lacustrine shales of Horsefly River, British Columbia, Canada. The Horsefly River flora shows similarities to Early and Middle Eocene floras of eastern Asia as well as to Early and Middle Eocene floras of mid-continental North America. Ginkgo, Metasequoia, Pinus, Koelreuteria, Nyssidium, Ulmus, and Deviacer are shared with the Eocene of Northeastern China. Fagopsis, an extinct genus best known from the Late Eocene of Florissant, Colorado, is represented by both fruits and leaves from Horsefly River. Macginitiea is seen here at its most northerly occurrence in North America. Dipteronia, Palaeocarpinus, Florissantia, Sassafras, and an extinct fruit type with paired, apically extended wings, are among the taxa shared with other western North American Eocene floras. These comparisons demonstrate probable floristic exchange between northwestern North America and Northeastern China during the Early and/or Middle Eocene. In contrast, the Horsefly River flora shows very little generic similarity to Early and Middle Eocene floras of Europe. Farther to the south, the Clarno Formation of Oregon includes elements shared with European Eocene floras as well as with the Horsefly River and Chinese assemblages.