Fossil Corylopsis and Fothergilla leaves (Hamamelidaceae) from the lower Eocene flora of Republic, Washington, U.S.A., and their evolutionary and biogeographic significance

Corylopsis reedae Radtke, Pigg et Wehr sp. nov. and Fothergilla malloryi Radtke, Pigg et Wehr sp. nov. (Hamamelidaceae) are described from the lower Eocene (49-50 million years ago) Republic flora of northeastern Washington State. Corylopsis reedae is the first unequivocal fossil leaf report of Corylopsis Siebold & Zucc. (cv. Winter Hazel). The species is based on a single specimen that is 1.9 cm wide, preserved for 3.4 cm in length and estimated to be ca. 4 cm long, with an asymmetrical base and teeth that are concave apical, straight basal, with simple apices. The fossil leaf is remarkably similar to extant Corylopsis, with prominent compound agrophic veins; strong, straight secondaries; and closely spaced, ladder-rung-like, opposite to alternate percurrent tertiaries at right angles to the secondaries. Today this genus occurs only in Asia, but the fossil record, primarily of seeds, indicates it was widely distributed in North America and Europe during the Tertiary. Fothergilla malloryi documents conclusively the presence of this genus in the lower Eocene of North America for the first time. This leaf is 4.4 cm long x 3.5 cm wide and slightly lobate, with low, widely spaced teeth on the margin, an asymmetric apex, and a cordate base. This occurrence represents the oldest record for the genus, which is also known in the Oligocene of North America and several Neogene Asian localities. Today, Fothergilla (cv. Witch Alder) is native to southeastern North America. The occurrence at Republic of these two hamamelid plants underscores the diversity of the northwestern "Okanogan Highlands" flora of British Columbia, Canada, and Washington State, and demonstrates the Early Eocene presence of two disjunct hamamelid genera. These occurrences provide new data for better understanding the evolution and biogeography of the family.