ZIZYPHOIDES LEAVES FROM THE LATEST EARLY EOCENE REPUBLIC FLORA OF NORTHEASTERN WASHINGTON STATE, USA

The latest early Eocene Republic flora of northeastern Washington State is a highly diverse megafossil assemblage that is among the oldest warm temperate floras in the Northern Hemisphere Paleogene. Republic includes extant genera of endemic Asian affinities such as Trochodendron and Tetracentron (Trochodendrales), as well as two extinct genera also thought to belong to Trochodendrales, the fruit Nordenskioldia and its associated leaf Zizyphoides. While Nordenskioldia is rare at Republic, Zizyphoides is fairly abundant and is distinct from both the Paleocene species Z. flabellum and the Miocene Z. auriculata. Reconstructions of the Nordenskioidia/Zizyphoides plants of Paleocene and Miocene ages typically include a long-shoot, short-shoot system similar to that of extant Cercidophyllum (Cercidiphyllaceae), a plant which has often been linked to the Trochodendrales. Cercidiphyllum has a predictable pattern of arrangement of its polymorphic leaves, with reniform leaves borne on short shoots, elliptical leaves on long shoots, and underdeveloped reniform types. Examination of Zizyphoides flabellum from the Paleocene of North Dakota shows this same pattern of variation, as does the Republic Zizyphoides. Likewise, the distribution of glands in Zizyphoides is comparable to what would be expected in a long-shoot, short-shoot morphology. In describing leaf types from Zizyphoides and Cercidophyllum-like taxa, we propose recognizing types within the diagnoses to clearly reflect the nature of variation present within individuals.