Morphological Features of Sumac Leaves (Rhus, Anacardiaceae), from the Latest Early Eocene Flora of Republic, Washington

Premise of research. Newly identified fossils attributable to Rhus (Anacardiaceae) from the latest early Eocene flora of Republic, Washington, are recognized. Included are a revision of Rhus malloryi, three new species of Rhus based upon leaflet and rachis morphology, and a group of Rhus leaves showing variation in leaflet morphology, venation, and margin, in part comparable to similar features seen in hybrid angiosperms today. Together, these fossils demonstrate that Rhus was already undergoing diversification in western North America during the latest early Eocene.Methodology. Compression-impression fossils preserved in a lacustrine shale were uncovered from the rock matrix and photographed with light microscopy. Specimens were compared morphologically with fossil and extant material of related plants, and resulting images were processed minimally with Adobe Photoshop.Pivotal results. Fossil Rhus leaves are diverse in the Eocene and demonstrate morphologies characteristic of hybrid leaves in this genus ...