Morphological features of sumac leaves (Rhus, anacardiaceae), from the latest early eocene flora of republic, washington

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International Journal of Plant Sciences


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 mor-phology, 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 today. Conclusions. This study demonstrates greater systematic diversity than previously known within the genus Rhus in the Okanogan Highlands flora of Republic, Washington. These leaves also provide additional evidence for possible hybridization and other evolutionary processes at play within the sumacs by the latest early Eocene in western North America.


Biological and Environmental Sciences

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