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To the Editor.—
It is of interest to review the antiquity of plants that cause dermatitis. A specimen of fossilized poison sumac leaves was obtained that was similar to current poison sumac (Figure). This was identified by paleobotanists as Rhus merrilli Chaney found in central Oregon in the John Day Formation. It is from the early Oligocene period. This makes it approximately 37.5 million years old. So, this plant was present long before any form of man appeared on earth. It is hoped that other members of the famed Anacardiaceae family, such as R toxicodendron and R diversiloba, will be found as fossilized and unchanged markers of skin contactants.
Goldman L. The Antiquity of Poisonous Plants. Arch Dermatol. 1979;115(12):1392. doi:10.1001/archderm.1979.04010120002003