Rhus
Collier's New Encyclopedia (1921)
in botany, a genus of Anacardiaceæ. Leaves simple or compound. Flowers in axillary or terminal panicles, bisexual or polygamous. Calyx small, persistent, five-partite; petals five: stamens five; ovary one-celled, sessile; fruit a dry drupe, with one exalbuminous seed. Nearly 100 species are known. Most are shrubs, from 6 to 10 feet high. They exist in all the continents. The leaves of R. coriaria, the hide or elmleaved sumach of the S. of Europe, are used for tanning morocco leather. In the Himalayas those of R. cotinus are similarly employed. The fruit of the former was given in dysentery. In India, R. parviflora, R. semialata, R. succedanea, are used medicinally. Exudations from incisions in the bark of R. succedanea and R. vernicifera yield the varnish used in Japanese and Chinese wickerwork. The former produces astringent galls, and its seeds yield a kind of wax; as do also those of R. wallichii and the Japanese R. vernix. The juice of the latter species blisters the skin. The Turks used the acid fruits of R. coriaria to sharpen their vinegar. The plant yields sumach. The bark of R. glabrum is a febrifuge, and is employed as a mordant for red colors. R. metopium, a Jamaica plant, yields a medicinal gum. R. toxicodendron (used in pharmacy as a topical irritant) and R. venenata, American species, are poisonous, nor is any of the genus very safe. These two species are called indifferently poison oak, poison ivy, poison sumac, and more rarely mercury. The wood of R. collinus is employed for inlaid and cabinet work.
What Has Changed in the Last Century
The genus Collier's described in 1921 has since been broken up. The poisonous species it lists "indifferently" as poison oak, poison ivy and poison sumac — R. toxicodendron and R. venenata — together with the Japanese lacquer tree R. vernicifera, are now placed in a separate genus, Toxicodendron (poison ivy is Toxicodendron radicans, the lacquer tree T. vernicifluum), while R. cotinus, the smoke tree, is treated as Cotinus coggygria. The blistering agent is known to be urushiol, an oily catechol mixture named from the Japanese urushi for lacquer, and it causes a delayed allergic contact dermatitis rather than a simple chemical burn; sensitivity varies from person to person, which is why some people handle the plants with impunity. Collier's warning that "nor is any of the genus very safe" no longer holds for Rhus proper: staghorn sumac fruits are made into a drink, and the ground fruit of R. coriaria is a common Middle Eastern spice sold as sumac.
Written for this edition, 2026.