Western poison-ivy is of interest chiefly because of its irritating 

 effect on the human skin. Although some persons are little affected 

 by western poison-ivy few, if any, are entirely immune. Lower 

 animals apparently do not react to the poison; in fact, livestock 

 which crop the plant experience no ill effects. In the past, some of 

 the most conservative botanists have classified this species merely as 

 a western, nonclimbing form of the common poison-ivy (T. radicans, 

 syn. R. rod icons] of the East. However, the geographical distribu- 

 tion of these two species is distinct, and there are well-marked char- 

 acters of leaves, flowers, and fruit which differentiate them. West- 

 ern poison-ivy occurs from South Dakota to western Oklahoma. 

 Arizona, Oregon, and British Columbia, growing in a wide variety 

 of situations from, the foothills to the ponderosa pine belt, and often 

 being abundant in thickets along streams, in canyons, and on dry, 

 rocky hillsides. Although occasionally nibbled by livestock it is 

 negligible or poor as a browse plant. 



It is risky to handle this species, or any members of the genus in 

 studying botanical characters, unless proper precautions are taken 

 to avert poisoning. Fortunately, western poison-ivy is recognizable 

 at a glance, being a relatively low, woody-stemmed plant with long- 

 stalked leaves divided into three, bright green, veiny, rather large, 

 coarse-toothed leaflets. The leaves turn a brilliant red in autumn, 

 and fall from the plants, but the clusters of whitish, shiny, berrylike 

 fruits usually remain attached to the stems throughout the winter. 

 The poisonous properties of this plant are practically the same as 

 those of other species of Toxicodendron and are treated in greater 

 detail in the accompanying discussion of the genus. 



POISON-IVIES, POISON-OAKS, AND POISON-SUMACS 



Toxicoden'dron spp., syn. Rhu's spp. in part 



Toxicodendron is a genus of small trees, shrubs, or climbing vines 

 having divided (trifoliolately or pinnately compound) leaves and 

 resinous sap; there are approximately 20 species native to North 

 America and Asia, with five occurring in the United States. The 

 more conservative botanists prefer to classify these plants with the 

 true sumacs (Rhus spp.). However, the group of species under 

 Tocfficodendron, whether given generic or sectional rank, has well- 

 marked characters, including a poisonous juice ; drooping, loose, and 

 axillary (instead of erect, dense, and terminal) flower clusters; a 

 single and unbranched (instead of three-branched) stalk (style) of 

 the female floral organ (pistil) ; and white or grayish, wax-produc- 

 ing, smooth or slightly fuzzy, usually shiny (instead of red or red- 

 dish, and densely pubescent) fruits, with ridged (instead of smooth) 

 stones. The generic name is a combination of the Greek toxicon 

 (pertaining to the bow) 2 and dendron (tree), meaning poison tree. 



The species of poison-ivy are not, of course, true ivies, i. e., ever- 

 green woody vines or climbing shrubs of the genus Hedera of the 



a It is worthy of note that the original poisons of mankind were arrow poisons, used in 

 obtaining food. This explains why our modern science of poisons (toxicology) gets its 

 name from a root word meaning bow. The Greeks used the phrase toxicon pharmakon 

 (literally "bow drug") for arrow poisons, and the later Latin word toxicum (poison) 

 appears to have been a sort of shorthand derivative from that phase. 



