 All members of the genus produce the skin-irritating oil urushiol, which can cause a severe allergic reaction.The generic name is derived from the Greek words τοξικός ("toxikos"), meaning "poison," and δένδρον ("dendron"), meaning "tree".The best known members of the genus in North America are poison ivy "(T. radicans)", practically ubiquitous throughout most of eastern North America, and western poison oak ("T. diversilobum"), similarly ubiquitous throughout much of the western part of the continent.