If you've ever been victimized by poison ivy this will be of little comfort, but the plant isn't all bad. The sap, which turns black on exposure to air, used to be one of the only sources of that color before the introduction of synthetic dyes. Medically, the plant was used at one time to treat eczema and shingles, and some California-based Native American tribes used it to cure ringworm. History aside, the flora is best avoided and to do that, you must be able to recognize it amidst all the other woodlands greenery. While the leaves of plants in this genus (Toxicodendron) may be smooth-edged, sawtooth-edged, or lobed, they almost always grow in threes, with the middle leaf extending farther than the other two. The urushiol oil is devastating throughout the year, so beware of stems and vines in winter, and watch out for the leaves that turn red and yellow in autumn and blend in with oaks and maples. Oil can be carried by dust and ash particles in smoke when the plant is burned, so it's possible to get the itch after sitting around a campfire.