Vine Weeds of Missouri - Page 13
Poison ivy has a reputation for dermatitis. When poison ivy grows as a vine, it attaches itself to objects using its aerial roots. It may also grow as a single plant and form thickets. It propagates by several means, including seed, extensive rootstocks and the stems that are capable of rooting where contacting the soil surface.
For identification, the key feature is its leaves. The leaflets are always in a group of three, trifoliolates. The two lateral leaflets often develop a lobe along their margins, which gives them a “mitt” shape. The petioles that support the lateral leaflets are shorter than the petiole of the terminal leaflet. Poison ivy leaves lack hairs. Stems and leaf veins of young plants often have a reddish color. The flowers are inconspicuous, as they are greenish in color. Its berries are whitish gray and may persist along with the plant's woody stems during winter months.
Poison oak, a related species, is sometimes confused with poison ivy; however, it is not nearly as widespread. In Missouri, poison oak is only found in scattered southern counties.
Some also confuse Virginia creeper with poison ivy; however, it has five leaflets rather than three.