Toxicodendron radicans ssp. negundo

Native

Minnesota prohibited noxious weed

June to August

Woods, wood edges, wooded flood plains. Light shade to full sun.

Yellowish green

10″ to 36″

This is a climbing or trailing, perennial, woody vine that rises from a usually underground rhizome. It often forms colonies.

Stems are woody and produce abundant, centipede-like aerial roots that grasp the host tree.

Leaves are alternate on long, slender, densely hairy leaf stalks.

The leaves are divided into 3 leaflets. The leaflets may be egg-shaped, with the broad portion at the base where it attaches to the leaf stalk, or elliptic, broadest in the middle and tapering toward both ends. They taper to a point at the tip. They are 1″ to 6″ long. The two side leaflets are usually shorter than the central leaflet. The leaflet margins may have shallow lobes, they may have rounded teeth, or they may be entire. They tend to be flat, not folded along the midrib. Young leaves are reddish-purple, becoming somewhat shiny and greed with maturity. In the fall the leaves turn yellow, orange, or bright red.

Black spots may appear on any part of the plant. The spots are urushiol, the resin that causes allergic reactions. When the plant is damaged urushiol is exuded in an attempt to seal off the damaged area. The resin is creamy, turning brown-red then black with oxidation.

The inflorescence is a 3″ to 4″ long cluster with usually more than 25 flowers. The flower has 5 yellowish green petals.

The fruit is a smooth, dull white berry with a few gray stripes. The fruit cluster is stalked and hangs downward.

Western poison ivy (Toxicodendron rydbergii) is a shrub, not a vine. It does not climb trees. The stems do not have aerial roots. The leaf stalks are hairless. The leaflets tend to be folded slightly along the midrib, not flat. The inflorescence is 4″ to 16″ long. The fruit cluster is compact and erect.

Sources: 2, 3, 4, 5, 7, 8.

BONAP shows this species distributed throughout the state and occurring in most counties. All other sources show a much more restricted range. The map at left does not include the BONAP data.

Toxicity
Contact with the outer surface on an undamaged plant should not cause an allergic reaction unless there is residual urushiol present from a previous injury to the plant or a nearby plant. Contact with a torn leaf, broken or damaged stem or rhizome, or black spot will cause a reaction in those sensitized to urushiol. Several exposures to the substance may be necessary to impart sensitivity. Research has shown that 85% of all people will develop contact dermatitis after adequate exposure. It usually takes 12 to 48 hours for a rash to develop on a previously sensitized person. In some individuals, a single exposure will cause a reaction. In these individuals, the rash will develop in seven to ten days. The lesions last 14 to 20 days. Rashes do not spread and are not contagious. Treatment can dry the blisters, reduce swelling, and relieve itching, but will not speed healing.