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Rhus radicans L.—Poison ivy

FAMILY: Anacardiaceae—the Cashew Family

Many readers will be surprised to learn that the edible cashew nut belongs to the same family of plants as poison ivy and poison sumac. This predominantly tropical family has leaves: alternate, compound; flowers: 5-merous, polypetalous, regular, with an annular disc between the 5 stamens and ovary; ovary: 1-celled, containing I ovule; fruit: a drupe.

PHENOLOGY: Poison ivy produces inconspicuous greenish flowers from May through July.

DISTRIBUTION: Rhus radicans is commonly found in disturbed habitats, food plains, cultivated fields, cemeteries, waste places, along woodland paths, margins of woodlots, fencerows, roadbanks, along streams, and in urban situations around buildings and yards.

PLANT CHARACTERISTICS: The species has complex and variable forms. Some are woody vines that produce aerial roots and grow by straggling and climbing over other vegetation. Ground-forms usually spread by rhizomes and develop dense colonies with a few leaves crowded near the summit. Regardless of growth habit, poison ivy always has three leaflets per leaf, with leaflets: ovate to subrotund, varying to rhombic or elliptic, terminally acute to acuminate, basally cuneate; entire to irregularly serrate or crenate; glabrous or thinly pubescent, petiolule of the terminal leaflet longer than those of the lateral leaflets; panicles: axillary, 1 dm long, bearing greenish-yellow flowers that mature into grayish white fruits, 5-6 mm; fruits: mature August through November, conspicuous all winter; birds eat the ripe seeds with impunity.

POISONOUS PARTS: All parts of poison ivy, with the possible exception of the pollen, contain toxins that cause dermatitis. It has been suggested that extremely sensitive persons might contract poison from wind-blown pollen in spring when the plant is flowering.

SYMPTOMS: Dermatitis ranging from minor reddened and itching skin to major swelling, blisters, and weeping wounds can result from contact. Ingestion of leaves can cause irritation of the mucosa and digestive tract; gastritis and death may result. Animals probably are not as susceptible as humans to contact dermatitis due to hair and fur. Ingestion of leaves or other plant parts by livestock could be dangerous and result in death.

POISONOUS PRINCIPLES: The toxin 3-n-pentadecylcatechol has been isolated from Rhusradicans.

CONFUSED TAXA: The plant most commonly confused with poison ivy is Virginia creeper, Parthenocissus quinquefolia, which produces berries that are poisonous upon ingestion (see Parthenocussus). A reliable feature useful in differentiating the two plants is the compound leaf Virginia creeper has 5 leaflets, whereas poison ivy has 3 leaflets per leaf. Ash tree species in the genus Fraxinus, and boxelder (Acer Negundo L ). can superficially resemble poison ivy, especially as seedlings; however, the former two have opposite leaves, whereas poison ivy has alternate leaves.

SPECIES OF ANIMALS AFFECTED: Contact dermatitis is commonly seen in humans. Fifty percent of the population is allergic in some degree to poison ivy. Consumption of this plant will affect humans, and probably livestock as well.

TREATMENT: For dermatitis: (4); (23); in severe cases steroid injections can reduce the reaction.

OF INTEREST: The following concerning poison ivy are true. They are listed to dispel popular myths.

  • Poison oak is not found in Pennsylvania.

  • Poison ivy plants contain the skin irritant all year.

  • The plant must be bruised or broken for the toxin to exude from the plant; there is no substantial evidence for the plant otherwise exuding the poisonous principles.

  • The toxin is not volatile nor air borne except when carried in droplet form on smoke, dust, or combusted particles generated by burning the plant.

  • Weeping wounds and blisters do not spread poison ivy over the body.

  • Towels or clothing contaminated by the serum from weeping wounds will not spread the itching.

  • New blisters are the result of delayed response at the site of infection, renewed contact with the plant, or recontact with irritant-contaminated articles.

  • The irritating chemical can be spread from contaminated articles, clothing, pets, garden tools, etc.

  • After contact with the irritant, symptoms may appear within hours or up to a week later.

  • Poison ivy plants can be eliminated by herbicide application. These compounds are generally nonselective and may kill surrounding vegetation if applied improperly.

  • For a list of currently registered herbicides contact the Pennsylvania Department of Agriculture, the County Agricultural Extension Office, a local lawn and garden center, or agricultural farm products supplier.


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