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Poison Ivy, Poison Oak, and Poison Sumac - biology.

Publié le 11/05/2013

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Poison Ivy, Poison Oak, and Poison Sumac - biology. Poison Ivy, Poison Oak, and Poison Sumac, common names applied to three plants of a genus in the cashew family, capable of producing an allergic reaction in people who have become sensitized to them. Poison ivy and poison oak are variants of a single plant (sometimes treated as separate species by botanists), different mainly in the shape of their leaflets. Both are woody perennial plants of roadsides, thickets, hedgerows, and open woods, and one or the other is found throughout the United States and southern Canada. They may take the form of vines climbing up tree trunks to considerable height, shrubs or subshrubs standing erect by themselves, or vines trailing on the forest floor, sometimes also trailing out into meadows from hedgerows. Distinguishing characteristics include the regular grouping of three leaflets in each leaf, and stiff clusters of small, yellowish or white berries that appear in summer and fall. Other characteristics vary considerably, especially size of leaflet, notching, whether the surface is shiny or dull, or color. Poison sumac is a tall, smooth-stemmed shrub that grows in swamps throughout the eastern United States and Canada. It bears pinnately compound leaves with about 7 to 13 leaflets, including one at the tip. The fruits are white or yellowish berries in clusters similar to those of poison ivy. See Sumac. Poison ivy, poison oak, and poison sumac contain a lacquerlike resin in their sap. The resin is composed of active substances that provoke a sensitizing reaction in most, if not all, persons the first time effective contact occurs. Contact may be made by brushing past the leaves or the bare stems. Contact with exposed pets, clothing, or garden tools many induce a reaction. Smoke from burning ivy plants may carry the resin and affect all uncovered parts of the body. After a person has become sensitized, subsequent contact with the resin produces the typical allergic reaction of ivy poisoning. The effects do not become apparent for some hours. First, the skin reddens and begins to itch. Small watery blisters soon appear, often in lines indicating the point of contact with the plant, and the itching becomes intense. Finally, in severe cases, large watery swellings appear and coalesce. The condition is self-limiting, and recovery takes place in one to four weeks, even without treatment. A physician should be consulted in severe cases or if sensitive parts of the body, such as the eyelids, become involved. Scratching slows healing, invites infection, and may spread the resin from one location to another; the watery fluid in the blisters does not spread the reaction. Boric acid solution or calamine lotion are commonly used to relieve itching. Some or all of the resin may be removed by prompt and vigorous scrubbing with strong soap. Persons whose occupation exposes them to poison ivy, poison oak, or poison sumac should consider desensitization. See also Allergy. Scientific classification: Poison ivy, poison oak, and poison sumac belong to the genus Toxicodendron of the family Anacardiaceae. Poison ivy and poison oak are variants of Toxicodendron radicans. Poison sumac is classified as Toxicodendron vernix. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.

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