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''Toxicodendron radicans'', commonly known as poison ivy (older synonyms are ''Rhus toxicodendron'' and ''Rhus radicans''),〔USDA Fire Effects Information System: (''SPECIES: Toxicodendron radicans, T. rydbergii'' )〕 is a poisonous North American and Asian flowering plant that is well known for causing an itching, irritating, and sometimes painful rash in most people who touch it, caused by urushiol, a clear liquid compound in the sap of the plant. The species is variable in its appearance and habit, and despite its common name it is not a true ivy (''Hedera''). ''Toxicodendron radicans'' is commonly eaten by many animals, and the seeds are consumed by birds, but poison ivy is most often thought of as an unwelcome weed. == Description == There are numerous subspecies and/or varieties of ''T. radicans'', which can be found growing in any of the following forms, all have woody stems: * as a trailing vine that is tall * as a shrub up to tall * as a climbing vine that grows on trees or some other support ;Subspecies and varieties〔(The Plant List, ''Toxicodendron radicans'' (L.) Kuntze )〕 *''Toxicodendron radicans'' subsp. ''eximum'' (Greene) Gillis *''Toxicodendron radicans'' subsp. ''hispidum'' (Engl.) Gillis *''Toxicodendron radicans'' subsp. ''negundo'' (Greene) Gillis〔(【引用サイトリンク】title=Tropicos – Name – Toxicodendron radicans subsp. negundo (Greene) Gillis )〕 *''Toxicodendron radicans'' var. ''negundo'' (Greene) Reveal *''Toxicodendron radicans'' var. ''pubens'' (Engelm. ex S. Watson) Reveal *''Toxicodendron radicans'' subsp. ''radicans'' *''Toxicodendron radicans'' var. ''radicans'' *''Toxicodendron radicans'' subsp. ''rydbergii'' (Small ex Rydb.) Á. Löve & D. Löve *''Toxicodendron radicans'' var. ''rydbergii'' (Small ex Rydb.) Erskine〔(【引用サイトリンク】title=Toxicodendron radicans var. rydbergii (Small ex Rydberg) Erskine )〕 *''Toxicodendron radicans'' subsp. ''verrucosum'' (Scheele) Gillis The deciduous leaves of ''T. radicans'' are trifoliate with three almond-shaped leaflets.〔 Leaf color ranges from light green (usually the younger leaves) to dark green (mature leaves), turning bright red in fall; though other sources say leaves are reddish when expanding, turn green through maturity, then back to red, orange, or yellow in the fall. The leaflets of mature leaves are somewhat shiny. The leaflets are long, rarely up to . Each leaflet has a few or no teeth along its edge, and the leaf surface is smooth. Leaflet clusters are alternate on the vine, and the plant has no thorns. Vines growing on the trunk of a tree become firmly attached through numerous aerial rootlets.〔Petrides, George A. ''A Field Guide to Trees and Shrubs'' (Peterson Field Guides), Boston: Houghton Mifflin Co., 1986, p. 130.〕 The vines develop adventitious roots, or the plant can spread from rhizomes or root crowns. The milky sap of poison ivy darkens after exposure to the air. The urushiol compound in poison ivy is not meant as a defensive measure; rather, it helps the plant to retain water. It is frequently eaten by animals such as deer and bears. ''Toxicodendron radicans'' spreads either vegetatively or sexually. It is dioecious; flowering occurs from May to July. The yellowish- or greenish-white flowers are typically inconspicuous and are located in clusters up to above the leaves. The berry-like fruit, a drupe, mature by August to November with a grayish-white colour.〔 Fruits are a favorite winter food of some birds and other animals. Seeds are spread mainly by animals and remain viable after passing through the digestive tract. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Toxicodendron radicans」の詳細全文を読む スポンサード リンク
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