词条 | Toxicodendron radicans | |||||||
释义 |
|name = Poison ivy |image = 2014-10-29 13 43 39 Poison Ivy foliage during autumn leaf coloration in Ewing, New Jersey.JPG |image_caption = Poison ivy during autumn |image2 =Toxicodendron radicans, leaves.jpg |image2_caption = Poison ivy in spring, Ottawa, Ontario |image2_alt = Photograph of green poison ivy leaves |status = G5 |status_system = TNC |genus = Toxicodendron |species = radicans |authority = (L.) Kuntze |range_map = Eastern Poison Ivy Range.png |range_map_caption = Toxicodendron radicans range map in North America |synonyms =
}} Toxicodendron radicans, commonly known as eastern poison ivy[1] or poison ivy, is a poisonous Asian and Eastern North American flowering plant that is well-known for causing urushiol-induced contact dermatitis, an itchy, irritating, and sometimes painful rash, in most people who touch it. The rash is caused by urushiol, a clear liquid compound in the plant's sap.[2] The species is variable in its appearance and habit, and despite its common name, it is not a true ivy (Hedera), but rather a member of the cashew and pistachio family (Anacardiaceae). T. radicans is commonly eaten by many animals, and the seeds are consumed by birds,[3] but poison ivy is most often thought of as an unwelcome weed. DescriptionNumerous subspecies and/or varieties of T. radicans are known,[4] which can be found growing in any of the following forms; all of which have woody stems:
The deciduous leaves of T. radicans are trifoliate with three almond-shaped leaflets.[8] 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 {{convert|3|-|12|cm|in|abbr=on}} long, rarely up to {{convert|30|cm|in|abbr=on}}. 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.[9] 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 a defensive measure; rather, it helps the plant to retain water. It is frequently eaten by animals such as deer and bears.[10]
Distribution and habitatT. radicans grows throughout much of North America, including the Canadian Maritime provinces, Quebec, Ontario, Manitoba, and all U.S. states east of the Rocky Mountains,[11] as well as in the mountainous areas of Mexico up to around {{convert|1500|m|ft|abbr=on}}. Caquistle or caxuistle is the Nahuatl term for the species. It is normally found in wooded areas, especially along edge areas where the tree line breaks and allows sunshine to filter through. It also grows in exposed rocky areas, open fields, and disturbed areas. It may grow as a forest understory plant, although it is only somewhat shade-tolerant.[8] The plant is extremely common in suburban and exurban areas of New England, the Mid-Atlantic, and the Southeastern United States. The similar species T. diversilobum (western poison oak) and T. rydbergii (western poison ivy) are found in western North America, and T. orientale in Taiwan, Japan, Korea and Sakhalin. T. radicans rarely grows at altitudes above {{convert|1500|m|ft|abbr=on}}, although the altitude limit varies in different locations.[8] The plants can grow as a shrub up to about {{convert|1.2|m|ft|abbr=on}} tall, as a groundcover {{convert|10|-|25|cm|in|abbr=on}} high, or as a climbing vine on various supports. Older vines on substantial supports send out lateral branches that may be mistaken for tree limbs at first glance. It grows in a wide variety of soil types, and soil pH from 6.0 (acidic) to 7.9 (moderately alkaline). It is not particularly sensitive to soil moisture, although it does not grow in desert or arid conditions. It can grow in areas subject to seasonal flooding or brackish water.[8] It is more common now than when Europeans first arrived in North America. The development of real estate adjacent to wild, undeveloped land has engendered "edge effects", enabling poison ivy to form vast, lush colonies in these areas. It is listed as a noxious weed in the US states of Minnesota and Michigan and in the Canadian province of Ontario. Outside North America, T. radicans is also found in parts of China.[7] Poison ivy is particularly sensitive to carbon dioxide levels, greatly benefiting from higher concentrations in the atmosphere. Higher carbon dioxide levels increase the rate of plant growth, and causes them to produce more unsaturated urushiol, which causes stronger reactions in humans.[12] Poison ivy's growth and potency has already doubled since the 1960s, and it could double again once carbon dioxide levels reach 560 ppm.[10] {{clear left}}Health effects{{Main|Urushiol-induced contact dermatitis}}Urushiol-induced contact dermatitis is the allergic reaction caused by poison ivy. In extreme cases, a reaction can progress to anaphylaxis. Around 15 to 25 percent of people have no allergic reaction to urushiol, but most people have a greater reaction with repeated or more concentrated exposure.[13][14] Typically, the rash from the urushiol oil lasts about five to twelve days, but in extreme cases it can last a month or more. [15] Over 350,000 people are affected by urushiol annually in the United States.[16] The pentadecylcatechols of the oleoresin within the sap of poison ivy and related plants causes the allergic reaction; the plants produce a mixture of pentadecylcatechols, which collectively is called urushiol. After injury, the sap leaks to the surface of the plant where the urushiol becomes a blackish lacquer after contact with oxygen.[2][17] Urushiol binds to the skin on contact, where it causes severe itching that develops into reddish inflammation or uncoloured bumps, and then blistering. These lesions may be treated with Calamine lotion, Burow's solution compresses, dedicated commercial poison ivy itch creams, or baths to relieve discomfort,[18] though recent studies have shown some traditional medicines to be ineffective.[19][20] Over-the-counter products to ease itching—or simply oatmeal baths and baking soda—are now recommended by dermatologists for the treatment of poison ivy.[21] A plant-based remedy cited to counter urushiol-induced contact dermatitis is jewelweed, and a jewelweed mash made from the living plant was effective in reducing urushiol dermatitis, supporting ethnobotanical use, while jewelweed extracts had no positive effect in clinical studies.[22][23][24][25] Others argue that prevention of lesions is easy if one practices effective washing, using plain soap, scrubbing with a washcloth, and rinsing three times within 2-8 hours of exposure.[26] The oozing fluids released by scratching blisters do not spread the poison. The fluid in the blisters is produced by the body and it is not urushiol itself.[34] The appearance of a spreading rash indicates that some areas received more of the poison and reacted sooner than other areas or that contamination is still occurring from contact with objects to which the original poison was spread. Those affected can unknowingly spread the urushiol inside the house, on phones, door knobs, couches, counters, desks, and so on, thus in fact repeatedly coming into contact with poison ivy and extending the length of time of the rash. If this has happened, wipe down the surfaces with bleach or a commercial urushiol removal agent. The blisters and oozing result from blood vessels that develop gaps and leak fluid through the skin; if the skin is cooled, the vessels constrict and leak less.[27] If plant material with urushiol is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty.[34] If poison ivy is eaten, the mucus lining of the mouth and digestive tract can be damaged.[28] An urushiol rash usually develops within a week of exposure and can last 1-4 weeks, depending on severity and treatment. In rare cases, urushiol reactions may require hospitalization.[29] Urushiol oil can remain active for several years, so handling dead leaves or vines can cause a reaction. In addition, oil transferred from the plant to other objects (such as pet fur) can cause the rash if it comes into contact with the skin.[30][29] Clothing, tools, and other objects that have been exposed to oil should be washed to prevent further transmission. People who are sensitive to urushiol can also experience a similar rash from mangoes. Mangoes are in the same family (Anacardiaceae) as poison ivy; the sap of the mango tree and skin of mangoes has a chemical compound similar to urushiol.[31] A related allergenic compound is present in the raw shells of cashews.[32] Similar reactions have been reported occasionally from contact with the related Fragrant Sumac (Rhus aromatica) and Japanese lacquer tree. These other plants are also in the Anacardiaceae family. Treatment{{Main|Urushiol-induced contact dermatitis#Treatments}}Immediate washing with soap and cold water or rubbing alcohol may help prevent a reaction. Hot water should not be used, as it causes one's pores to open up and admit the oils from the plant.[33] During a reaction, Calamine lotion or diphenhydramine may help mitigate symptoms. Corticosteroids, either applied to the skin or taken by mouth, may be appropriate in extreme cases. An astringent containing aluminum acetate (such as Burow's solution) may also provide relief and soothe the uncomfortable symptoms of the rash.[34] By using a detergent, the urushiol can be emulsified to break it down so that it can be washed away more easily. Adding sand or a gritty substance to the detergent will exfoliate the skin, taking the emulsified oil with it. Mixing the abrasive with a dishwashing liquid, and rubbing it briskly over the affected areas for several minutes, will mix the urushiol into the detergent, allowing it to be flushed away. IdentificationThese four characteristics are sufficient to identify poison ivy in most situations: (a) clusters of three leaflets, (b) alternate leaf arrangement, (c) lack of thorns, and (d) each group of three leaflets grows on its own stem, which connects to the main vine. The appearance of poison ivy can vary greatly between environments, and even within a large area. Identification by experienced people is often made difficult by leaf damage, the plant's leafless condition during winter, and unusual growth forms due to environmental or genetic factors. Various mnemonic rhymes describe the characteristic appearance of poison ivy:[35]
Similar-looking plants
Similar allergenic plants
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B. |title = Cashew Nut Dermatitis |journal = Southern Medical Journal | volume = 87 | issue = 4 |pages = 543–546 |date = April 1994|doi = 10.1097/00007611-199404000-00026| pmid = 8153790 }} 33. ^{{cite web|url=http://www.teclabsinc.com/blog/2012/8/2/common-misconceptions-about-treating-poison-ivy-or-oak-rash|title=Misconceptions About Treating Poison Ivy and Oak Rash|work=teclabsinc.com|deadurl=yes|archiveurl=https://web.archive.org/web/20140826160923/http://www.teclabsinc.com/blog/2012/8/2/common-misconceptions-about-treating-poison-ivy-or-oak-rash|archivedate=2014-08-26|df=}} 34. ^{{cite journal|last1=Gladman|first1=Aaron C.|title=Toxicodendron Dermatitis: Poison Ivy, Oak, and Sumac|journal=Wilderness & Environmental Medicine|date=June 2006|volume=17|issue=2|pages=120–128|doi=10.1580/PR31-05.1|pmid=16805148}} 35. ^{{cite web |url=http://pediatrics.about.com/cs/conditions/a/poison_ivy_3.htm |title= Poison Ivy Treatment Guide, Getting Rid of the Plants: Identifying Poison Ivy |accessdate= |website= }} 36. ^{{cite book|author=Crosby, Donald G. |title=The Poisoned Weed: Plants Toxic to Skin|url=https://books.google.com/books?id=W4D1H1PEL-AC&pg=PA32|year=2004|publisher=Oxford University Press|isbn=978-0-19-515548-8|pages=32–}} 37. ^1 {{cite book|author=Jennings, Neil L. |title=In Plain Sight: Exploring the Natural Wonders of Southern Alberta|url=https://books.google.com/books?id=BuUCxztT6ycC&pg=PA105|year=2010|publisher=Rocky Mountain Books Ltd|isbn=978-1-897522-78-3|pages=105–}} 38. ^{{cite web|url=http://www.telemedicine.org/botanica/bot6.htm|title=Botanical Dermatology – ALLERGIC CONTACT DERMATITIS – ANACARDIACEAE AND RELATED FAMILIES|website=The Internet Dermatology Society, Inc|accessdate=22 Sep 2014}} External links{{Commons|Rhus radicans}}
7 : Allergology|Dioecious plants|Flora of North America|Medicinal plants|Poisonous plants|Toxicodendron|Vines |
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