Urushiol /ÊËruËÊi.Él/ is an oily mixture of organic compounds with allergenic and sensitizing properties found in plants of the family Anacardiaceae, especially Toxicodendron spp. (e.g., poison oak, Chinese lacquer tree, poison ivy, poison sumac), Comocladia spp. (maidenplums), Metopium spp. (poisonwood), and also in parts of the mango tree and the fruit of the cashew tree.
In most individuals, urushiol causes an allergic skin rash on contact, known as urushiol-induced contact dermatitis.
Toxicodendron is a genus of flowering plants in the sumac family, Anacardiaceae. It contains trees, shrubs and woody vines, including poison ivy, poison oak, and the lacquer tree. The best-known members of the genus in North America are eastern poison ivy (T. radicans) and western poison oak (T. diversilobum), both ubiquitous throughout much of their respective region.
All members of the genus produce the skin-irritating oil urushiol, which can cause a severe allergic reaction known as urushiol-induced contact dermatitis. The resins of certain species native to Japan, China and other Asian countries, such as lacquer tree (T. vernicifluum) and wax tree (T. succedaneum), are used to make lacquer, and, as a byproduct of lacquer manufacture, their berries are used to make japan wax.
Poison ivy is a type of allergenic plant in the genus Toxicodendron native to Asia and North America. Formerly considered a single species, Toxicodendron radicans, poison ivies are now generally treated as a complex of three separate species: T. radicans, T. rydbergii, and T. orientale. They are variable in appearance and habit, and despite its common name, it is not a true ivy (i.e., Hedera), but rather a member of the cashew and pistachio family (Anacardiaceae).
Though T. radicans is commonly eaten by many animals and the seeds are consumed by birds, poison ivy is most often thought of as an unwelcome weed. It is well known for causing urushiol-induced contact dermatitis, an itchy, irritating, and sometimes painful rash, in most people who touch them. The rash is caused by urushiol, a clear liquid compound in the plant's sap.
Aerial roots are roots growing above the ground. They are often adventitious, i.e. formed from nonroot tissue. They are found in diverse plant species, including epiphytes such as orchids (Orchidaceae), tropical coastal swamp trees such as mangroves, banyan figs (Ficus subg. Urostigma), the warm-temperate rainforest rata (Metrosideros robusta), and pÅhutukawa trees of New Zealand (Metrosideros excelsa). Vines such as common ivy (Hedera helix) and poison ivy (Toxicodendron radicans) also have aerial roots.