This weed was introduced from Europe, but why is not clear. The name comes from the French guiller, to ferment, because the leaves were once used to help ferment beer. The leaves are mint-flavored. Sometimes it is mistaken for , which is in the same family. Unlike plants with thorns that are obnoxious but serve the purpose of self-defense, Poison Ivy seems like pure evil. The worst time of year for Poison Ivy attacks is the spring before the leaves appear, where the plant is hard to distinguish from other vegetation. The stems are just as deadly as the leaves. Roundup (surgically applied near bodies of water), is a safe and effective herbicide that usually disposes of Poison Ivy with a single application that wets almost every leaf.
The oil, urushiol, is also found in Poison Sumac and Poison Oak, and 50%-70% of the U.S. population is allergic to it. Many people develop an allergy later in life, after being sensitized to it. Allergy to Poison Ivy can also mean you are allergic to cashew oil and mango fruit peels.
The vine will grow to the top of a 50' pine tree, with a woody stem several inches in diameter. This evil menace is valuable winter forage for wildlife, and its fruits are eaten by many birds.
Do not confuse Poison Ivy with the harmless having 5 leaflets, but sometimes 3 when first emerging. The two vines often grow together, intermingled and can be easy to confuse. While there are a few other vines with 3 leaflets, most (including the ) have fully serrated leaves rather than just a few jaggies, and only Poison Ivy has the center leaflet on a short stem (rachis). Like other Arums ( and ) it has a hood (spathe) covering a spadix containing the actual flowers. The root has calcium oxalate crystals that burns the mouth when raw, but can be eliminated by cooking, and Indians gathered them as a vegetable. There are several similar Joe Pye Weeds in the northeast, very tall (up to 10') and robust with pink fuzzy flowers. The specimen pictured here was completely bent over by the pond. This is the more common of the two Joe Pye Weeds in this catalog. According to folkore an Indian named Joe Pye used this plant to cure fevers, and early colonists used it to treat typhus. This is an annual or short-lived perennial that is typically planted, but for some reason one year we saw several specimens growing wild in this area. This is an introduced, invasive plant that can be a significant pset. It is aggressive, producing over 1000 seeds at a time, sucks up water faster than its neighbors, has few natural enemies, and may even release a toxin harmful to the roots of nearby plants. The flower has 5 lobes, which branch into many segments so it appears thistle-like. Knotweeds, , and comprise a genus of weedy plants with spikes of very small flowers.