“Leaflets three; let it be” is the best known and most useful cautionary rhyme. It applies to poison oak, as well as to poison ivy, but other, non-harmful plants have similar leaves.
“Hairy vine, no friend of mine. ”
“Berries white, run in fright” and “Berries white, danger in sight. ”
Toxicodendron radicans, commonly known as eastern poison ivy or poison ivy, is a poisonous Asian and North American 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 plant’s sap. 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.
There are numerous subspecies and/or varieties of T. radicans, which can be found growing in any of the following forms; all of which have woody stems:
as a climbing vine that grows on trees or some other support
as a shrub up to 1.2 metres (3 ft 11 in) tall
as a trailing vine that is 10–25 centimetres (3.9–9.8 in) tall
Urushiol-induced contact dermatitis is the allergic reaction caused by poison ivy. In extreme cases, a reaction can progress to anaphylaxis. Around 15% to 30% of people have no allergic reaction to urushiol, but most people will have a greater reaction with repeated or more concentrated exposure.