Toxicodendron radicans, commonly known as eastern poison ivy[1] or poison ivy, is a poisonous Asian and North American flowering plant that is well known for causing an itching, irritating, allergic and sometimes painful rash in most people who touch it, 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 almond family. Toxicodendron 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.
Description
There are numerous subspecies and/or varieties of T. radicans,[4] 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
- Subspecies and varieties[5]
- Toxicodendron radicans subsp. eximum (Greene) Gillis
- Toxicodendron radicans subsp. hispidum (Engl.) Gillis
- Toxicodendron radicans subsp. negundo (Greene) Gillis[6]
- 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[7]
- Toxicodendron radicans subsp. verrucosum (Scheele) Gillis
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 3–12 cm
(1.2–4.7 in) long, rarely up to 30 cm (12 in). 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]
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
8 cm (3.1 in) above the leaves. The berry-like fruit, a drupe, mature by August to November with a grayish-white colour.[8] 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.
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