Poison Ivy
Toxicodendron radicans | Anacardiaceae
Submission: Amelia Wallis and Hugh Piper
Identification:
Leaves – alternate, trifoliate, 7-10” long, ovate, irregularly toothed, green above but paler on the underside.
Twigs – slender, gray to red brown, with aerial roots that become dense and hairy with age. Branches grow 90 degrees from the plant, and buds are stalked, naked, fuzzy brown, and a ¼” long (see image below).
Fruit – Greenish white, round (¼” in diameter), and borne in clusters. They ripen in the late summer but are persistent through the winter.
Flowers – grow in small clusters that are yellowish green and appear in late spring to early summer.
Bark – dark gray and densely covered in aerial roots.
Natural History:
“Leaflets three, let it be.” If you grew up in North America, you have probably heard this saying before. It refers to poison ivy and poison oak; plants within the Anacardiaceae family that have three leaflets and possess toxic properties. So take caution when identifying these plants and do not come in direct contact, as the oils can cause minor to severe skin rashes and swelling.
Poison ivy (Toxicodendron radicans) is native to North America. Aside from having trivariate leaves, it is often identified by its serrated leaf margins and a lush green leaf color that can be either glossy or dull. It commonly grows in full sun to partially shaded environments, and is adaptable to different soil types. It is frequently found in disturbed sites–particularly forest edges and river banks–but as a vine it also uses aerial roots to attach itself to structures including tree trunks and buildings. In the fall, the leaves turn a brilliant red.
Historically, our first references to poison ivy come from 7th century China and 10th century Japan. Toxicodendron species don’t grow in Europe natively, so Europeans didn’t come into contact with poison ivy until their colonization of the Americas. Although Colonists first contact with poison ivy was negative, Indigenous Americans had developed many uses of the plant. There is evidence that the Meskwaki, Ojibwe, and Potawatomi made a poultice from the plant to be used to treat swelling. Ramah Navajos used a mix of poison ivy sap, deer blood, and charcoal to make poison for arrowheads. Indigenous Americans on the west coast used poison oak leaves in cooking and in addition to using the sap to treat warts, rattlesnake bites, and ringworm.
Sensitivity to poison ivy can vary from person to person and over a single person’s life. There are around 2 million cases of dermatitis per year caused by poison ivy and its relatives. It is the most common reason for workers compensation claims and the most common injury for US Forest Service workers. Only humans and closely related primates have allergic reactions to poison ivy, so deer frequently browse it, and bees collect nectar from the flowers.
References:
Poison-Ivy / Poison-Oak / Poison-Sumac: The Virulent Weeds. Weed Science Society of America; [accessed 2023 Nov 30]. https://wssa.net/wp-content/themes/WSSA/WorldOfWeeds/poisonivy.htm
Poison Ivy. 2021. Virginia Tech Department of Forest Resources and Environmental
Conservation; [accessed 2021, Nov 26]
Rhus radicans, Poison ivy, Anacardiaceae. 2015. University of Connecticut. College of
Agriculture, Health, and Natural Resources; [Accessed 20213 Nov 26].
(Source: Mass Audubon)
First 2 pictures taken outside Merrill woods