Poison-ivy
From Freepedia
- For other uses, see Poison ivy (disambiguation).
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| Image:Poison ivy lg.jpg Poison-ivy | ||||||||||||||
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| Toxicodendron radicans (L.) Kuntze |
Poison-ivy (Toxicodendron radicans or Rhus toxicodendron), in the family Anacardiaceae, is a woody vine that is well-known for its ability to produce urushiol, a skin irritant which for most people will cause an agonizing, itching rash.
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Habitat and range
Poison-ivy grows vigorously throughout much of North America, but particularly in the American Midwest. It can grow as a shrub up to about 1.2 m (4 ft) tall, as a groundcover 10-25 cm (4-10 in) high, or as a climbing vine on any and every support. Older vines on substantial supports send out lateral branches that may at first be mistaken for tree limbs.
Poison-ivy is apparently far more common now than when the Europeans first entered North America because it has profited immensely from the "edge effect", enabling it to form lush colonies in such places.
How to recognize poison-ivy
The leaves are compound with three almond-shaped leaflets, giving rise to the mnemonic, "Leaflets three, let it be". The berries (actually drupes) are a grayish-white color and are a favorite winter food of some birds.
The color ranges from light green (usually the younger leaves) to dark green (mature leaves), and bright red in fall. The leaflets are 3-12 cm long, rarely up to 30 cm. Each leaflet has a few or no teeth along its edge, and the leaf surface is smooth. To compare, blackberry and raspberry leaves also come in threes, but they have many teeth along the leaf edge, and the top surface of their leaves are very wrinkled where the veins are. The stem and vine are smooth, brown and woody, while blackberry stems are green with thorns.
Virginia creeper (Parthenocissus quinquefolia) vine can look like poison-ivy. The younger leaves can come in groups of three but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. Virginia creeper and poison-ivy very often grow together, even on the same tree.
Western Poison-oak leaves also come in threes on the end of a stem, but each leaf is shaped somewhat like an oak leaf. Western Poison-oak only grows in the western United States, although many people will refer to poison-ivy as poison-oak. This is because poison-ivy will grow in either the ivy-like form or the brushy oak-like form depending on the moisture and brightness of its environment. The ivy form likes shady areas with only a little sun, and tends to climb the trunks of trees, and can spread rapidly along the ground.
Blackberry vines bear a passing resemblence to poison ivy, with whose climate they overlap. The chief difference with blackberry vines is that they have spines on them, whereas poison ivy is smooth. Also, the three-leaf pattern of the leaves changes as the plant grows: the two bottom leaves both split into two leaves, for a total of five in a cluster.
Beware of dead poison-ivy: it still has plenty of urushiol, and will give the same effect. Compare the thick vines of grape, with no rootlets visible, to the vines of poison-ivy, with so many rootlets that the stem going up a tree looks furry.
Avoidance, treatment, and safety
For specific information on prevention and treatment of Toxicodendron rashes, see Urushiol-induced contact dermatitis.
Note on name hyphenation
The hyphenated form "Poison-ivy" is used, rather than "Poison Ivy" to clearly indicate that it is not a variety of ivy, just as "Poison-oak" is not a variety of oak.
External links
- How Stuff Works: Poison-ivy
- The Poison-ivy tutorial
- Contact-poisonous Plants of the World
- Treating Poison-ivy, Poison-oak, or Poison Sumac
- Plant and Rash photos
- Poison-ivy myths
