Gourt Home::Gourt :: Poison ivy
Poison ivy (Toxicodendron radicans or Rhus toxicodendron), in the family Anacardiaceae, rhus is also called Sumac. The name is often spelled "Poison-ivy" to indicate that it is not a true Ivy or Hedera. It is a woody vine that is well-known for its ability to produce urushiol, a skin irritant that causes an itching rash for most people, technically known as urushiol-induced contact dermatitis. In extreme cases, corticosteroids can be used to treat rashes.
Habitat and range
Poison ivy grows vigorously throughout much of North America. 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 various supports. 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.
Poison ivy (and oak) rarely grow at altitudes above 1500 m (5,000 feet).
Effects on the body
The reaction caused by poison ivy, urushiol-induced contact dermatitis, is an allergic reaction. For this reason some people claim to be "immune" to its "poisonous" effects. However, sensitivity can develop over time. For those who are affected by it, it causes a very irritating rash. If poison ivy is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. If poison ivy is eaten, the digestive tract and airways will be affected, in some cases causing death.
Characteristic appearance
The leaves are compound with three almond-shaped leaflets, giving rise to the mnemonic, "Leaves of 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), turning 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 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 resemblance 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.
Dead poison ivy still has plenty of urushiol, and will cause the same effect. The thick vines of grape, with no rootlets visible, differ from the vines of poison ivy, which have so many rootlets that the stem going up a tree looks furry.
See also
- Toxicodendron - an overview of plants with characteristics like poison ivy.
- Urushiol, poison ivy's toxin
- Burow's solution, for treating poison ivy injuries
- Poison Oak , Poison Sumac
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
- Poison ivy myths
- Links to pictures (Hardin MD/Univ of Iowa)
- photos and stories
- Toxicodendron radicans images at bioimages.vanderbilt.edu
Sapindales | Poisonous plants | Dermatology
Toxicodendron radicans | Toxicodendron radicans | Giftefeu | sumac grimpant | Gifsumak
"Poison ivy"