Poison ivy

Poison ivy (Toxicodendron radicans or formerly Rhus toxicodendron or Rhus radicans) is a plant in the family Anacardiaceae. The name is often spelled "Poison-ivy" to indicate that it is not a true Ivy (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.

Identification
The deciduous leaves of poison ivy are trifoliate with three almond-shaped leaflets. 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. 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.

Poison ivy spreads either vegetatively or sexually. Poison ivy 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. 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.

Basic characteristics
The following four characteristics are sufficient to identify poison ivy in most situations:


 * 1) clusters of three leaflets
 * 2) alternate leaf arrangement
 * 3) lack of thorns
 * 4) each group of three leaflets grows on its own stem, which connects to the main vine

The appearance of poison ivy can vary greatly between environments, and even within a single area. Poison ivy can be found growing in any of the following forms:


 * as a trailing vine that is 10–25 centimeters (3.9–9.8 in) tall
 * as a shrub up to 1.2 meters (3 ft 11 in) tall
 * as a climbing vine that grows on trees or some other support

Identification by experienced people is often made difficult by leaf damage, the plant's leafless condition during winter, and unusual growth forms due to environmental or genetic factors.

Mnemonic rhymes
Various mnemonic rhymes describe the characteristic appearance of poison ivy:




 * Regarding the leaves:
 * "Leaves of three; let it be." or "Leaves of three; leave it be." also "One, two, three? Don't touch me."
 * Probably the most well known fact about poison ivy is that it has trifoliate compound leaves with three leaflets.
 * "Longer middle stem; stay away from them."
 * This refers to the middle leaflet having a visibly longer stem than the two side leaflets and is a key to differentiating it from the similar-looking fragrant sumac (Rhus aromatica).
 * "Red leaflets in the spring, it's a dangerous thing."
 * This refers to the red appearance that new leaflets sometimes have in the spring. (Note that later, in the summer, the leaflets are green, making them more difficult to distinguish from other plants, while in autumn they can be reddish-orange.)
 * "Side leaflets like mittens, will itch like the dickens."
 * This refers to the appearance of some, but not all, poison ivy leaves, where each of the two side leaflets has a small notch that makes the leaflet look like a mitten with a "thumb." (Note that this rhyme should not be misinterpreted to mean that only the side leaflets will cause itching, since actually all parts of the plant can cause itching.)
 * Regarding the vine:
 * "Hairy vine, no friend of mine.", "Raggy rope, don't be a dope!" and "If it's got hair, it won't be fair."
 * Poison ivy vines also contain urushiol and can cause the rash as well as the leaves. The vines on trees have a hairy, furry or "raggy" appearance. These rhymes warn tree climbers to be wary. Old, mature vines on tree trunks can be quite large and long, with the recognizable leaves obscured among the higher foliage of the tree.
 * Regarding the berries:
 * "Berries white, run in fright" and "Berries white, danger in sight."
 * The berries generally stay on the plant throughout the winter and aid in identification when the deciduous leaves have fallen away.

Similar-looking plants



 * Virgin's Bower (Clematis virginiana) (also known as Devil's Darning Needles, Devil's Hair, Love Vine, Traveller's Joy, Virginia Virgin's Bower, Wild Hops, and Woodbine; syn. Clematis virginiana L. var. missouriensis (Rydb.) Palmer & Steyermark [1]) is a vine of the Ranunculaceae family native to the United States. This plant is a vine that can climb up to 10–20 ft tall. It grows on the edges of the woods, moist slopes, and fence rows, and in thickets and streambanks. It produces white, fragrant flowers about an inch in diameter between July and September.




 * Box-elder (Acer negundo) saplings have leaves that can look very similar to those of poison ivy, although the symmetry of the plant itself is very different. While box-elders often have five or seven leaflets, three leaflets are also common, especially on smaller saplings. The two can be differentiated by observing the placement of the leaves where the leaf stalk meets the main branch (where the three leaflets are attached). Poison ivy has alternate leaves, which means the three-leaflet leaves alternate along the main branch. The maple (which the box-elder is a type of) has opposite leaves; another leaf stalk directly on the opposite side is characteristic of box-elder.


 * Virginia creeper (Parthenocissus quinquefolia) vines can look like poison ivy. The younger leaves can consist of three leaflets but have a few more serrations along the leaf edge, and the leaf surface is somewhat wrinkled. However, most Virginia creeper leaves have five leaflets. Virginia creeper and poison ivy very often grow together, even on the same tree. Be aware that even those who do not get an allergic reaction to poison ivy may be allergic to the oxalate crystals in Virginia creeper sap.




 * Western Poison-oak (Toxicodendron diversilobum) leaflets also come in threes on the end of a stem, but each leaflet is shaped somewhat like an oak leaf. Western Poison-oak grows only in the western United States and Canada, 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, tends to climb the trunks of trees, and can spread rapidly along the ground.




 * Poison Sumac (Toxicodendron vernix) has compound leaves with 7–15 leaflets. Poison sumac never has only three leaflets.




 * Kudzu (Pueraria lobata) is a non-toxic edible vine that scrambles extensively over lower vegetation or grows high into trees. Kudzu is an invasive species in the southern United States. Like poison ivy, it has three leaflets, but the leaflets are bigger than those of poison ivy and are pubescent underneath with hairy margins.


 * Blackberries and raspberries (Rubus spp.) can resemble poison ivy, with which they may share territory; however, blackberries and raspberries almost always have thorns on their stems, whereas poison ivy stems are smooth. Also, the three-leaflet pattern of some blackberry and raspberry leaves changes as the plant grows: Leaves produced later in the season have five leaflets rather than three. Blackberries and raspberries have many fine teeth along the leaf edge, the top surface of their leaves is very wrinkled where the veins are, and the bottom of the leaves is light minty-greenish white. Poison ivy is all green. The stem of poison ivy is brown and cylindrical, while blackberry and raspberry stems can be green, can be squared in cross-section, and can have prickles. Raspberries and blackberries are never truly vines; that is, they do not attach to trees to support their stems.




 * The thick vines of Riverbank Grape (Vitis riparia), 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. Riverbank grape vines are purplish in color, tend to hang away from their support trees, and have shreddy bark; poison ivy vines are brown, attached to their support trees, and do not have shreddy bark.




 * Fragrant Sumac (Rhus aromatica) has a very similar appearance to poison ivy. While both species have three leaflets, the center leaflet of poison ivy is on a long stalk, while the center leaflet of fragrant sumac does not have an obvious stalk. When crushed, fragrant sumac leaves have a fragrance similar to citrus while poison ivy has little or no distinct fragrance. Fragrant sumac produces flowers before the leaves in the spring, while poison ivy produces flowers after the leaves emerge. Flowers and fruits of fragrant sumac are at the end of the stem, but occur along the middle of the stem of poison ivy. Fragrant sumac fruit ripens to a deep reddish color and is covered with tiny hairs while poison ivy fruit is smooth and ripens to a whitish color.




 * Hoptree (Ptelea trifoliata) has leaves that are remarkably similar. It is, however, a much larger plant so confusion is unlikely for any but the smallest specimens. The flowers and seeds are also easily distinguished from those of poison ivy.

Origin, Distribution, Habitat, and Life Cycle


Origin
 * Poison ivy is native to the continent of North America

Distribution
 * Poison ivy grows vigorously throughout much of North America. It is believed to be 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.

Habitat
 * It is normally found in wooded areas, especially along edge areas. It also grows in exposed rocky areas and in open fields and disturbed areas.

Life Cycle
 * Poison ivy is a perennial plant.

Phenology
 * Flowers: May to July
 * Berries: August to November

Etymology

 * The specific name radicans means "with rooting stems" . While the generic name is composed of Toxico meaning "poisonous" and dendron meaning "tree" . Therefore the full binomial could be interpreted as "the poisonous tree with rooting stems".

Stories

 * See The Guardian

Myths
There are many myths that deal with treating toxicodendrons such as poison ivy. Most have been discredited, but some persist despite their falsehood:


 * The fluid from the resulting blisters spreads poison ivy to others.
 * Poison ivy is harmless when the leaves have fallen off.
 * Ice, water, soap, lotions, dry cold air, can help cure poison ivy rash faster. In reality, skin cells react to the urushiol even after the urushiol has been washed off, and the methods listed are for soothing the rash.

Attribution
Portions of this page were copied from Toxicodendron radicans and/or recovered from rewild.info