Western poison-Ivy is a species of drier slopes,
most commonly in Interior British Columbia.
Toxicodendron
radicans, commonly known as poison-ivy (older synonyms are Rhus toxicodendron
and Rhus radicans), is a poisonous North American plant that is well known
for its production of urushiol, a clear liquid compound found within the sap of
the plant that causes an itching, irritation and sometimes painful rash in most
people who touch it. The plant is not a true ivy.
The
deciduous leaves of poison ivy are trifoliate with three almond-shaped
leaflets. Leaf colour 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 one to five inches long, rarely up to twelve inches. 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 3 inches above the leaves.
The berry-like fruit, a drupe, mature by August to November with a
grayish-white colour. Fruits are a favourite winter food of some birds and
other animals. Seeds are spread mainly by animals and remain viable after
passing through the digestive tract.
Poison-ivy
can be found growing in any of the following forms:
As a
trailing vine that is four to ten inches tall
As a
shrub up to four feet tall
As a
climbing vine that grows on trees or some other support
Distribution
and Habitat
Poison
ivy grows throughout much of North America, including the Canadian Maritime
provinces, Quebec, Ontario, Manitoba, and all U.S. states East
of the Rocky Mountains,
as well as in the mountainous areas of Mexico up to around 4,900 ft. It is
normally found in wooded areas, especially along edge areas where the tree line
breaks and allows sunshine to filter through. It also grows in exposed rocky
areas, open fields and disturbed areas.
Toxicodendron
radicans may grow as a forest understory plant, although it is only somewhat
shade tolerant. The plant is extremely common in suburban and exurban areas of
New England, the Mid-Atlantic, and south-eastern United States.
A
Similar species, poison oak, and Toxicodendron rydbergii
are found
in western North America. Poison ivy rarely grows at altitudes above (4,900 ft.), although the altitude limit
varies in different locations The plants can grow as a shrub up to about four feet tall, as a groundcover four to ten inches high, or as a climbing vine on various
supports. Older vines on substantial supports send out lateral branches that
may be mistaken for tree limbs at first glance.
It
grows in a wide variety of soil types, and soil pH from 6.0 (acidic) to 7.9
(moderately alkaline). It is not particularly sensitive to soil moisture,
although it does not grow in desert or arid conditions. It can grow in areas
subject to seasonal flooding or brackish water.
It is more
common now than when Europeans first arrived in North America. A study found that poison-ivy
is particularly sensitive to CO2 levels, greatly benefiting from higher CO2 in
the atmosphere. Poison ivy's growth and potency has already doubled since the
1960s, and it could double again once CO2 levels reach 560 ppm. The development
of real estate adjacent to wild, undeveloped land has engendered "edge
effects," enabling poison ivy to form vast, lush colonies in these areas.
It is listed as a noxious weed in the Canadian province of Ontario.
Outside
North America, poison-ivy is also found in the temperate parts of Asia, in
Japan, Taiwan, the Russian islands of Sakhalin and the Kuriles, and in parts of
China.
The following four characteristics are sufficient
to identify poison ivy in most situations:
(a) clusters of three leaflets,
(b)
alternate leaf arrangement,
(c) lack of thorns, and
(d) 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. 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.
Various
mnemonic rhymes describe the characteristic appearance of poison ivy:
"Leaflets
three; let it be" is the best known and most useful cautionary rhyme. It
applies to poison oak, as well as to poison-ivy.
"Hairy
vine, no friend of mine."
"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 Rhus aromatica (fragrant sumac).
"Raggy
rope, don't be a dope!" Poison ivy vines on trees have a furry
"raggy" appearance. This rhyme warns 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.
"One,
two, three? Don't touch me."
"Berries
white, run in fright" and "Berries white, danger in sight."
"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.)
"If
it's got hair, it won't be fair." This refers to the hair that can be on
the stem and leaves of poison ivy.
Blisters from Contact with Poison ivy
The
oozing fluids released by scratching blisters do not spread the poison. The
fluid in the blisters is produced by the body and it is not urushiol
itself.The appearance of a spreading rash indicates that some areas
received more of the poison and reacted sooner than other areas or that
contamination is still occurring from contact with objects to which the
original poison was spread.
The blisters and oozing result from blood vessels that
develop gaps and leak fluid through the skin; if the skin is cooled, the
vessels constrict and leak less. 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 mucus lining of the mouth and digestive tract can be
damaged. A poison ivy rash usually develops within a week of exposure and
can last anywhere from one to four weeks, depending on severity and treatment.
In rare cases, poison ivy reactions may require hospitalization.
Urushiol
oil can remain active for several years, so handling dead leaves or vines can
cause a reaction. In addition, oil transferred from the plant to other objects (such
as pet fur) can cause the rash if it comes into contact with the skin. Clothing, tools, and other objects that have been exposed to the oil should be
washed to prevent further transmission.
People
who are sensitive to poison ivy can also experience a similar rash from
mangoes. Mangoes are in the same family (Anacardiaceae) as poison ivy; the sap
of the mango tree and skin of mangoes has a chemical compound similar to
urushiol. A related allergenic compound is present in the raw shells of cashews. Similar reactions have been reported occasionally from contact with the related
Fragrant Sumac (Rhus aromatica) and Japanese lacquer tree. These other plants
are also in the Anacardiaceae family.
Treatment of Poison ivy Rash
Immediate
washing with soap and water or rubbing alcohol may help prevent a reaction.
During a reaction, Calamine lotion or diphenhydramine may help mitigate
symptoms. Corticosteroids, either applied to the skin or taken by mouth, may be
appropriate in extreme cases.
Urushiol
binds to the skin on contact, where it causes severe itching that develops into
reddish coloured inflammation or non-coloured bumps, and then blistering. These
lesions may be treated with Calamine lotion, Burow's solution compresses or
baths to relieve discomfort though recent studies have shown some traditional
medicines to be ineffective] Over-the-counter products to ease itching—or
simply oatmeal baths and baking soda—are now recommended by dermatologists for
the treatment of poison ivy.
A plant based remedy cited to counter urushiol
induced contact dermatitis is jewelweed. "The results of a clinical study,
in which a 1:4 jewelweed preparation was compared for its effectiveness with
other standard poison ivy dermatitis treatments was published in 1958 Of 115
patients treated with jewelweed, 108 responded ‘most dramatically to the
topical application of this medication and were entirely relieved of their
symptoms within 2 or 3 days after the institution of treatment.' It was
concluded that jewelweed is an excellent substitute for ACTH and the
corticosteroids in the treatment of poison ivy dermatitis.
Other sources have since concluded that jewelweed is ineffective or of
questionable effectiveness.
Box-elder, a harmless ornamental tree, found on many lawns and boulivards (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.
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 colour, 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 centre leaflet of poison ivy is on a long
stalk, while the centre 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 colour and is covered with tiny hairs while
poison ivy fruit is smooth and ripens to a whitish colour.
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. ©Al (Alex-Alexander) D Girvan. All rights reserved.