Toxicodendron radicans (L.) Kuntze
The words or terms in red
(actually dark orange) in the text are defined in a
Toxicodendron radicans is a woody low
shrub that is erect or trailing,
or is a climbing vine.
It 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.
The plant is native to North America.
It is listed as a noxious weed in the U.S. states of Minnesota and Michigan
and the Canadian province of Ontario where it readily forms colonies.
Toxicodendron radicans is a highly variable
there is considerable disagreement over whether Toxicodendron radicans
is one species with variations
and varieties or
subspecies, or many separate species.
Many botanists recognize 7 subspecies in
the Toxicodendron radicans species, namely:
Other botanists consider some of theses subspecies, like the radicans
subspecies as mere varieties in the
species. Other still, in Québec notably, consider a species like
Toxicodendron rydbergii as a
variety of Toxicodendron radicans i.e. with the name
Toxicodendron radicans var. rydbergii.
This seems to point to the fact that the Toxicodendron
genus is still not
well-known enough biologically and one will have to wait for a while
before botanists agree on the specificity of the
- Toxicodendron radicans (L.) Kuntze subsp. barkleyi
- Toxicodendron radicans (L.) Kuntze subsp. divaricatum
- Toxicodendron radicans (L.) Kuntze subsp. eximium
- Toxicodendron radicans (L.) Kuntze subsp. negundo
- Toxicodendron radicans (L.) Kuntze subsp. pubens
- Toxicodendron radicans (L.) Kuntze subsp. radicans
- Toxicodendron radicans (L.) Kuntze subsp. verrucosum
The species belongs to the
In classical Greek one of the meaning of
(toxicos) is poison with which the tip of an arrow is soaked.
In Latin this became toxicum with the same meaning and the more
general meaning of poison and laudanum (an opium extract once
used for various medical purposes and as a recreational drug), and this is
the root of the word toxic and of its derivatives.
In classical Greek
means tree, and all species of the
Toxicodendron genus are shrubs or small trees that are quite toxic.
In Latin, the verb radicare means to root, and radicans
is its present participle, the
epithet refers then to the fact that
Toxicodendron radicans roots easily.
The vernacular name of
Toxicodendron radicans is Poison Ivy.
The French vernacular names are
Herbe à la puce, Herbe à puce, Sumac grimpant, Toxicodendron grimpant.
Toxicodendron radicans has also been known as:
- Rhus radicans L.
- Rhus radicans L. var. littoralis (Mearns) Deam
- Rhus radicans L. var. malacotrichocarpa (A. H. Moore)
- Toxicodendron vulgare Mill.
- Toxicodendron negundo Greene
- Toxicodendron radicans (L.) Kuntze var. negundo
It is quite important to be able to identify readily
Toxicodendron radicans whether in its climbing or non climbing form;
its field marks are :
The leaflets may have smooth, scalloped or
irregularly toothed margins but
typically the lateral two leaflets have irregularly toothed outer leaf margins
and smooth, untoothed inner leaf margins. The middle leaflet is generally
larger than the two laterals.
- alternate leaves;
- the leaves are clusters of three leaflets with pointed tips;
- the stem is woody;
- the fruits are a grape of small round white balls that remains
on the plant in the winter;
In contrast, le Parthenocissus quinquefolia (the Virginia
Creeper), a non-poisonous vine often mistaken for poison ivy, has five leaflets radiating from one point of attachment.
The stems are initially light reddish green but become woody, brown;
they are smooth (though older stems of climbing plants
develop a very hairy appearance). They may trail along (or just under) the
ground, sending frequent branches both out and up. They may grow upright, in a
shrub form, which can reach 7 feet in height under good conditions.
Or they may grow as a vine, up to 5 inches in diameter, climbing trees and
fences by means of dense, dark, fibrous, aerial roots (giving the vines that
hairy look). They are toxic.
The caterpillars of Amorbia humerosana (Tortricid Moth sp.),
Marathyssa basalis (Light Marathyssa), and
Paectes oculatrix (Eyed Paectes)
feed on the foliage despite its toxicity.
- alternate and
palmately compound with long
- with 3 almond-shaped, ovate or
from 2 to 4 inches long and up to 3 inches wide,
with a densely pubescent
petiolule up to 5 mm long;
- each leaflet with a few irregular teeth, few in number and somewhat
blunt, or without teeth along its edge or with wavy edges;
- light green with a reddish cast when young, deep green, often shiny
when mature, turning bright red in the fall;
Bees are attracted by the nectar and
An individual plant may in fact have perfect flowers, staminate flowers only,
pistillate flowers only, or both staminate and pistillate flowers.
- in loose clusters, a
irregular in shape, up to 10 cm long,
arising from the leaf axils;
- often dioecious;
- about 1/8 inch in diameter;
- with five spreading to reflexed
petals about 1.5 mm long and 1 mm wide, off-white with a yellowish or
- with five green sepals;
- the staminate flowers with 5
stamens alternating with the petals;
- the pistillate flowers with a
with a stout style,
with whitish to yellowish stigmas;
- blooming for about 3 weeks, in June in my are, 25 km North of Montréal.
The fruits persist on the plant through winter and
are a favorite winter food of some birds despite their toxicity..
- grayish-white, hard dry drupes
with a waxy appearance.
- about 1/8 inch in diameter;
- containing a single seed.
Toxicodendron radicans is normally found in wooded areas, especially
along edge areas. It also grows in exposed rocky areas and in open fields and
disturbed areas. It also grows as a forest understory plant, although it is
only somewhat shade tolerant.
It is also common around lakes, swamps, and rivers.
It is not particularly sensitive to soil moisture, and is not
n indicator or uniquely associated with a particular
community type, although it does not grow in
desert or arid conditions. It grows in a wide variety of soil types, and soil
pH from 6.0 (acidic) to 7.9 (moderately
alkaline); It can grow in areas subject
to seasonal flooding or brackish water.
Toxicodendron radicans grows throughout much of the eastern half of
North America, including several states west of the Mississippi river,
including several Canadian provinces. The plant is extremely common in
suburban and exurban areas of New England, the Mid-Atlantic and Southeastern
United States. The plant is also found in the Russian Far East: Kurile Islands
and Sakhalin, in China, Japan and Taiwan. The plant has been
introduced in Europe (as a revenge for some
insult ?) The map shows the Canadian provinces and U.S.A. states where
the plant can be found.
Toxicodendron radicans is the most common of the urushiol producing
plants in the North America. Contact with urushiol oil is the substance
that causes an allergic rash in 85 to 90 % of the population.
Even a tiny amount (1 nanogram, a billionth of a gram) of sticky, resin-like
urushiol oil will case a skin reaction. 1/4 ounce of the potent oil would be
enough to cause a rash on the entire population of the earth!
Poison Ivy Facts:
The only sure way to avoid poison ivy rash is avoiding contact with urushiol
oil directly from the plant or indirectly from clothing, tools, or gear that
comes into contact with the oil.
- One must come into direct contact with urushiol oil to get the rash.
- Urushiol oil can be spread in smoke from burning plants and debris
from lawnmowers or trimmers.
- Urushiol oil is still present in dead plants or vines and remains
active for five or more years.
- Scratching the rash will not spread the rash (unless the oil is still
on the skin)
- Fluid from the blisters will not spread the rash.
- Sensitivity to urushiol oil can develop at any time.
- Depending on individual reactions to urushiol oil can appear in hours
Within fifteen minutes of exposure urushiol oil bonds with the skin and a rash
is likely. A long rinsing wash with cold water is an effective way to remove
the oil. Warm water opens the pores allowing more oil to bond with the skin and
soap may spread the oil more effectively.
Animals generally are not susceptible to dermatitis induced by
Toxicodendron radicans. It is an important winter food for
(White-tailed deer). The foliage, branches, and fruit are eaten by the
Ursus americanus (Black Bear), and
A wide variety of migrant and
resident non game and upland game birds consume the fruits in fall and winter.
Genera of the Picidae family
(Woodpeckers and Flickers) are especially attracted to the fruit.
In spite of its toxicity, Toxicodendron radicans was used by several
American native tribes. The Houmas took a decoction of leaves as a tonic.
The Algonquins of Québec are said to have rubbed the leaves on the skin
affected by a reaction to Toxicodendron radicans (increasing the
problem ?). The Cherokees used as decoction of the plant as an
emetic. The Kiowas used the plant to heal
running or non-healing sores; they rubbed the leaves over
boils or skin eruptions (making them worse ?)
The Navajos used the plant to poison arrows and chewed the leaves to insure
good luck in gambling !
The photos of the gallery were taken either with one of the following:
Minolta DiMAGE 7, Canon PowerShot A530,
Canon Xt Rebel, usually with the EF-S60mm f/2.8 Macro USM objective,
Fujifilm A 610 and EPSON Perfection 1650 (scanner).
The title in the window shows the date when the picture was taken,
i.e. jan_30_06... would mean that the photo was taken on the 30th of
January, the 06 is for the 6th picture taken that day.
The month, day and picture number might be followed by a letter which I use
to identify the system used to take the picture.
Click on the thumbnails to get larger view.
The original photos are usually in TIFF format,
the photos shown are generally in JPEG format,
often of dimensions one half (surface one quarter)
for loading time reduction.
The leaf and folioles were scanned at 300 dpi,
and the dimensions of the resulting picture divided by 2 (area divided by 4);
this allows to measure the dimensions of the leaves.