Ontario Weeds: Poison
ivy
Table of Contents
- Name
- Other Names
- Family
- General Description
- Stems and Roots
- Flowers and Fruit
- Habitat
- Similar Species
- Caution
- Related Links
Name: Poison-ivy, Rhus radicans
L.,
Other Names: herbe à la puce,
sumac vénéneux, sumac grimpant, bois de chien; incorrectly
called Poison-oak which is Rhus toxicodendron L. and does
not occur in eastern Canada
Family: Cashew Family (Anacardiaceae)
General Description: Perennial, spreading
by seed and by woody rhizomes (underground stems) which produce
dense patches.
Photos and Pictures
|
Poison ivy. A. Low-growing form with short erect stem
and a flower cluster form the axil of 1 compound leaf.
B Cluster of dry white, berry-like fruits produced from
the flower cluster.
|
C-E. Variation in margin and lobing of leaflets. |
Stems & Roots: Stems woody and
of two kinds, the most frequent kind growing horizontally on or
just below the ground surface with upright leafy stalks 10-80 cm
(4-32 in.) high; the second kind is a climbing vine which develops
aerial roots and may climb 6-10 m per node, compound, each compound
leaf consisting of 3 leaflets at the tip of a long leafstalk (petiole);
the middle leaflet has a longer stalk than the 2 side leaflets;
overall leaflet shape and type of toothing highly variable between
leaflets on the same stem, as well as among plants within a patch
and between patches; leaflets ranging from narrow to broadly ovate
with a smooth margin, to a few scattered, shallow, rounded teeth,
to several, coarse, deep-pointed teeth which give the leaflet a
lobed appearance; leaves purplish to reddish when unfolding in spring
(May to early June), bright green and often shiny (with a varnished
appearance) in summer and turning a vivid orange-red to wine-red
in autumn in sunny areas, but often lacking the bright colour in
shaded places; leaflet smooth and hairless on both surfaces except
for small tufts of brownish hair on the underside along the mid-vein
and in the angles formed by the mid-vein and some of the lower branching
veins.
Flowers & Fruit: Flowers small,
white or greenish, with 5 sepals and 5 petals, in branching clusters
from the leaf axils (angles between leafstalk and stem); flower
clusters inconspicuous because they are often hidden below the dense
leaf canopy and because many plants do not flower every year; each
flower in the cluster followed by a whitish to dull greenish-yellow,
dry, berry-like fruit about 5 mm (1/5 in.) in diameter with lengthwise
ridges and somewhat resembling a peeled orange. Flowers in June
and July; berries produced by September but often remaining on the
low leafless stems all winter.
Habitat: Poison-ivy occurs under forests,
in edges of woodland, meadows, waste areas, fence lines, and roadsides
throughout most of Ontario south of a line from North Bay to Kenora.
The tall climbing vine form, however, is mainly confined to the
counties bordering Lake Erie, Lake Ontario and the lower Ottawa
Valley.
Similar Species: It is distinguished
by its low growth or its occasional climbing habit, its 3 leaflets
in each compound leaf, its leaves deep green in summer, reddish
in spring and fall, its clusters of whitish to greenish-yellow berries,
and its short, erect, leafless stems which frequently retain a few
berries all winter long. Poison-ivy is sometimes mistakenly called
Poison-oak because some plants have very coarsely toothed or lobed
leaflets. The true Poison-oak, Rhus toxicodendron L. (not
illustrated) [TOXQU] occurs in the southern United States, but not
in Canada.
| Caution: All parts of Poison-ivy,
including the roots, contain a poisonous substance which causes
an irritating inflammation of the skin of most people, the inflamed
areas frequently developing blisters and accompanied by intense
itchiness. The poisonous substance is an oily resin contained
in the juice of the plant. Contact with any broken part of the
plant, with leaves which have been chewed by insects, or with
shoes, clothing, implements, or pets which have touched broken
parts of the plant may cause a person with sensitive skin to
react. Dry twigs in winter or dug-up roots in summer can often
cause a reaction. Burning Poison-ivy leaves and stems releases
the poison in the form of tiny droplets on particles of ash
and dust in the smoke, and can cause a severe reaction on exposed
skin and in the breathing passages if a sensitive person breathes
or passes through the smoke of such a fire. The author had a
severe reaction on his arms and legs after trimming a specimen
plant with hand clippers. Although the plant parts never touched
his clothes, it seems that microscopic oil droplets may have
squirted out while cutting the stems and vines and penetrated
the cotton of his trouser legs and shirt sleeves. In cases of
suspected contact with the plant, washing the skin and clothing
with a strong soap may not prevent a reaction but it will help
minimize reinfection to other parts of the body or to other
individuals. If a reaction does develop, one should seek the
advice of a physician for proper treatment. Poison-ivy is designated
as a noxious weed by the Province of Ontario, and it is the
duty of every person in possession of infested land to destroy
noxious weeds thereon. |
Related Links
... on general Weed
topics
... on weed identification, order OMAFRA
Publication 505: Ontario Weeds
... on weed control, order OMAFRA
Publication 75: Guide To Weed Control
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to the Ontario Weeds Gallery |
