Ontario Weeds: Poison ivy
Excerpt from Publication 505, Ontario Weeds,
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Table of Contents
- Other Names
- General Description
- Stems and Roots
- Flowers and Fruit
- Similar Species
- Related Links
Name: Poison-ivy, Rhus radicans
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.
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
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.
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