Ontario Weeds: Common milkweed
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Excerpt from Publication 505, Ontario Weeds,
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Table of Contents
- Name
- Other Names
- Family
- General Description
- Stems and Roots
- Flowers and Fruit
- Habitat
- Similar Species
- Caution
- Related Links
Name: Common milkweed, Asclepias
syriaca L.,
Other Names: asclépiade de Syrie,
cotonnier, petit-cochon
Family: Milkweed Family (Asclepiadaceae)
General Description: Perennial, reproducing
by seed and by horizontally spreading underground roots which produce
new leafy stems.
Common milkweed. A. Top of flowering plant. B. Seedpods with 1 open and showing its layers of seeds with their tufts of long silky hairs.
Stems & Roots: Stems erect, 1-2m
(3-6½ft) high, stout, unbranched or sometimes with 1 or 2
branches near the top, usually several stems close together from
the underground root system; leaves opposite (2 per node) or whorled
(3 or more per node), oblong with a rounded or tapered base and
a rounded to somewhat pointed tip, without teeth, underside covered
with fine velvety hair, upper surface usually without hair and deeper
green.
Flowers & Fruit: Flowers in dense,
nearly spherical clusters or umbels at tip of stem and from axils
of upper leaves, each flower 8-10mm (¼-2/5in.) across, greenish
to purplish or whitish, with 5 thin sepals and 5 larger petal lobes
bent back along the flower stalk and an unusual arrangement of 5
hoods and horns forming a crown or corona around the top of each
flower. The flowers are uniquely adapted for insect pollination,
having waxy pollen in tiny wishbone-shaped structures which hook
onto an insect's leg but come off when transferred to the flower
of a different plant. Fruits at first green, fleshy, 7-10cm (2½-4in.)
long and ¼ to ½ as wide, covered with soft, warty
protuberances, later turning brown, splitting lengthwise along a
single opening and releasing numerous seeds; usually only 1 or 2
(rarely up to 5) seedpods develop from the many flowers of a single
flower cluster; seed flat, oval, with a tuft of long silky hair
at one end. The whole plant, root, stem, leaves, flowers and fruit,
contain abundant, thick, white, milky juice. Flowers from mid-June
to August, and matures seed from August to October.
Habitat: Common milkweed occurs throughout
southern Ontario in pastures, meadows, waste places, roadsides and
cultivated land. It is especially common in the Manitoulin Islands
and the east-central portions of southern Ontario, but it seems
to be increasing in most other portions of the province as well.
Similar Species: It is distinguished by its pairs of broad, oval, softly hairy leaves, umbels of purplish to whitish flowers with their peculiar arrangement of parts, and the large, thick, softly warty seedpods.
Caution: Other species of milkweed have been found to be highly toxic to livestock, and circumstantial evidence suggests Common milkweed may, under some circumstances, also be toxic.
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
For more information:
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