Ontario Weeds: Common milkweed
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.
Photos and Pictures
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
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