|THE METROPOLITAN NATURALIST
|Common Milkweed (Asclepias syriaca)
The Common Milkweed grows to about five or six feet tall on roadsides, fields, and other
sunny areas. If any part of the plant is broken (leaf, stem, seedpod, etc.) a thick milky sap
oozes from it. The stem is upright and unbranched. Clusters of flowers in summer are
usually some shade of red or purple. In late summer and through the winter, warty seed
pods filled with tufted downy seeds replace the flowers. When the seed pods ripen and
break open, the seeds are carried by the wind on their silky tufts. The silky tufts of the
seeds are called "floss".
Very young Milkweed shoots or the young seedpods before the silky hairs develop inside can be eaten as a cooked
vegetable. The plant is very bitter, but by changing the water two times during cooking the bitterness can be
removed. The bitterness might also be removed by rinsing the shoots or seedpods three times with boiling water
When collecting young shoots is important to be sure of the identity. Dogbane (Apocynum sp.) shoots look very
similar and also have a milky sap. Dogbane and Milkweed often grow side be side. Other similar looking plants do
not have milky sap.
Some other species of Milkweed are poisonous, containing higher concentrations of cardiac toxins, called
cardenolides, than the Common Milkweed.
If you look closely at a Milkweed plant you might find some colorful insects feeding on the seedpods and leaves.
These insects are thought to acquire the bitterness of the plant they feed on, making them unpalatable to birds
or other predators. They also concentrate toxins found in low concentrations in the plant.
Some of the insects you might see are the Milkweed Bug (Oncopeltus fasciatus), the Monarch Butterfly (Danaus
plexippus) caterpillar, and the Milkweed Tussock Moth (Euchaetes egle) caterpillar. In the picture below, the
small red bugs are Milkweed Bug nymphs feeding on a young seedpod.
The Monarch caterpillar has been found to concentrate cardenolides found in relatively low concentrations in the
Common Milkweed. In fact, the concentration of cardenolides in Monarchs feeding on Common Milkweed may be
as high as in Monarchs that feed on poisonous species of Milkweed. The concentrated cardenolides might be
poisonous, or at least have unpleasant effects, for birds that happen to eat them. The bright orange and black
colors of these insects that feed on Milkweed are thought to be warning coloration to let predators know that
they are not edible.
See http://www.monarchlab.org/Lab/Research/Topics/Milkweed/Default.aspx for more on Monarch Butterflies and
The floss from ripe seeds may be used as a substitute for down as a stuffing and insulation for pillows and
|Chemical structure of Cardenolide.
Cardiac toxins found in milkweed are known as cardenolides because they
contain this structure. Monarch butterflies and other milkweed eating insects
accumulate these toxins to protect them from predators.