Monday, June 17, 2013

Native Species Profile - Common Milkweed

Last Friday, I posted some photographs taken in the field behind our office.  In two of those photographs a native species of plant featured prominently - the Common Milkweed (Asclepias syriaca).

Common Milkweed (Asclepias syriaca) - a view from ground level

Common Milkweed (Asclepias syriaca)

The Common Milkweed is well known as the host plant for the Monarch Butterfly .  I have already written a fair amount about the Monarch (Danaus plexippus) on previous posts about host plants, mimicry, and Monarch Waystations.  Due to severe declines in Monarch Butterfly populations there are several big campaigns (Bring Back the Monarchs, Wild for Monarchs, etc.) right now to educate the public on the needs of monarchs and to encourage people to plant gardens that include milkweed species. 

Early instar Monarch caterpillar - note the later instar caterpillar on the opposite side of the leaf

Fifth instar Monarch caterpillar on Common Milkweed

In Mid-Michigan, not surprisingly, the most common species of Milkweed found is the Common Milkweed.  The Common Milkweed is widely distributed throughout eastern North America.  It can survive in a variety of soil types and conditions, but thrives best in moist loam or sandy loam soils.  It grows in prairies, woodland openings, old fields, roadsides.  Common Milkweed is often found growing as a weed in agricultural fields.

The Common Milkweed is a very showy plant.  It can typically reach heights between 2 and 6 foot tall.  Its large leaves (and stems) are covered with downy hairs.  Its pink to purple flowers are clustered into a round globe that is 2 to 4 inches in diameter.  Each individual flower in the cluster has five petals.  The plant is a very popular nectar source for many species of insects including butterflies, moths, wasps, bees, and beetles.
The Common Milkweed can be found blooming from June into August (possibly September).

Common Milkweed inflorescence

Monarch Butterfly nectaring on a Common Milkweed

Skipper (unidentified) nectaring on Common Milkweed

After pollination, the Common Milkweed seeds develop in large fleshy pods.  Each large seed is attached to a tuft of silken hairs.  When the ripen the pod splits open and the seeds are carried away on the wind, buoyed by their tuft of hairs.  The seeds are often carried a great distance from the parent plant, starting new colonies.

Common Milkweed seeds

Common Milkweed pod and seeds

The Common Milkweed derives its name from its milky white sap.  This sticky, latex-like sap is one of several defenses that the plant uses to deter insects and other herbivores from consuming the plant.  The sap gums up the mouthparts of many insects.  It also contains cardiac glycoside chemicals (among other chemicals) that give the plant a bitter taste.  Consumption of large quantities of this chemical can result in vomiting and weakness - most herbivores avoid consuming this plant in any but small quantities.  The Monarch Butterfly and other insects that have co-evolved with the plant store these chemical in their bodies and use them to deter potential predators.  Most of these insects are brightly colored to warm predators of their toxicity.

This patch of Common Milkweed at Fayette State Park had a large number of Monarch Butterflies nectaring on it.  At least three of the Monarchs are visible in this photograph.

The Common Milkweed should be a favorite among gardeners.  It is large and showy with interesting foliage, produces large blooms that attract many pollinators, and deters herbivores.  These are all properties that many gardeners look for in flowers.  However, its tendency to look weedy after blooming means that many people do not want it.  Also the seeds often spread and grow in unwanted places - the seeds can be controlled by removing the pods before they are ripe.  Another point against the Common Milkweed is the fact that the plant produces not only by seed but also by sending out lateral roots that grow clones of the parent plant - often some distance from the original plant.  This can be controlled by planting it in a confined area.  But perhaps the biggest detriment to the Common Milkweed is its name - most gardeners do not want with common weed in its name in their gardens. 

If you have the undeveloped spaces please let this plant grow. In Mid-Michigan, many people will let it flower and then trim it down in the beginning of August to prevent it from spreading seeds. This is one of the worst things that you can do.  Around here that is the time when Monarch females are laying the eggs for the generation of butterflies that will migrate to Mexico.  By cutting the plants at this time, people are removing them when they are needed by the butterflies the most.  A better solution is to trim of the plants closer to the beginning of July, they will regenerate with fresh tender growth and be available for that lat generation of caterpillars.

Basic Information

Common Milkweed 
Asclepias syriaca

Height:  2-6’ tall

Habitat:  wet and dry fields, meadows, roadsides

Flower Color:  pink to purple

Bloom Time:  June – August

1 comment:

  1. I love this! I'm writing a paper on Asclepias syriaca, thanks for all the great info and visuals.