Monday, March 21, 2011

What is this? Milkweed or Just a Weed?

Can anyone help me identify this plant in my backyard prairie?

It is a volunteer plant that first appeared in my garden two years ago. Until this year, it was well behaved, but now new plants are sprouting up from the roots 3-4 feet from the original plant. The plant has not produced any flowers. 

I did not remove the plant when it was small because I thought it could be a milkweed. It  has several features that look like milkweed to this amateur botanist. The leaves look very similar to milkweed leaves. It has a milky sap like milkweed. It has never had aphids like most milkweed, although the nearby butterfly weed,  Asclepias tuberosa,  and green milkweed, Asclepias virdis, were covered in aphids last year. Some caterpillars fed on the mystery plant last year, but not monarch or queen. The caterpillars eventually turned into plain little brown moths.

Based on pictures I found online, I am wondering if this could be common milkweed, Asclepias syriaca, or prairie milkweed, Asclepias sullivantii. If this is  a variety of milkweed, it would be nice to have around for the monarchs, but it may turn out to be too aggressive for my garden. If this is not milkweed or another valuable wildlife plant, I need to act fast to remove the plant before it takes over my garden.

Here is a picture of the plant from July 23, 2010. It has some damage from the caterpillars.

Here is a shot of one of the caterpillars.

I will be posting my question on the Dallas Butterflies and Native Plant Society of Texas groups on Yahoo. I will also check with the Texas Butterfly Ranch blog to see if anyone can help. Any suggestions are welcome.

Update: the caterpillar is that of the Dogbane Saucrobotys Moth. This moth does eat milkweed, so maybe, just maybe, it is a milkweed. Fingers crossed and waiting for flowers or monarch caterpillars. Otherwise, I have some plant eradication to do.


  1. Pretty positive it's Asclepias sullivantii, "Prairie Milkweed".

  2. Quacks like milkweed, but must be low on the monarch/queen food totem if you didn't see any cats on it.

  3. Kathleen, it is rare that I get monarch caterpillars. I get a few butterflies that pass through in the spring and act like they are laying eggs, but only a couple of times have there been caterpillars. I would settle for aphids if it would help me identify the plant before it takes over. Aphids are a sure quack for milkweed.

    I hope you are right mdutch. A couple of people on the Dallas Butterflies Yahoo group suggested dogbane. This is a plant I considered too. They look very similar. Dogbane can be attractive, but it is known for being invasive too.

    Bugguide says that the caterpillars feed on both milkweed and dogbane. Do you know if it has a solid stem? I understand that dogbane has a solid stem, not hollow. I'll share your blog with others. I know someone will know more than I do! ~Edith (Shady Oak Butterfly Farm)

  5. The leaf shape indicates that it may be Asclepias viridis. Flowers of viridis are pale green. The gynostegium would be pale purplish rose.
    (Gynostegium: the disk or columnar structure of Milkweed made up of the connate stamens, style, and stigma.)
    Botanical Illustrator

  6. Don't know what the plant is, but it sure is pretty. Hope it turns out to be milkweed. Great photos!

  7. Definitely a milkweed. Hard to know which without a photo of the flowers. You are doing amazing things there in Plano, bravo to you!! Yay!

  8. Milkweeds except A. tuberosa have a milky "sap" which contains cardiac glycosides and your plants have a milky latex.
    "I am wondering if this could be common milkweed, Asclepias syriaca, or prairie milkweed, Asclepias sullivantii."
    It would be unlikely to find these in Plano. They are not listed in "Illustrated Flora of North Central Texas."
    If it were a milkweed, you would have seen milkweed flowers and seedpods
    Do you have snow-on-the-prairie (a Euphorbia)?
    It also contains a milky latex.
    I think that it is most likely dogbane which also contains a cardiac glycoside. Check "Illustrated Flora of North Central Texas."

  9. Thanks to everyone for your input. I will keep the mystery plant around a little longer. Maybe the plants will get aphids, monarch caterpillars, or flowers to help with the identification. I am leaning toward identifying the plant as dogbane.

  10. Update us when you find out if your plant is milkweed, please!

  11. Edith, I think everyone that thought it was dogbane was probably correct. Monarchs always passed over it and went straight to the plants that I knew for sure were milkweed. Besides that, it began spreading aggressively which is not allowed in my garden. I dug it out as best I could, but it kept popping up everywhere all summer long. I am sure I will have to stay on top of it next summer as well.

  12. This is long since passed but the branching in your later photos gives it away as dogbane. Asclepias rarely, if ever, branch. Good deduction skills, everyone!


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