Milkweed Plant Identification Help

Can You Identify These Milkweed Impostors?

Recently I posted about strange brown globes attached to my common milkweed. Thanks to your comments, I discovered the true identity of those foreign milkweed objects.

A few days later, I stumbled across another perplexing milkweed mystery. A Florida gardener sent me a milkweed plant identification request wondering was this showy milkweed…or perhaps the plantabulous purple milkweed variety?

Over the 4th of July, I saw these same plants on a city boulevard in Chicago. After seeing them up close and personal, I was pretty sure they weren’t a perennial milkweed species I was familiar with…but I left the windy city without making a positive ID.

Now, I’ve discovered a familiar ‘swampostor’ blending in with our swamp milkweed patch. But this time the faux milkweed made a fatal mistake. The cascading flowers clearly revealed its family secret…milkweed is not the father!

Milkweed Impostor! Get to know this plant, often mistaken for milkweed, so you don't accidentally try feeding it to hungry monarch caterpillars...
Not Milkweed Flowers

The leaves look like a cross between swamp milkweed and tropical milkweed, but with deeper veins. The stalks of the plants look more like tropical milkweed.

Do You Recognize The Milkweed Impostor attempting to blend in to the swamp milkweed patch? This plant is not butterfly food for munching monarch caterpillars...

Before I saw its flowers, I was wondering if this mystery plant could be the result of cross-pollination between swamp/tropical milkweed. After the blooms were revealed, I realized there was a milkweed impostor in our midst…

Update: Thanks to everyone who contacted me about this milkweed mystery. The general consensus is that this is some type of Persicaria (formerly Polygonum) species. To me, it most resembles Persicaria hydropiperoides, aka swamp smartweed…Mystery solved!

Milkweed Impostor 2

This July, a second milkweed impostor has been discovered in the swamp milkweed patch. It also has leaves resembling Asclepias incarnata, but its flowing purple panicles have revealed it as a milkweed brother from another mother:

Two common mystery milkweed impostors and the helpful plant identification tool you can use to ID mystery plants in your garden

This season I turned to a new ally in my question for plant identification:

Plant Identification Facebook Group

A helpful group member had my answer within a matter of minutes:

Lythrum salicaria (purple loosestrife)

After further research I discovered this plant is classified as a noxious weed in our state, so I dug it out and put it in the yard waste can.

Another milkweed mystery solved… 

Milkweed Impostor 3

Dogbane is another plant that people often mistake for milkweed, as its leaves bear a close resemblance to common milkweed.

When comparing plants that look like milkweed, dogbane probably fools the most people into thinking they’ve found the common milkweed jackpot, but dogbane is not a viable option for hungry monarch caterpillars to feed on.

Ironically, another milkweed caterpillar, the tussock moth caterpillar is able to grow through its life cycle eating dogbane leaves…go figure!

So what is the difference between milkweed and dogbane?

Asclepias syriaca grows from a single green stem, while dogbane grows on multiple, often-reddish stems:

plants that look like milkweed dogbane plant identification
Milkweed? Look closer…

Common Milkweed typically blooms earlier in the season and has showier blooms:

Common Milkweed Blooms
Bursting Blooms of Common Milkweed

In August and September, common milkweed plants are easy to distinguish with fat seed pods, while dogbane pods are long and slender.

Both milkweed and dogbane contain milky sap so don’t try to ID that way!

I hope you’ve found these milkweed plant identification tips helpful. If you know other plants that look like a species of milkweed and how to tell the difference, post in the comment section below…

Click the following link to find 30 REAL Milkweed Varieties for monarch butterflies and your butterfly garden.

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  1. Is smartweed beneficial for polinators and worth having in the garden? Like a wildflower garden.

  2. Hello- I noticed a long crawling vine on an evergreen shrub in front of the house, and also noticed a couple of Monarch butterflies on the vine. I feel sure the vine is some type of invasive weed, however, it has little flowers which look a lot like Milkweed flowers. Now, I am seeing two beautiful Monarch caterpillars eating away on just the leaves of this vine. The vine is also full of tiny yellow aphids. Lots on both the stem and leaves of this vine. My husband and I ordered Ladybugs which should arrive soon, I was planning to release the Ladybugs on the vine to get rid of the aphids, is this OK?

    1. Hi Ruth, ladybugs will eat small caterpillars too…if you release them on the honeyvine, I would remove eggs/caterpillars first

    1. Hi Lisa, thanks for posting this. From all the feedback I’ve been getting, I’m confident it’s some sort of Polygonum (smartweed). This seems to be a likely possibility. It’s also commonly found in Minnesota.

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