‘Swamp milkweed’ purchased at May 6 plant sale in Prince Frederick

Question: Good Morning 
I purchased 4 plants labeled as swamp milkweed at the spring Prince Frederick plant sale. After growing through this season, they seem to be a different type of milkweed. These plants are have grown taller compared to my previously planted swamp milkweeds and have white flowers. I’m concerned that I have introduced a non-native milkweed into the garden. Any thoughts on what type of milkweed these are and if they are appropriate for this area?  Thanks

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 03, 2023, 10:49 AM EDT
response: Yes, we would agree that this does not appear to be a native cultivar of the white blooming  Swamp milkweed (Asclepias incarnata 'Ice Ballet' ) and possibly is a plant species that is native to South Africa/New Zealand: Gomphocarpus fruticosus or physocarpus (Swan Flower or Balloonflower). While they are not native here they do not appear to be invasive since they are more a zone 10 plant and would have a difficult time surviving our winters. Of course there is the possibility of the seeds spreading and overwintering though in mild winters. You could wait to see if it blooms and forms seed pods because you will be able to tell for sure from those. If you don't want to risk it going to seed and and potentially spreading, you can remove it before seed dispersal. It wouldn't harm pollinators though and may still attract butterfly species.  This is the native species of Swamp Milkweed with the pink blooms: https://www.marylandbiodiversity.com/view/142 You can compare the seed pods and blooms with the photos of seed pods of the Swan or Balloonflower plants.  If you decide to let it continue growing and develop the seed pods, feel free to send in photos of those at that time.  Let us know if you have further questions.  Emily

responder: The Question Asker Replied July 04, 2023, 9:04 PM EDT
response: Good Evening Emily et al.Thank you for the reply.  Since my initial message, some of the flowers have bloomed, and it does appear to be Gomphocarpus physocarpus.  I am attaching a picture of the flowers.  I’m also attaching a photo I took May6 after I left the plant sale.  In it, barely, you can see a marker that I believe says swamp milkweed.  I’m going to remove and destroy the plants based on this article I found on the monarchscience.org website.  https://www.monarchscience.org/single-post/is-swan-milkweed-hairy-balls-a-better-alternative-to-tropical-here-is-the-answer#:~:text=This%20species%2C%20called%20either%20swan,United%20States%20(and%20also%20a Thanks again so much for your help.Michelle On Jul 3, 2023, at 10:49 AM, Ask Extension <<personal data hidden>> wrote:﻿

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 06, 2023, 12:14 PM EDT
response: Hi Michelle,  We don't have a lot of information based on what was shared in that blog post but if you are concerned then probably best to remove.  It is possible that the plant was mislabeled as that can happen from time to time and many plants look so similar when they are young and before blooming.  Thanks for reaching out to us! Emily