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Mr. Smarty Plants - How Can I Tell an Invasive Thistle from a Native

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Tuesday - May 01, 2012

From: West Lake Hills, TX
Region: Southwest
Topic: Invasive Plants, Non-Natives, Plant Identification, Problem Plants
Title: How Can I Tell an Invasive Thistle from a Native
Answered by: Mike Tomme

QUESTION:

Mr Smarty Plants, I have some thistles coming up in my yard. I'd like to keep them if they are native, but not if they are invasive or non-native. How can I tell? My yard is a wild area in West Lake Hills, TX.

ANSWER:

It would seem you have asked a simple question, but in reality you haven't. As you can see from this previous Mr. Smarty Plants answer, there are quite a few different plants that occur in central Texas that can be called some sort of thistle. As this answer makes clear, it can be difficult to tell the natives and non-natives apart and it requires a fair amount of research.

To help simplify mattes, I am going to assume that the thistles in your yard are the ones with the pink/lavender flowers that are blooming all around central Texas at this time of year. If you have the ones with yellow or white flowers, go back to that previous answer.

In her book Wildflowers of Texas, Geyata Ajilvsgi includes two thistles with pink/lavender flowers which I take to mean they are among the most common. They are:

Cirsium texanum (Texas thistle) - As you would guess from its name, this is a native thistle

Carduus nutans (nodding thistle) - This is a non-native. It is listed as an invasive plant by both Texasinvasives.org and the USDA. Another common name for it is musk thistle.

These are very similar in appearance. I sought help with identification methods from Minette Marr at the lady Bird Johnson Wildflower Center and she suggested a article published by the Oklahoma Cooperative Extension Service at Oklahoma State University entitled Thistles in Oklahoma and Their Identification.

 

From the Image Gallery


Texas thistle
Cirsium texanum

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Bibliography

Wildflowers of Texas (2003) Ajilvsgi, Geyata.

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