En EspaŅol

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
1 rating

Wednesday - March 13, 2013

From: San Marcos, TX
Region: Southwest
Topic: Non-Natives, Plant Identification, Herbs/Forbs
Title: How to tell the difference between native and non-native thistles
Answered by: Nan Hampton


It's thistle time already. There are many plants in the aster family with thistle in their common name. Are "real" thistles only those in the genus Cirsium, or are there others as well? We are trying to learn how to identify non-native thistles before they bloom without disturbing our natives. Any hints on differences (other than flowers) would be welcome. Thanks.


There are several native plants that have "thistle" as part of their names (e.g., Argemone polyanthemos (Thistle poppy or Annual pricklepoppy) in the Family Papaveraceae (Poppy Family) and  Eryngium heterophyllum (Mexican thistle) in the Family Apiaceae (Carrot Family); but, as you mentioned Cirsium in the Family Asteraceae (Aster Family) is the major genus of what are generally thought of as native thistles in North America. The basal rosettes and general leaf morphology are the features to use for identifying which are native and which are non-native before they flower.  The ones that occur in Hays County or in adjacent counties are:

  • Cirsium horridulum (Yellow thistle), despite its unfortunate species name, is a native of Central Texas.  The flower color can be pink, yellow or white.  You can see more photos and information as well as a photo of the basal rosette of a young plant at Natives for Your Neighborhood from the Institute for Regional Conservation in South Florida. You can read a detailed botanical description from eFloras.org (the online version of the Flora of North America). 
  • Cirsium texanum (Texas thistle) occurs over nearly all of Texas with the exception of the Panhandle, far West Texas and East Texas bordering Louisiana. You can see a photo of a basal rosette of a young plant on Dave's Garden page and here are photos and more information from the University of Texas Biological Sciences' Archive of Central Texas Plant Species. You can read a detailed botanical description from eFloras.org (the online version of the Flora of North America). 

The only non-native Cirsium you are likely to find in Hays County is Cirsium vulgare (bull thistle).  You can see a photo of the basal rosette of a young plant at New Mexico Weed Information database and more photos from the Virginia Tech Weed Identification Guide.  You can read a detailed botanical description from eFloras.org (the online version of the Flora of North America).

There are a couple of species occurring in or near Hays County that are in the Genus Centaurea

Carduus is genus of thistles that are all introduced from Europe, Asia or North Africa. 

  • The species of Carduus that you are most likely to see in or around San Marcos and Hays County, Texas is Carduus tenuiflorus.  You can see more photos from CalPhotos Berkeley. If you click on Texas on the distribution map on the species page in the USDA Plants Database, you will get a county distribution map of Texas to see that it has been reported in Travis County.  

Silybum marianum (Blessed milkthistle) is another species of thistle from Europe and Asia that has been reported in Hays County. Its seeds have been used as herbal medicines since ancient times to treat liver diseases and other ailments.  Its leaves and basal rosette are easily identified since they have white net-like lines on them.

There are a couple of other non-native members of the Family Asteraceae that are called thistles that occur in Hays County:

Finally, there are a couple of plants in the Family Apiaceae (Carrot Family) that don't have the common name of thistle, but do look very much like thistles.  They both are native and occur in or adjacent to Hays County:

Eryngium leavenworthii (Leavenworth's eryngo) occurs in Hays County and Eryngium hookeri (Hooker's eryngo) occurs in Travis County.

Below are photos from our Image Gallery of the thistle or thistle-like species native to Central Texas.


From the Image Gallery

Yellow thistle
Cirsium horridulum

Yellow thistle
Cirsium horridulum

Yellowspine thistle
Cirsium ochrocentrum

Texas thistle
Cirsium texanum

Wavyleaf thistle
Cirsium undulatum

American basket-flower
Centaurea americana

Leavenworth's eryngo
Eryngium leavenworthii

Hooker's eryngo
Eryngium hookeri

More Non-Natives Questions

Non-native mimosa failing to bloom in Leitchfield KY
October 29, 2011 - I have a medium size mimosa tree here in KY that usually blooms beautifully; it did not bloom at all this year. It leafed out well, needs a few dead limbs pruned, but seems otherwise healthy. Please t...
view the full question and answer

Type of non-native parsley for swallowtails from Austin
September 02, 2012 - What is the best type of parsley for Yellow Swallowtails? Lost a caterpillar when it ran out of food from a parsley plant. I can't remember what kind of parsley. It would not feed on Rue, cilantro...
view the full question and answer

Gaura dying from Townsville, Australia
September 14, 2012 - My passionate pink Gaura appears to be dying. It had a beautiful blooming period & now is going backwards. What is happening? I have pruned it, but don't know how to save it.
view the full question and answer

Wound from non-native date palm thorn Naples FL
November 12, 2012 - Was trimming my pygmy date palm when a frond fell and a thorn pierced my rubber gloves and stuck me in the web of skin between my thumb and forefinger. Did not see a broken thorn but area where struc...
view the full question and answer

Non-native, invasive, poisonous Chinese yam
October 16, 2005 - I found a vine in my yard [central Indiana] which I believe is Dioscorea oppositiflora and I wanted first to confirm my identification and second to find out about edibility [especially of the airborn...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2015 Lady Bird Johnson Wildflower Center