Cirsium undulatum

{{Short description|Species of thistle}}

{{Speciesbox

| image = Cirsiumundulatum.jpg

| status = {{TNCStatus}}

| status_system = TNC

| genus = Cirsium

| species = undulatum

| authority = (Nutt.) Spreng.

| synonyms_ref = [http://www.theplantlist.org/tpl1.1/record/gcc-91822 The Plant List, Cirsium undulatum (Nutt.) Spreng. ]

| synonyms =

• Carduus megacephalus A.Nelson
• Carduus undulatus Nutt.
• Cirsium megacephalum (A.Gray) Cockerell ex Daniels
• Cnicus undulatus (Nutt.) A.Gray

}}

Cirsium undulatum is a species of thistle known by the common names wavyleaf thistle and gray thistle.[http://www.calflora.org/cgi-bin/species_query.cgi?where-calrecnum=2150 Calflora taxon report, University of California, Cirsium undulatum (Nutt.) Spreng., wavy leaved thistle, wavyleaf thistle ] It is native to much of central and western North America from British Columbia east to Manitoba and south as far as the State of Durango in Mexico. It has also been found outside of its native range as an introduced species.[http://bonap.net/MapGallery/County/Cirsium%20undulatum.png Biota of North America Program 2014 county distribution map]

Cirsium undulatum is widespread and found in many habitat types. It is a perennial herb exceeding {{convert|200|cm|in|abbr=on}} in height. The stem branches a few times toward the top of the plant if at all. The leaves are very wavy along the edges and usually cut into shallow toothed lobes. The longest near the base of the plant are up to {{convert|30|cm|in|abbr=off}} long. The inflorescence holds one or more flower heads each up to {{convert|5|cm|in|abbr=off}} long and wide. The head is lined with spiny phyllaries of different shapes. The flowers in the head are white to lavender to pink and up to {{convert|5|cm|in|abbr=off}} long. The fruit is an achene a few millimeters long with a pappus which may be up to 4 centimeters in length.[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242416297 Flora of North America, Cirsium undulatum][http://plants.usda.gov/java/profile?symbol=CIUN United States Department of Agriculture Plants Profile]

Cirsium undulatum has been shown to have its seed production reduced by an exotic weevil Larinus planus which was released to control Canada thistle.{{cite journal |last1=Louda |first1=Svaa M. |last2=O'Brien |first2=Charles W. |title=Unexpected Ecological Effects of Distributing the Exotic Weevil, Larinus planus (F.), for the Biological Control of Canada Thistle |journal=Conservation Biology |date=June 2002 |volume=16 |issue=3 |pages=717–727 |doi=10.1046/j.1523-1739.2002.00541.x |url=http://web.wits.ac.za/NR/rdonlyres/CD7EB87D-64DC-419C-95BA-2F1A7E60329D/0/LoudaandOBrien2002.pdf }}{{Dead link|date=July 2019 |bot=InternetArchiveBot |fix-attempted=yes }}