Habitat Preferences: Widely distributed in disturbed open sites, roadsides, pastures, annual grasslands, and waste areas.
Recorded Range:Carduus pycnocephalus is an invasive species in the United States in: AL, AR, CA, ID, NY, OR, SC, TX, WA. It is native to the Mediterranean region and some other countries further north or east.
U.S. Weed Information: In North America Carduus pycnocephalus, Italian thistle; compact-headed thistle can be weedy or invasive according to the following authoritative sources: State noxious weed lists for 46 states; California Invasive Plant Council; Weeds of the West. Plants included here may become weedy or invasive.
Invasive/Noxious Weed Information: In North America species is listed as a Noxious Weed by the federal government and/or a State; Arkansas, Carduus thistle, Noxious weed; California, Italian thistle C list (noxious weeds); Iowa, Carduus thistle, Primary noxious weed; Oregon, Italian thistle "B" designated weed, Italian thistle, Quarantine; Washington, Italian thistle Class A noxious weed, Italian thistle Noxious weed seed and plant quarantine. Plants included here are invasive or noxious.
Carduus pycnocephalus has become a noxious weed in Australia, New Zealand, Macaronesia, South Africa, the Arabian Peninsula, South America, Hawaii, and North America.
Wetland Indicator: No information available.
Threatened/Endangered Information: No information available.
Genus Information: In North America there are 6 species and 6 accepted taxa overall for Carduus. Worldwide, The Plant List includes 130 accepted species names and a further 297 scientific names of infraspecific rank for Carduus.
In the Southwestern United States: Arizona has 6 species of genus Carduus, California has 10 species, Nevada has 7 species, New Mexico and Utah each have 9 species, Texas has 13 species. All data approximate and subject to revision.
There are 2 sub-species in Carduus pycnocephalus, 1 in the United States;
Carduus pycnocephalus subsp. pycnocephalus.
Comments:Carduus pycnocephalus is introduced in North America and has become an introduced species in other regions around the world, often becoming a noxious weed or invasive species. This species grows densely, crowding out other vegetation and competing with native species. Its ability to grow in dense stands increases the risk of wildfire.
Importance to Wildlife, Birds and Livestock
Carduus pycnocephalus is an invasive species which spreads rapidly and forms dense stands in pastures and rangeland likely crowding out desirable forage for wildlife species and livestock. Additionally, animals do not like to forage on it because its foliage is so spiny. Birds and small mammals including bats may likely feed on the small seeds and what nectar that might be available.
Special Value to Native Bees, Butterflies and Insects
The genus Carduus is the Latin name for "thistle" or "thistle-like plant". The genus Carduus was published by Carl Linnaeus in 1753.
The species epithet "pycnocephalus" means "thick-headed", with heads in thick clusters.