Cirsium arizonicum, Arizona Thistle
Scientific Name: Cirsium arizonicum
Common Name: Arizona Thistle
Also called: Spanish: Cardo Santo
Family: Asteraceae, Sunflower Family
Synonyms: (Cirsium arizonicum var. arizonicum, C. arizonicum var. nidulum, C. nidulum, Cnicus arizonicus)
Duration: Biennial or perennial.
Size: Up to 4 feet.
Growth Form: Subshrub; spiny all over, basal rosette with 1 or more stems, erect or ascending, tomentose or glabrous.
Leaves: Green; basal leaves 4 to 8 inches, some lobed, tomentose, spiny throughout, leaves variable, linear, elliptic or oblong, sharply toothed, upper leaves more glabrous, clasping, spines along margins.
Flower Color: Red, pink or purple disk flowers only; corollas tube shaped, 1 or several heads on short peduncles; bracts below flowers tipped with long spines not strongly reflexed; fruit is an achene.
Flowering Season: May to October.
Elevation: 3,000 to 7,000 feet.
Habitat Preferences: Upper deserts, pine, pinyon-juniper and chaparral communities, sunny open areas, woodland openings and rocky slopes.
Recorded Range: Arizona Thistle is found in the southwestern United States in AZ, CA, NM, NV and UT and in northwest Mexico. In Arizona, Arizona Thistle is found in higher elevations in the northern and southern parts of the state.
U.S. Weed Information: No data available.
Invasive/Noxious Weed Information: No data available.
Wetland Indicator: Cirsium arizonicum is on the USDA 2012 National Wetland Plant List.
Threatened/Endangered Information: No data available
Comments: Arizona Thistle characteristics are variable across their relatively wide geographic range and five varieties have been described.
Most southwestern native thistles are non-aggressive; non-invasive species that have evolved to thrive in select geographic southwestern ecosystems. With its bright red flowers and tubular corollas, Arizona Thistles are heavily visited by hummingbirds and, like most thistles, a variety of insects.
The genus Cirsium has achieved adverse notoriety from two introduced European thistles now wide-spread throughout North America; Canadian thistle, Cirsium arvense is listed as noxious in 33 states and Bull Thistle, Cirsium vulgare, is also a noxious weed.