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, Cirsium arizonicum var. nidulum, Cirsium nidulum, Cnicus arizonicus)
Duration: Perennial or biennial.
Size: Up to 4 feet (30-150-cm) or more in height.
Growth Form: Forb/herb; spiny all over, basal rosette with 1 or more stems, erect or ascending, tomentose or glabrous; stems woolly to cobwebby.
Leaves: Green; basal leaves sessile, 4 to 8 inches, some lobed, tomentose, spiny; cauline leaves alternate; leaf shape variable, linear, elliptic or oblong, sharply toothed, upper leaves more glabrous, clasping, spines along margins.
Flower Color: Red, pink, purple or lavender (rarely white); 1 to 100 erect heads; disk florets only; corolla tube shaped; phyllaries ovate or lanceolate; fruit is a cypsela often mistaken as an achene.
Flowering Season: May to October or November
Elevation: 3,000 to 12,000 feet (900-3,600 m)
Habitat Preferences: Sunny open areas, woodland openings and rocky slopes; wide variety of upland habitats; upper deserts, pine, pinyon-juniper and chaparral communities.
Recorded Range: Arizona Thistle is found in the southwestern United States in AZ, CA, NM, NV and UT. In Arizona, it is found in higher elevations in the northern and southern parts of the state. It is also native to northwest Mexico.
North America & US County Distribution Map for Cirsium arizonicum.
Threatened/Endangered Information: ∗Cirsium arizonicum var. tenuisectum, Desert Mountain Thistle is listed by California Rare Plant Rank: as 1B.2 Rare or endangered in California and elsewhere; .2: Fairly endangered in California
∗Note: This variety is Known in California only from the New York Mountains of San Bernardino County. The name Cirsium nidulum has long been misapplied to this species. May be distinctive enough to be its own taxon and not a variety of Cirsium arizonicum
U.S. Weed Information: No data available
Invasive/Noxious Weed Information: In North America the genus Cirsium is listed as a Noxious Weed by the States of Arkansas and Iowa. Plants included here are invasive or noxious. ∗ See Comments section below.
Wetland Indicator: In North America Cirsium arizonicum has the following wetland designations: Arid West, FACU; Great Plains and Western Mountains, Valleys, and Coast, FAC.
FAC = Facultative, occur in wetlands and non-wetlands
FACU = Facultative Upland, usually occur in non-wetlands, but may occur in wetlands
In the Southwestern United States: Arizona and New Mexico each have 19 species of genus, California has 27 species, Nevada has 16 species, Texas has 12 species, Utah has 23 species. All data approximate and subject to revision.
There are 5 varieties of Cirsium arizonicum in Flora of North America;
Cirsium arizonicum var. rothrockii, (AZ, NM);
Cirsium arizonicum var. arizonicum, (AZ, CA, NM, NV, UT);
Cirsium arizonicum var. chellyense, (AZ, NM)
Cirsium arizonicum var. bipinnatum, (AZ, NM, NV, UT);
Cirsium arizonicum var. tenuisectum, (CA, NV).
Comments: Arizona Thistle characteristics are variable across their relatively wide geographic range with five varieties having been described. This species is used to describe a complicated "complex of species and varieties".
∗The genus Cirsium has received adverse notoriety because of the introduction of two thistles native to Europe and now widespread throughout North America. The Canadian Thistle, Cirsium arvense and and the Bull Thistle, Cirsium vulgare are both listed as noxious primarily by agricultural interests.Most southwestern native thistles, including Arizona Thistle, are non-aggressive; non-invasive and beneficial as pollinators that have evolved to thrive without becoming weedy. Many native thistles are now threatened with some species at risk of extinction.
For excellent information on vertebrate conservation visit The Xerces Society.
The species epithet "arizonicum" is a direct reference meaning of or from or otherwise honoring Arizona.