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     There are several dozen Thistles, native and introduced, in the Four Corners area.   Some of these Thistles reproduce from rhizomes; others are biennial, reproducing from seeds.  All are spiny and have only disk flowers.  Most Thistles are large and obvious in plant and in flower.  Some non-native Thistle are serious invaders of meadows and pastures.  

    The genus name, "Cirsium", is Greek for "dilated vein" from the bygone belief that a Thistle distillate opens clogged veins.  

    Both Kartesz, the ultimate authority for all names on this web site, and the Flora of North America, accept Cirsium arizonicum as the name for the Thistle shown on this page. Colorado plant authority William Weber accepts C. calcareum.

     Here is what David Keil, Cirsium expert and the FNA Cirsium author, says about this species: "I have wrestled with how to treat these plants since beginning my research for ... [the FNA]. After careful consideration of the complex patterns of variation among members of the C. arizonicum complex, I acknowledged the futility of trying to distinguish more than one species. Any character combinations that I or others have attempted to use to distinguish species break down hopelessly when enough specimens are examined. Instead I have chosen to recognize that in this complex, as in several others, the plants in question are a work of evolution in progress. Cirsium arizonicum is a rapidly evolving, only partially differentiated assemblage of races that have not reached the level of stability that is usually associated with the concept of species".

Cirsium arizonicum
Cirsium arizonicum
Cirsium arizonicum variety bipinnatum.  Synonym: Cirsium calcareum.   (Arizona Thistle)
Asteraceae (Sunflower Family)

Foothills, montane. Woodlands, openings. Spring, summer.
Above: Knife Edge Trail, Mesa Verde National Park, June 21, 2015.
Left: Navajo Reservation near Teec Nos Pos, Arizona, June 24, 2006.

This compact, short thistle is a fortress of spines with a cylindrical flower head emerging from a pineapple-like bud. The pineapple appearance is due to the phyllaries, the whorl of triangular, overlapping bracts surrounding the base of the flower head. The plant grows in low Pinyon-Juniper forests, often in rocky areas.

In the above photograph, a Juniper Hairstreak (Callophrys gryneus) leisurely fed on the flower while I took photographs of it. The Juniper Hairstreak is common and widely distributed across the United States, but I had not previously noticed it.

The genus Cirsium was named by Philip Miller (1691-1771).  The species has had numerous names.  It was at first named Cnicus drummondii by Alice Eastwood in 1893 from a specimen she collected near present day Mesa Verde National Park.  It was renamed Cnicus calcareus by Marcus Jones in 1895 and then Cirsium calcareum in 1915 by Elmer Wooton and Paul Standley.  The presently accepted name of C. arizonicum was given by Franz Petrak in 1911 from a collection made by Charles Wright in southern Arizona.

"Calcareum", Latin for "spur" or "limestone", could refer to a spur on the Thistle or to calcareous soil conditions.

 

Cirsium arizonicum

Cirsium arizonicum variety bipinnatum. Synonym: Cirsium calcareum.   (Arizona Thistle)
Asteraceae (Sunflower Family)

Foothills, montane. Woodlands, openings. Spring, summer.
Navajo Reservation near Teec Nos Pos, Arizona, June 24, 2006.

Cirsium arizonicum

Cirsium arizonicum variety bipinnatum. Synonym: Cirsium calcareum.   (Arizona Thistle)
Asteraceae (Sunflower Family)

Foothills, montane. Woodlands, openings. Spring, summer.
Navajo Reservation near Teec Nos Pos, Arizona, June 24, 2006.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Range map for Cirsium arizonicum