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

Montane to alpine.  Openings, scree. Summer.  July 17, 2010.

This very prickly native Thistle grows 20-60 inches tall at maturity.  The plant usually has a very erect posture with narrow, hairless, shiny leaves and tight clusters of very attractive lavender flowers. 

The Flora of North America observes, "Variety hesperium is distributed [only] in the San Juan Mountains and Spanish Peaks area of southern Colorado."

The genus was named by Philip Miller (1691-1771).  Asa Gray gave this species its first scientific name but I have been unable to determine that name.  In any case, the name Gray gave was changed by B. L. Robinson to Cirsium eatonii.  Alice Eastwood named this plant Cnicus hesperius in 1898 and Petrak renamed it Cirsium hesperium.  In 2004 D. J. Keil indicated that C. hesperium is a variety of C. eaton. 

Daniel Eaton, Yale Botany Professor, fern specialist, and plant collector, was the first collector of this plant.  (More biographical information about Eaton.)

Cirsium eatonii variety hesperium (Thistle)
Asteraceae (Sunflower Family) 

Montane to alpine.  Openings, scree. Summer.  July 17, 2010.

Cirsium eatonii variety hesperium (Thistle)
Asteraceae (Sunflower Family) 

Montane to alpine.  Openings, scree. Summer.  July 17, 2010.

Cirsium eatonii variety hesperium (Thistle)
Asteraceae (Sunflower Family) 

Montane to alpine.  Openings, scree. Summer.  July 17, 2010.

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 all varieties Cirsium eatonii