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Cirsium clavatum var. americanum
Cirsium clavatum  var. americanum (Fish Lake Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
Lower Calico National Recreation Trail, August 12, 2019.

Almost all of the morphological characteristics that you see in the photographs and that you read below are highly variable The Flora of North America ends its description of C. clavatum, "Cirsium clavatum is a polymorphic and variable species". Here, for instance is the FNA description of the leaves:

blades oblong to oblanceolate or elliptic, 5–40 × 3–11 cm, unlobed and merely spinulose-dentate or more commonly regularly deeply pinnatifid, lobes well separated to crowded, linear to triangular-ovate, ascending-spreading to retrorse, merely spinulose to coarsely dentate or proximally few-lobed, main spines 2–5(–7) mm, slender, abaxial faces green to gray, glabrous or thinly to densely arachnoid-tomentose, sometimes glabrate, often villous with septate trichomes along veins, adaxial green, glabrous; basal usually present at flowering, sessile or petiolate; principal cauline well distributed, proximal usually winged-petiolate, mid sessile, decurrent as spiny wings 1–3 cm; distal cauline ± reduced. 

Mature plants range from 8 inches tall to three feet tall, two+ feet as shown at right. Almost every morphological detail of the plant can vary just as widely as the leaf shape or height, having two or three or four other forms or dimensions. The FNA gives us a good spread of the variations, but some floras make the species sound much more predictable. It is not. David Keil, author of the FNA Cirsium summarizes his description of C. clavatum var. americanum thusly:

Variations in leaf characteristics, head size, and phyllary features combined with a narrow species concept led Osterhout and Rydberg to propose several species and hybrids for what I am treating as one taxon. Variety americanum certainly is polymorphic and in need of further study focused on local and regional variation. It is possible that some of the local variants in Colorado may deserve taxonomic recognition, but I have been unable to detect consistent patterns in the variation.

As the maps below indicate, variety americanum is the most widely distributed of the C. clavatum varieties.

Marcus Jones was the first to collect Cirsium clavatum for science in 1894 at Fish Lake , Sevier County, Utah. Jones named the species, Cnicus clavatus and that name remained until Petrak changed it to Cirsium clavatum in 1917. Variety americanum was first named Cnicus carlinoides var. americanus in 1874 by Asa Gray from a collection made in "Rocky Mountains of Colorado Territory" by Hall and Harbour under the guidance of Charles Parry in 1871. The name was changed to Cirsium clavatum var. americanum by D. J. Keil in 2004.

Cirsium clavatum var. americanum

Cirsium clavatum var. americanum

Cirsium clavatum  var. americanum (Fish Lake Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
Lower Calico National Recreation Trail, August 12, 2019.

Involucres are often nearly spherical with spreading spines, some dagger-like in variety americanum. Peduncles can be anywhere from 0 to 30 cm long.                                                                                                  Cirsium clavatum var. americanum

 

Cirsium clavatum var. americanum

Cirsium clavatum var. americanum

Cirsium clavatum var. americanum

Cirsium clavatum  var. americanum (Fish Lake Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
Lower Calico National Recreation Trail, August 12, 2019.

Six to ten inch basal leaves are a common site along forest trails in the western San Juans. Cauline leaves can be as long but are often reduced in size upward. The upper side of leaves is glabrous; the lower side may be glabrous or hairy. As the second and third photographs at left show, the spines are widely spaced, mid-veins are prominent, and the base of the leaves may have a wing-like appendage partially wrapping around the stem.

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

Cirsium clavatum var. americanum

Range map for Cirsium clavatum var. americanum

Cirsium clavatum var. clavatum

Range map for Cirsium clavatum var. clavatum

Cirsium clavatum var. osterhoutii

Range map for Cirsium clavatum var. osterhoutii