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Cirsium (La Sal Thistle)
Cirsium (La Sal Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
La Sal Mountains, Utah, August 10, 2020.

This Cirsium grows in abundance from about 8,000' to over 10,000' in meadows and woodland edges only in the La Sal mountains of southeast Utah. The species has puzzled collectors for decades and is often treated as C. scopulorum, C. eatonii, or C. eriocephalum. When I tried to key the plant using all available resources, none of the resources led me conclusively to any species. I sought the assistance of Dave Keil (author of the Cirsium treatment in the Flora of North America), Bob Sivinski (author of the "Thistles of New Mexico"), and Jennifer Ackerfield (author of Flora of Colorado). They all agreed that this taxon was part of a high elevation group of Cirsium that varied widely in its characteristics from mountain range to mountain range. Jennifer offered one further conviction: this is an undescribed taxon which has in the past been incorrectly lumped into other species. Jennifer plans to publish this new species soon.

The La Sal Thistle commonly grow to over 3 feet tall with a very narrow upright posture and where there is one plant, there almost always are many more. Each plant has several dozen flower heads.

The summer I took these photographs was extremely dry following a near normal snowfall. With normal rainfall, this species would be more robust and would easily flower into September.

 

Cirsium (La Sal Thistle)

Cirsium (La Sal Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
La Sal Mountains, Utah, August 10, 2020.

Stems of some plants I examined were red or red striped.

Leaves are reduced in size upward on the stem.

Flower heads can be single or in groups of two, three, or four.

Cirsium (La Sal Thistle)

Cirsium (La Sal Thistle)

Cirsium (La Sal Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
La Sal Mountains, Utah, August 10, 2020.

Two key morphological details that separate this taxon from the various species it has been placed in, are the widely spreading spiny tips of the phyllaries and the dense arachnoid to tomentose pubescence.

All of the plants I saw had white florets.

Cirsium (La Sal Thistle)

Cirsium (La Sal Thistle)
Asteraceae (Sunflower Family)

Montane, subalpine. Woodlands, openings. Summer, fall.
La Sal Mountains, Utah, August 10, 2020.

Six to twelve inch long basal leaves are cut deeply, the spiny leaflets are often cut again, and the mid-rib is prominent white to green-white.