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Tetradymia canescens
Tetradymia canescens (Gray Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Openings, shrublands. Summer.
Carpenter Natural Area, Cortez, June 24, 2013.

These Tetradymia canescens shrubs are 2 1/2 feet tall and 9 feet long overall. The back shrub appears a bit yellow because its flowers are just starting to emerge.

Tetradymia canescens
Tetradymia canescens (Gray Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Openings, shrublands. Summer.
Carpenter Natural Area, Cortez, August 20, 2016.

Even in seed, Tetradymia canescens attracts attention. This Tetradymia canescens is about three feet tall and five wide.

Tetradymia canescens

Tetradymia canescens

Tetradymia canescens (Gray Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Openings, shrublands. Summer.
Near McPhee Reservoir, July 21, 2005 and
Carpenter Trail, Cortez, August 17, 2016.

Tetradymia canescens grows to three or four feet wide and tall. It inhabits dry foothill meadows and roadsides and stands out especially because of its very gray (Latin, "canescens") leaves, its massing of golden flowers, and its silvery plumes that carry the seeds. In flower, Tetradymia canescens is easily mistaken for a Rabbitbrush; it is a close cousin.

"Tetradymos" means "four-sided", referring to the four phyllaries that subtend the flower head (see photographs below). "Canescent" is Latin for "becoming gray", i.e., there is such an abundance of matted, short gray or white hairs that the surface appears gray or white.

The first plant of this species was collected for science by David Douglas near the Columbia River in the early 1830s. This was the first member of its genus. Augustin de Candolle named both the genus and this species in 1838.

Tetradymia canescens
Tetradymia canescens (Gray Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Openings, shrublands. Summer.
Near McPhee Reservoir, July 21, 2005.

Tetradymia canescens presents a very soft and velvety appearance, quite in contrast to its ragged, thorny cousin, Tetradymia spinosa, pictured below.

Tetradymia canescens

Tetradymia canescens

Tetradymia canescens (Gray Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills, montane. Openings, shrublands. Summer.
Carpenter Natural Area, Cortez, June 24, 2013 and Near McPhee Reservoir, July 21, 2005.

Pappus hairs emerge beyond the phyllaries before the flowers. Notice the prominent mid-vein on the leaves.

There are four flowers in each flower head.

 

Tetradymia spinosa

Tetradymia spinosa

Tetradymia spinosa

Tetradymia spinosa (Cat-claw Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills. Openings, shrublands. Spring.
Above: Lower Cross Canyon, Utah, May 2, 2016.
Left: Canyons of the Ancients National Monument, April 27, 2007.

Although this species of Tetradymia shares a number of characteristics with T. canescens, it is distinguished in two major ways:  it has very prominent hooked spines (see below) and it blooms in the spring, not summer.  T. spinosa is densely white hairy with a multitude of bright flowers; these characteristics might lure you to touching the plant, but the spines quickly put an end to this intimacy.

William Hooker and George Arnott named this species in 1839 from a specimen collected by Tolmie in Idaho.

Tetradymia spinosa

Tetradymia spinosa (Cat-claw Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills. Openings, shrublands. Spring.
Lower Cross Canyon, Utah, May 12, 2013.

The branches are young in this photograph and the new spines are pliable and not threatening. When the spines become woody, they are curved, sharp, and blood-thirsty.

Tetradymia spinosa
Tetradymia spinosa (Cat-claw Horsebrush)
Asteraceae (Sunflower Family)

Semi-desert, foothills. Openings, shrublands. Spring.
Canyons of the Ancients National Monument, April 27, 2007.

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 Tetradymia canescens

Range map for Tetradymia spinosa