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   Thomas Nuttall was the first to collect this plant for science; he found it on his 1834-1837 trip to the Pacific, "on high shelving rocks in the Rocky Mountains, towards the sources of the Platte". (Nuttall's words as quoted in Intermountain Flora.)  Nuttall named the plant Spiraea caespitosa in 1840; Per Axel Rydberg realized that the plant is not a Spiraea and he renamed it Petrophyton caespitosum in 1900.

   "Petro" "phyton" is Latin for "rock" "plant" and "caespitosum" means "growing in clumps".

Petrophyton caespitosum (Rockmat)
Rosaceae (Rose Family)

Canyons. Summer, fall.
Location not disclosed to protect the plants, April 1, 2004 and September 10, 2005.

In the photograph at left, last year's dried flowers are golden brown; this year's flower stalks have not yet begun to emerge.  When they do they will grow to about four inches long topped by a star burst of white.  

Rockmat roots penetrate moist cracks in shallow overhangs and deeper alcoves; the plant clings precariously.  Petrophyton caespitosum often forms balls of vegetation around its own or other plants' roots.  This is a very lovely and exotic plant that is always a thrill to find.

Petrophyton caespitosum
Petrophyton caespitosum (Rockmat)
Rosaceae (Rose Family)

Canyons. Summer, fall.
Location not disclosed to protect the plants, April 14, 2004.

The top of this two foot long plant is attached to the rock wall; the rest of the plant swings gently in a breeze. 

Petrophyton caespitosum (Rockmat)
Rosaceae (Rose Family)

Canyons. Summer, fall.
Location not disclosed to protect the plants, September 10, 2005.

Petrophyton caespitosum (Rockmat)
Rosaceae (Rose Family)

Canyons. Summer, fall.
Location not disclosed to protect the plants, April 1, 2004.

Where there's a seep of water, life clings.  Each of those dark spots running from left to right through the center of the photograph is a Petrophyton caespitosum about a foot in diameter.

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 Petrophyton caespitosum