General: Mat Rockspirea (Petrophyton caespitosum) is a perennial forb that grows as a dense mat over the surfaces of bare rocks. Club-like clusters of flowers are held on short stalks above the evergreen leaves. The individual flowers are typical for the Rose family, but the club-like clusters are unusual.

Mat Rockspirea is an uncommon component of vegetation communities in dry, well-drained rock (limestone) surfaces in the mountains of the Upper Sonoran (Mojave Desert Scrub and Pinyon-Juniper Woodland), Transition (Yellow Pine Forest), Canadian (Pine-Fir Forest), and Hudsonian (Bristlecone Forest) life zones.

Family: Rose (Rosaceae).

Other Names: Rock mat, rock spirea.

Plant Form: Prostrate, perennial forb. Considered a subshrub because of the woody base.

Height: leaves to an inch or so, flowering stalks to few inches.

Stems: Prostrate. Flower stalks erect.

Leaves: Evergreen, crowded together, entire, somewhat triangular.

Flowers: Blooms early summer. Inflorescence: spike. Flowers: petals white, tiny (1.5 mm); to about 40 tiny stamens. Spikes dry to a reddish-brown.

Seeds:

Habitat: Dry rock surfaces in the mountains.

Elevation: About 4,000 to 10,000 feet.

Distribution: Southwestern U.S.

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