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Petrophytum caespitosum
Petrophytum caespitosum (Nutt.) Rydb.
Mat Rockspirea, Rocky Mountain Rockmat, Dwarf Spiraea, Petrophytum, Tufted Rockmat
Rosaceae (Rose Family)
Synonym(s):
USDA Symbol: PECA12
USDA Native Status: L48 (N)
Rocky Mountain Rockmat or Dwarf Spiraea’s tiny, closely packed, single-veined leaves of silver form dense cushions 1 in. high and up to 2-3 ft. across. The prostrate mat spreads from a woody rootstock to "pour" over rock surfaces. Tiny, white flowers are congested in short, bottle brush-like spikes. This plant resembles stone with thick, impenetrable, gray cushions above which white flowers bloom in dense racemes.
This strange plant is found almost exclusively in the inhospitable habitat of barren rock, clinging by stout roots jammed in crevices. There are only two other species. Chelan Rockmat (P. cinerascens), in central Washington, and Olympic Mountain Rockmat (P. hendersonii), in the Olympic Mountains of western Washington.
Plant Characteristics
Duration: PerennialHabit: Herb
Fruit Type: Aggregate , Follicle
Size Notes: Ground-hugging mat with flower spikes up to about 8 inches tall.
Fruit: Aggregated follicles.
Bloom Information
Bloom Color: WhiteBloom Time: Jun , Jul , Aug
Distribution
USA: AZ , CA , CO , ID , MT , NM , NV , OR , SD , TX , UT , WYNative Distribution: N.e. OR to CA, e. to the Black Hills & TX
Native Habitat: Granite or limestone rock crevices from foothills to alpine summits
Growing Conditions
Light Requirement: SunSoil Description: Rocks or coarse, gritty soil.
Conditions Comments: This species takes well to the rock garden.
Propagation
Description: Can be propagated from small cuttings or seed.Commercially Avail: yes
Find Seed or Plants
Find seed sources for this species at the Native Seed Network.
From the National Organizations Directory
According to the species list provided by Affiliate Organizations, this plant is on display at the following locations:Santa Barbara Botanic Garden - Santa Barbara, CA
Native Seed Network - Corvallis, OR
Web Reference
Webref 38 - Flora of North America (2019) Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.Webref 23 - Southwest Environmental Information Network (2009) SEINet - Arizona Chapter
Additional resources
USDA: Find Petrophytum caespitosum in USDA PlantsFNA: Find Petrophytum caespitosum in the Flora of North America (if available)
Google: Search Google for Petrophytum caespitosum
Metadata
Record Modified: 2023-02-22Research By: TWC Staff