Flower profile

Mat rock spiraea

Petrophytum caespitosum

Mat rock spiraea (Petrophytum caespitosum) is a low shrub in the Rosaceae family, native in the lower 48 states, blooming mostly August–October across the U.S.

Native in the lower 48

Mat rock spiraea is a flowering plant that USDA PLANTS lists as native in the lower 48 states. It's on our flower lists for 2 states, and across the U.S. it's most often seen in bloom in August–October.

12states where USDA records it

2Bloomipedia state lists include it

3,990U.S. sightings*

*iNaturalist research-grade observations, as of October 17, 2026.

On our lists for: Nevada, Utah

Quick look

Petrophytum caespitosum is a woody perennial species of flowering plant in the rose family known by the common name mat rock spiraea and native to western United States.
From Wikipedia's article Petrophytum caespitosum, CC BY-SA 4.0.

It belongs to the Rosaceae family. ^iNaturalist
USDA PLANTS describes it as a subshrub with a perennial life cycle. ^{USDA PLANTS}
USDA PLANTS lists it as native in the lower 48 states and records it in 12 states. ^{USDA PLANTS}
NatureServe lists it as native to Utah and Nevada. ^NatureServe
In Nevada, most iNaturalist sightings of it in flower come in July–September. ^iNaturalist
iNaturalist has 1,428 research-grade sightings of it in Utah, ranking #29 among the 153 flowers on our Utah list. ^iNaturalist
iNaturalist has 788 research-grade sightings of it in Nevada, ranking #45 among the 132 flowers on our Nevada list. ^iNaturalist

When does it bloom?

Flowering records by month across the U.S. (iNaturalist research-grade observations marked “Flowering”) (180 records)

Bloom time in the 2 states whose Bloomipedia list includes it

State	Type	Peak bloom	Sightings*
Utah	Native	few records (28)	1,428
Nevada	Native	July–September	788

Conservation status

Federal (U.S. ESA): Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. ^{USFWS ECOS}
NatureServe global: G5 Secure worldwide. ^NatureServe
Utah: No list Utah has no state law listing endangered or threatened plants, so we show NatureServe's Utah ranks instead. NatureServe: SNR, not yet ranked in Utah.
Nevada: Not listed Not on Nevada fully protected plants, critically endangered (NAC 527.010). NatureServe: S4, apparently secure in Nevada. ^{NAC 527.010}
Rare elsewhere: No other U.S. state ranks it S1, S2, SH or SX.

Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.

Can you eat it?

For peopleNot well documented

None of the sources we checked (NC State Extension (no page for this plant), USDA PLANTS) say whether it's edible or poisonous for people.

For petsNot well documented

It isn't on the ASPCA plant list.

🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.

Where does it grow?

USDA PLANTS records mat rock spiraea in 12 states.

AKMEVTNHWAIDMTNDMNILWIMINYRIMAORNVWYSDIAINOHPANJCTCAUTCONEMOKYWVVAMDDEAZNMKSARTNNCSCDCOKLAMSALGAHITXFL

recorded by USDA PLANTS on our state lists not recorded

See the full list of states

Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, South Dakota, Texas, Utah, Wyoming.

Utah counties with USDA records: Beaver, Box Elder, Cache, Daggett, Duchesne, Garfield, Grand, Iron, Juab, Kane, Millard, Piute, Salt Lake, San Juan, Summit, Tooele, Uintah, Utah, Washington, Wayne.

Nevada counties with USDA records: Elko, Lander, Lincoln, White Pine.

Names, range and relatives

County records: USDA PLANTS lists it in 75 counties across 11 states; the most are in Utah (20), Idaho (15), Wyoming (9).

More from the Rosaceae family (103 on Bloomipedia; most observed first): Roses (genus Rosa), Multiflora rose, Mock strawberry, Black cherry, Toyon, Thimbleberry, Wineberry, Black raspberry.

More Utah flowers

Stansbury's cliffrose

Purshia stansburyana

Native

🌼 Blooms in UT: April–June

Curlleaf Mountain mahogany

Cercocarpus ledifolius

Native

🌼 Few flowering records in UT

Utah serviceberry

Amelanchier utahensis

Native

🌼 Blooms in UT: March–May

Sources

USDA, NRCS. PLANTS Database, profile PECA12.
iNaturalist, Petrophytum caespitosum: taxonomy, research-grade observation counts and “Flowering” annotations, retrieved October 17, 2026.
Wikipedia, Petrophytum caespitosum (lead quoted under CC BY-SA 4.0).
Utah: Utah noxious weed list (Utah Admin. Code R68-9-3).
Nevada: Nevada fully protected plants, critically endangered (NAC 527.010).
Nevada: Nevada noxious weeds (NAC 555.010).
USFWS, ECOS species database (ESA listing check), October 17, 2026.
NatureServe Explorer, Petrophytum caespitosum (global and state ranks).
Edibility and toxicity: no source found (marked "not well documented").
Photo: Evan M. Raskin via iNaturalist · CC BY 4.0 · resized.