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Montana Field Guide

Montana Field Guides

Caespitose Rockmat - Petrophytum caespitosum
Other Names:  Petrophyton caespitosum

Native Species

Global Rank: G5
State Rank: S5
(see State Rank Reason below)

Agency Status


External Links

State Rank Reason (see State Rank above)
Very common on calcareous rocks in Montana and elsewhere. A widely ranging species in the interior west. Rare in some outlying stations, but common in its core range.
General Description
Mat-forming shrub. Stems branched, prostrate, clothed in old leaf bases; erect stems scapose, 3–10 cm. Leaves basal and cauline, exstipulate, short-petiolate, oblanceolate, glabrate to sericeous, entire, 3–12 mm long; cauline reduced, bract-like. Inflorescence a dense, cylindrical raceme, 1–4 cm long. Flowers perfect, 5-merous, perigynous; hypanthium cup-shaped, sericeous; sepals 1–2 mm long, deltoid; petals white, 1.5–2.5 mm long; stamens 20 to 40; styles usually 5. Fruit a 1- to 2-seeded follicle, ca. 3 mm long (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Species Range

Range Comments
OR to SD, south to CA, AZ, NM, TX and Mexico (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 75

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Crevices of cliffs and rock outcrops, usually on limestone; montane to alpine (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

  • Literature Cited AboveLegend:   View Online Publication
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Culver, D.R. 1994. Floristic analysis of the Centennial Region, Montana. M.Sc. Thesis. Montana State University, Bozeman. 199 pp.
    • Quire, R.L. 2013. The sagebrush steppe of Montana and southeastern Idaho shows evidence of high native plant diversity, stability, and resistance to the detrimental effects of nonnative plant species. M.Sc. Thesis. Bozeman, MT: Montana State University. 124 p.
  • Web Search Engines for Articles on "Caespitose Rockmat"
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Citation for data on this website:
Caespitose Rockmat — Petrophytum caespitosum.  Montana Field Guide.  .  Retrieved on , from