Mem. New York Bot. Gard. 1: 206. 1900.
Shrubs, 1–10+ dm diam. Stems prostrate or decumbent, loosely intertwined, 1–4+ cm, and erect or ascending, tightly coalesced, 0.2–0.5 cm, internodes 0.1–1 cm. Leaves: blade spatulate, 0.4–1.8 × 0.2–0.4 cm, venation rarely visible except on long-shoot leaves, 1 (–3) -veined, apex acute, abaxial surface pilose to sericeous, rarely sparsely strigose on lamina and veins. Panicles widely branched to compact and racemose, [0.5–] 1–15 [–20] × 0.5–6 cm, sericeous; bracts subulate to narrowly obtrullate, 3–8 mm, pilose to sericeous. Pedicels 0.5–2.5 mm; bracteoles 1, extending from middle to well beyond apex of sepals. Flowers 3–6 mm diam.; hypanthium 1 mm, densely sericeous; sepals erect, ovatelanceolate, 1–1.5 mm, margins sericeous, abaxial surface sericeous to tomentose; petals narrowly oblanceolate, 1–2.5 mm, apex obtuse to slightly cleft or acute to acuminate; stamens 20, lengths 1.5–2 (–2.5) times petals (1.5–3 times sepals); carpels (3–) 5 (–6), adaxially connate. Follicles 2 mm. 2n = 18.
Ariz., Calif., Colo., Idaho, Mont., N.Mex., Nev., S.Dak., Tex., Utah, Wash., ne Mexico
Subspecies 2 (2 in the flora).
Petrophytum caespitosum primarily inhabits arid rocky outcrops and talus slopes at high elevations in mountain ranges of the western United States and northeastern Mexico.
"dm" is not declared as a valid unit of measurement for this property.