Petrophytum caespitosum |
Petrophytum caespitosum subsp. acuminatum |
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mat rock-spirea, rockmat spirea, rockrose, Rocky Mountain rockmat |
marble rockmat |
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Habit | 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. |
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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. |
blades 1–1.8 cm, abaxial surface sparsely strigose. |
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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. |
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Inflorescences | compressed panicles, usually appearing racemose, with scattered bracts along peduncle, branches uncommon, 0.5–1 cm. |
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Pedicels | 0.5–2.5 mm; bracteoles 1, extending from middle to well beyond apex of sepals. |
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Flowers | 3–6 mm diam.; hypanthium 1 mm, densely sericeous; sepals erect, ovate-lanceolate, 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. |
petal apex acute to acuminate. |
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Follicles | 2 mm. |
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Short | shoots compressed into tight rosettes. |
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2n | = 18. |
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Petrophytum caespitosum |
Petrophytum caespitosum subsp. acuminatum |
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Phenology | Flowering Jun–Sep. | |||||
Habitat | Limestone cliffs | |||||
Elevation | 1200–2500 m (3900–8200 ft) | |||||
Distribution |
AZ; CA; CO; ID; MT; NM; NV; SD; TX; UT; WA; ne Mexico
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CA |
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Discussion | 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. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Of conservation concern. Subspecies acuminatum is known only from the southern Sierra Nevada in Fresno and Tulare counties. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 9, p. 413. | FNA vol. 9, p. 414. | ||||
Parent taxa | Rosaceae > subfam. Amygdaloideae > tribe Spiraeeae > Petrophytum | Rosaceae > subfam. Amygdaloideae > tribe Spiraeeae > Petrophytum > Petrophytum caespitosum | ||||
Sibling taxa | ||||||
Subordinate taxa | ||||||
Synonyms | Spiraea caespitosa, Eriogynia caespitosa, Luetkea caespitosa | P. acuminatum | ||||
Name authority | (Nuttall) Rydberg: Mem. New York Bot. Gard. 1: 206. (1900) | (Rydberg) Munz: Aliso 4: 92. (1958) | ||||
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