Petrophytum cinerascens
Rosaceae tribe Spiraeeae
Chelan rockmat, halfshrub rockmat
prostrate to decumbent, 2–8 cm, internodes (0.1–)1(–2) cm.
blade oblanceolate to obtuse, 1–2.5(–3) × 0.2–0.4(–0.5) cm, palmately 3-veined, venation sometimes visible through hairs, apex obtuse, abaxial surface minutely canescent to strigose or cinereous, adaxial sometimes glandular.
alternate, simple or pinnately compound;
stipules absent;
venation pinnate, sometimes palmate.
sometimes branched, 2–8(–15) × 1–5 cm, canescent to puberulent;
bracts linear to oblanceolate, 5–10 mm, pilose.
0.5–2(–4) mm;
bracteoles 1(–2), extending from middle to apex of sepals, rarely beyond.
2–4(–6) mm diam.;
hypanthium 1 mm, canescent;
sepals erect, ovate or lanceolate, 1–1.5 mm, margins ciliate, abaxial surface pubescent, glandular;
petals oblanceolate or narrowly ovate, 1–2.5 mm, apex acute or rounded;
stamens 20–25, lengths 1.3 times petals (1.3–1.5 times sepals);
carpels (3–)5(–6), distinct.
perianth and androecium perigynous;
epicalyx bractlets absent or present;
hypanthium shallowly bowl-shaped, hemispheric, campanulate, patelliform, +/- crateriform, or turbinate;
torus absent, minute, or thickened;
carpels 3–5(or 6)[–8], distinct, free or adnate to hypanthium base, styles +/- terminal, distinct;
ovules 2–5, apical, collateral or clustered.
aggregated follicles or achenes (Holodiscus);
styles deciduous or persistent, not elongate.
2 mm.
Petrophytum cinerascens
Rosaceae tribe Spiraeeae
Of conservation concern.
Petrophytum cinerascens grows in crevices and ledges of outcrops above the Columbia River where there is little or no soil; it was found only on rocky outcrops of gneiss, schist, and granite between Chelan and Wenatchee in central Washington (D. J. Moore et al. 1998); C. L. Hitchcock et al. (1955–1969, vol. 3) erroneously cited its habitat as basaltic cliffs, which is the more common rock type on the Columbia River plateau. Moore et al. evaluated the ability of P. cinerascens for photosynthetic acclimation to increased growth temperature and drought stress under short-term experimental conditions, and concluded that it could not acclimate to such changes; they suggested that this endemic species might be at risk of extinction if warmer, drier local conditions result from projected climate changes.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Genera 8, species ca. 130 (6 genera, 25 species, including 3 hybrids, in the flora).
The two genera not present in North America north of Mexico are the southeastern European-western Asian Sibiraea Maximowicz (five species) and the Mexican Xerospiraea J. Henrickson (one species).
The base chromosome number for Spiraeeae is x = 9.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Herbs, perennial; flowers unisexual; hypanthia shallowly bowl-shaped. | Aruncus |
1. Shrubs or subshrubs; flowers bisexual; hypanthia hemispheric, campanulate, patelliform, +/- crateriform, or turbinate | → 2 |
2. Subshrubs; leaves 2–3(–5)-ternate, primarily crowded basally. | Luetkea |
2. Shrubs; leaves simple, cauline (tightly clustered in Petrophytum) | → 3 |
3. Leaves deciduous, herbaceous, membranous, chartaceous, rarely coriaceous; stems erect, arching, or ascending, sometimes spreading to prostrate in Spiraea | → 4 |
3. Leaves persistent, often marcescent, coriaceous; stems prostrate (mat-forming), sometimes ascending or erect in Petrophytum | → 5 |
4. Fruits aggregated follicles; inflorescences panicles or corymbiform or racemiform; carpels free; petals greenish, yellowish, white, pink, or purple. | Spiraea |
4. Fruits aggregated achenes; inflorescences panicles; carpels adnate to hypanthium base; petals usually white, sometimes pink tinged, rarely pink. | Holodiscus |
5. Inflorescences panicles; petals white; stamens 20–40. | Petrophytum |
5. Inflorescences: flowers solitary; petals pink to pinkish, often purple tinged; stamens 7–12. | Kelseya |
WA
Flora NW
PNW Herbaria
WildflowerSearch
iNaturalist
USDA Plants Database
