Ceanothus thyrsiflorus |
Ceanothus arcuatus |
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blue blossom, blue blossom ceanothus |
arching ceanothus |
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Habit | Shrubs, sometimes arborescent, evergreen, 0.5–6 m. Stems erect, usually ascending to arcuate, rarely prostrate, not rooting at nodes; branchlets green, not thorn-tipped, angled in cross section, flexible, not tuberculate, sparsely puberulent or glabrous. | Shrubs, 0.3–0.8 m, moundlike. |
Stems | ascending or spreading, not rooting at nodes; branchlets brown to grayish brown, ± rigid, tomentulose, glabrescent. |
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Leaves | petiole 3–10 mm; blade flat to cupped, elliptic to ovate, 10–40(–50) × 5–15(–20) mm, base obtuse to rounded, margins denticulate to serrulate, usually not revolute, sometimes incompletely revolute, teeth glandular, 23–48, apex obtuse, abaxial surface pale green, sparsely puberulent to villosulous or glabrate, veins prominently raised, puberulent to villosulous, adaxial surface dark green, glabrate; 3-veined from base. |
sometimes fascicled, axillary short shoots ascending to spreading; petiole 1–2 mm; blade flat, elliptic to oblanceolate, 4–10 × 2–5 mm, base rounded, margins thick, not revolute, usually entire, rarely denticulate near apex, teeth 1–3, apex rounded to obtuse, abaxial surface green to pale green, glabrate, adaxial surface pale green, glabrous. |
Inflorescences | terminal, usually racemelike, rarely paniclelike, 2.5–9 cm. |
axillary or terminal, 0.8–2.5 cm. |
Flowers | sepals, petals, and nectary usually pale to deep blue, rarely white. |
sepals and petals white to pale blue; nectary pale blue or yellow tinged. |
Capsules | 3–4 mm wide, weakly lobed; valves smooth, viscid, not crested. |
4–6 mm wide, not to weakly lobed; valves smooth to rugulose, horns subapical, prominent, erect, intermediate ridges absent. |
2n | = 24. |
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Ceanothus thyrsiflorus |
Ceanothus arcuatus |
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Phenology | Flowering Mar–Jun. | Flowering May–Jun. |
Habitat | Sandy or rocky flats and slopes, maritime chaparral, open sites in mixed evergreen and conifer forests. | Granitic or serpentine soils, conifer forests. |
Elevation | 10–600 m. (0–2000 ft.) | 900–2300 m. (3000–7500 ft.) |
Distribution |
CA; OR; Mexico (Baja California)
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CA; OR |
Discussion | Ceanothus thyrsiflorus occurs along the coast from Coos County, Oregon, south to Santa Barbara County, California, and disjunctly near Eréndira, Baja California. A wide range of growth forms characterize this species and the closely related C. griseus, including plants ranging from almost prostrate to arborescent, sometimes with single trunks. Prostrate plants from several maritime bluffs along the California coast have been called C. thyrsiflorus var. repens McMinn; they retain their stature under cultivation. Named hybrids include C. ×regius (Jepson) McMinn (C. thyrsiflorus × C. papillosus) and C. ×vanrensselaeri Roof (C. thyrsiflorus × C. incanus). H. McMinn (1944) reported hybrids with C. foliosus. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Ceanothus arcuatus was explicitly described as a species by McMinn but inexplicably treated as a hybrid between C. fresnensis and C. cuneatus by P. A. Munz (1959). Munz may have been influenced by McMinn’s hypothesis that C. arcuatus was derived through hybridization between the two species. Some specimens from the Klamath Mountains have been either interpreted as C. cuneatus or misidentified as hybrids between C. pumilus and C. cuneatus. Populations of C. arcuatus are relatively uniform throughout their geographic distribution and often represent the dominant understory shrub in conifer forests of the Klamath Mountains and Sierra Nevada. Ceanothus arcuatus occurs primarily on metamorphic substrates in the Klamath Mountains and the northern Sierra Nevada, but in the central Sierra Nevada (Nevada County south to Madera County), the most common substrate is granitic. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 12, p. 90. | FNA vol. 12, p. 101. |
Parent taxa | Rhamnaceae > Ceanothus > subg. Ceanothus | Rhamnaceae > Ceanothus > subg. Cerastes |
Sibling taxa | ||
Synonyms | C. thyrsiflorus var. chandleri, C. thyrsiflorus var. repens | |
Name authority | Eschscholtz: Mém. Acad. Imp. Sci. St. Pétersbourg Hist. Acad. 10: 285. (1826) — (as thyrsiflora) | McMinn: in M. van Rensselaer and H. McMinn, Ceanothus, 247, fig. 82. (1942) |
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