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FNA | Family List | FNA Vol. 12 | Rhamnaceae

12. Ceanothus incanus Torrey & A. Gray, Fl. N. Amer. 1: 265. 1838.

Coast whitethorn Coast whitethorn

Shrubs, evergreen, 1–4 m. Stems erect, not rooting at nodes; branchlets light gray, glaucous, thorn-tipped or not, round or slightly angled in cross section, rigid, puberulent, glabrescent. Leaves not fascicled; petiole 3–12 mm; blade flat, elliptic, ovate, or suborbiculate, 20–60 × 10–30 mm, base rounded or subcordate, margins entire, sometimes minutely glandular-denticulate above middle, glands 26–52, apex obtuse, abaxial surface pale green, appressed-puberulent, glabrescent, adaxial surface grayish green, dull, glabrate; 3-veined from base. Inflorescences axillary, usually paniclelike, sometimes racemelike, 3–6 cm. Flowers: sepals, petals, and nectary usually white to cream, sometimes pink. Capsules 4–5 mm wide, ± lobed; valves rugose, viscid when young, not or weakly crested. 2n = 24.

Flowering Apr–Jun. Flats, slopes, chaparral, open sites in conifer and mixed evergreen forests; 60–1000 m; Calif.

Ceanothus incanus is restricted to the Klamath and Santa Cruz mountains and North Coast Ranges of California. Some populations are evidently polymorphic for the presence of thorn-tipped or non-thorn-tipped branchlets (F. K. Klein 1970). Putative hybrids with C. papillosus and C. parryi have been reported (H. McMinn 1944); hybrids with C. thyrsiflorus have been called C. ×vanrensselaeri Roof.


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