Erythea 1: 149. 1893.
Shrubs, 0.1–0.4 m, matlike to moundlike. Stems prostrate to spreading, sometimes rooting at proximal nodes; branchlets reddish-brown, flexible to ± rigid, tomentulose. Leaves not fascicled; petiole 1–2 mm; blade flat to ± cupped, slightly folded lengthwise adaxially, narrowly oblanceolate to narrowly oblong-oblanceolate, 5–15 × 3–6 mm, base cuneate, margins thick to ± revolute, usually denticulate near apex, sometimes entire, teeth (0 or) 2–3, apex usually truncate, sometimes obtuse, abaxial surface pale green, sparsely strigillose to glabrous, adaxial surface green to grayish green, dull, glabrous, sometimes glaucous. Inflorescences axillary, 1–1.7 cm. Flowers: sepals, petals, and nectary pale blue to lavender. Capsules 4–6 mm wide, lobed; valves smooth, horns subapical, minute or weakly developed bulges, intermediate ridges absent. 2n = 24.
Phenology: Flowering Apr–Jun.
Habitat: Rocky soils derived from serpentine, open flats and slopes, chaparral, conifer forests.
Elevation: 100–2200 m.
Ceanothus pumilus is endemic to the Klamath Mountains, where it occurs strictly on serpentine soils; it sometimes has been confused with C. arcuatus and C. prostratus, from which it differs principally by its oblanceolate to oblong-lanceolate leaf blades with a truncate, 3-toothed apex.
Hybrids between Ceanothus pumilus and C. cuneatus have been called C. ×humboldtensis Roof.
"thick" is not a number.