Shrubs, evergreen. Branchlets not thorn-tipped. Leaves opposite (alternate in C. megacarpus and C. verrucosus); stipules persistent, thick, wartlike; blade leathery, margins entire or teeth not gland-tipped, often spinulose, stomata on abaxial surface in crypts, (crypts appearing as areolae aligned in rows between secondary-veins); pinnately veined. Inflorescences umbellike (rarely racemelike in C. pauciflorus). Capsules usually horned (horns sometimes minute or weakly developed bulges), sometimes not horned, usually not crested (crested in C. divergens and C. gloriosus); ridges between valves present or absent.

Distribution

w, sc United States, Mexico

Discussion

Species of subg. Cerastes not accounted for here are: Ceanothus australis Rose and C. bolensis S. Boyd & J. Keeley, both endemic to Mexico.

Species 25 (23 in the flora).

In the following key, references to indumentum do not include the hairs associated with the stomatal crypts, which in all species of subg. Cerastes appear microscopically tomentulose or densely puberulent; these hairs are much shorter than hairs borne on the abaxial surfaces and veins between the crypts.

Selected References

None.

Lower Taxa

Ceanothus arcuatus, Ceanothus confusus, Ceanothus crassifolius, Ceanothus cuneatus, Ceanothus divergens, Ceanothus ferrisiae, Ceanothus fresnensis, Ceanothus gloriosus, Ceanothus jepsonii, Ceanothus maritimus, Ceanothus masonii, Ceanothus megacarpus, Ceanothus ophiochilus, Ceanothus otayensis, Ceanothus pauciflorus, Ceanothus perplexans, Ceanothus pinetorum, Ceanothus prostratus, Ceanothus pumilus, Ceanothus purpureus, Ceanothus roderickii, Ceanothus sonomensis, Ceanothus verrucosus

Key

1	Leaves alternate.	> 2
2	Leaf blades widely obovate to suborbiculate, 5–14 mm, apices truncate to retuse; capsules 4–6 mm wide, valves smooth, horns minute or absent.	Ceanothus verrucosus
2	Leaf blades elliptic to obovate, 10–25(–33) mm, apices obtuse; capsules 7–12 mm wide, valves rugulose to weakly ridged near apex, horns prominent.	Ceanothus megacarpus
1	Leaves opposite.	> 3
3	Shrubs matlike to moundlike, 0.1–1 m; stems spreading to weakly ascending (sometimes erect to ascending in C. maritimus and C. sonomensis), sometimes rooting at nodes.	> 4
4	Shrubs matlike, 0.1–0.3 m; stems prostrate or spreading.	> 5
5	Leaf blade margins sharply dentate to spinose-dentate, teeth 3–9.	> 6
6	Leaves not crowded (shorter than internodes); leaf blade adaxial surfaces green, dull; capsules 4–6 mm wide.	Ceanothus confusus
6	Leaves often crowded (usually longer than internodes); leaf blade adaxial surfaces dark green, shiny; capsules 6–9 mm wide.	Ceanothus prostratus
5	Leaf blade margins entire or denticulate near apex, teeth 0–3.	> 7
7	Leaf blade adaxial surfaces dark green, shiny, apices rounded to retuse; capsule horns prominent.	Ceanothus fresnensis
7	Leaf blade adaxial surfaces green to grayish green, dull, apices usually truncate, sometimes obtuse; capsule horns minute or weakly developed bulges.	Ceanothus pumilus
4	Shrubs moundlike, 0.1–1 m; stems ± prostrate, spreading, or weakly ascending.	> 8
8	Leaf blade margins spinose-dentate.	> 9
9	Leaf blades widely obovate to suborbiculate, 5–12 mm, apices widely notched, marginal teeth 2–4.	Ceanothus sonomensis
9	Leaf blades elliptic, ± oblong, or obovate, 10–20 mm, apices acute or retuse, with an apical tooth, marginal teeth 3–9(–11).	> 10
10	Shrubs 0.5–1.5 m; stems ascending to erect.	Ceanothus divergens
10	Shrubs 0.1–0.6 m; stems spreading to weakly ascending.	Ceanothus confusus
8	Leaf blade margins entire, denticulate, or serrulate.	> 11
11	Leaf blade abaxial surfaces tomentulose.	Ceanothus maritimus
11	Leaf blade abaxial surfaces strigillose, sometimes only on or between veins, puberulent, or glabrate.	> 12
12	Leaf blade margins dentate to denticulate or serrulate most of length, teeth 5–31.	> 13
13	Leaves crowded, blades elliptic to obovate, marginal teeth 5–9.	Ceanothus prostratus
13	Leaves not crowded, blades widely elliptic, obovate, or suborbiculate, marginal teeth 9–31.	> 14
14	Leaf blades 23–31(–45) mm, marginal teeth 13–31; capsule horns minute, intermediate ridges absent; coastal habitats, 30–200 m.	Ceanothus gloriosus
14	Leaf blades 10–20 mm, marginal teeth 9–15; capsule horns prominent, intermediate ridges present; montane habitats, elevations 1600–2600 m.	Ceanothus pinetorum
12	Leaf blade margins entire, denticulate near apex, or remotely denticulate, teeth 1–5(–7).	> 15
15	Leaf blades narrowly oblanceolate to narrowly oblong-lanceolate, margins thick to ± revolute, apex usually truncate, sometimes obtuse.	Ceanothus pumilus
15	Leaf blades elliptic to oblanceolate, margins sometimes thick but not revolute, apex acute, obtuse, retuse, or rounded, or ± truncate.	> 16
16	Leaf blades folded lengthwise; capsule horns absent or weakly developed bulges; axillary short shoots, if present, erect.	Ceanothus roderickii
16	Leaf blades flat; capsule horns prominent to minute or absent; axillary short shoots, if present, ascending to spreading.	> 17
17	Leaf blades apices rounded to obtuse, adaxial surfaces pale green; capsule horns subapical, erect.	Ceanothus arcuatus
17	Leaf blades apices acute to ± truncate; adaxial surfaces grayish green; capsule horns minute or absent, or lateral, spreading.	Ceanothus pauciflorus
3	Plants not matlike or moundlike, 0.5–6 m; stems usually erect to ascending, sometimes spreading, not rooting at nodes.	> 18
18	Leaf blade margins spinose-dentate.	> 19
19	Stems ± flexible; leaves spreading, abaxial leaf surfaces grayish green.	Ceanothus divergens
19	Stems rigid; leaves spreading to deflexed, abaxial leaf surfaces pale green or pale yellowish green.	> 20
20	Sepals, petals, and stamens 5; leaf blade adaxial surfaces green to dark green; capsule valves smooth, horns slender, intermediate ridges absent; on volcanic soils.	Ceanothus purpureus
20	Sepals, petals, and stamens (5–)6(–8); leaf blade adaxial surfaces pale green; capsule valves rugose, horns thick, intermediate ridges present; on serpentine soils.	Ceanothus jepsonii
18	Leaf blade margins entire, dentate, denticulate, or serrulate.	> 21
21	Leaf blade margins entire or remotely denticulate, teeth if present minute, 1–7 (8–19 in C. crassifolius).	> 22
22	Leaves both fascicled and not fascicled on same plant.	> 23
23	Petioles 1–3 mm; leaf blades elliptic, oblanceolate, obovate, or orbiculate, 6–22(–30) × 3–12(–22) mm; capsules 4–6 mm wide, horns prominent.	Ceanothus cuneatus
23	Petioles 0–1 mm; leaf blades narrowly oblanceolate to narrowly obovate, 3–7 × 1–3 mm; capsules 3–4 mm wide, horns minute or absent.	Ceanothus ophiochilus
22	Leaves not fascicled.	> 24
24	Branchlets light gray to ashy gray, puberulent to tomentulose, hairs curly or wavy, glabrescent; leaf blade adaxial surfaces grayish green, puberulent, hairs curly or wavy, glabrescent.	Ceanothus pauciflorus
24	Branchlets grayish brown to brown, puberulent or tomentulose, hairs straight, sometimes glabrate; leaf blade adaxial surfaces green, glabrous or sparsely tomentulose, hairs straight, glabrescent.	> 25
25	Leaf blades widely oblanceolate to widely obovate, 5–11 × 4–7 mm; sepals, petals, and nectaries usually lavender, sometimes pale blue; capsules 5–6 mm wide.	Ceanothus cuneatus
25	Leaf blades elliptic to obovate, 10–40 × 5–15(–20) mm; sepals and petals white, nectaries blue or black; capsules 6–12 mm wide.	> 26
26	Leaf blade abaxial surfaces glabrous or strigillose on veins; capsules 7–12 mm wide, horns weakly developed or absent.	Ceanothus megacarpus
26	Leaf blade abaxial surfaces tomentulose; capsules 6–9 mm wide, horns prominent.	Ceanothus crassifolius
21	Leaf blade margins dentate or denticulate, at least distal to middle, teeth 5–35 (3–5 in C. otayensis).	> 27
27	Sepals and petals white to cream, nectaries tan to brown, yellow to green, blue, purple, or black.	> 28
28	Leaf blade margins revolute or thick, abaxial surfaces tomentulose.	> 29
29	Leaf blade margins with 8–19 teeth most of length, apices obtuse to rounded; capsules 5–9 mm wide, horns prominent.	Ceanothus crassifolius
29	Leaf blades margins with 3–5 teeth near apex, apices truncate, retuse, or cuspidate; capsules 4–6 mm wide, horns minute or absent.	Ceanothus otayensis
28	Leaf blade margins thick or not, not revolute, abaxial surfaces sparsely puberulent (hairs curly) or strigillose, sometimes glabrescent.	> 30
30	Leaf blade adaxial surfaces dark green; nectaries dark blue to purple; capsules 7–9 mm wide, horns subapical, prominent; serpentine substrates.	Ceanothus ferrisiae
30	Leaf blade adaxial surfaces green to yellowish green; nectaries yellow to green; capsules 4–6 mm wide, horns lateral, usually minute, sometimes absent; granitic or metamorphic substrates.	Ceanothus perplexans
27	Sepals, petals, and nectaries pale blue, blue, or purple.	> 31
31	Leaf blades 4–10 × 4–6 mm, margins denticulate distal to middle, teeth 5–9.	Ceanothus cuneatus
31	Leaf blades 7–40 × 4–22 mm, denticulate most of length, teeth 9–35.	> 32
32	Sepals, petals, and nectaries pale blue to blue; capsule horns prominent, rugose, intermediate ridges present; montane habitats, 1600–2600 m.	Ceanothus pinetorum
32	Sepals, petals, and nectaries deep blue to purple; capsule horns minute, not rugose, intermediate ridges absent; coastal habitats, 30–500 m.	> 33
33	Leaf blades widely elliptic to suborbiculate, 3–40 × 17–22 mm, marginal teeth 13–35.	Ceanothus gloriosus
33	Leaf blades usually elliptic or oval, sometimes suborbiculate, 7–21 × 4–13 mm, marginal teeth 9–17.	Ceanothus masonii

"thick" is not a number.