Shrubs, evergreen or deciduous. Branchlets thorn-tipped or not. Leaves alternate; stipules deciduous, thin; blade usually herbaceous, sometimes leathery, margins entire or teeth gland-tipped, at least when young, stomata on abaxial surface not in crypts; pinnately veined or 3-veined from base. Inflorescences usually racemelike or paniclelike, sometimes umbellike. Capsules not horned, crested or not; ridges between valves absent.

Distribution

North America, Mexico, Central America (Costa Rica), Central America (Guatemala), Central America (Panama)

Discussion

Species of subg. Ceanothus not accounted for here are: Ceanothus buxifolius Willdenow ex Schultes f., C. caeruleus, C. depressus Bentham, and C. ochraceus Suessenguth; all are native to Mexico and Central America.

Species 32 (28 in the flora).

Selected References

None.

Lower Taxa

Ceanothus americanus, Ceanothus arboreus, Ceanothus cordulatus, Ceanothus cyaneus, Ceanothus dentatus, Ceanothus diversifolius, Ceanothus fendleri, Ceanothus foliosus, Ceanothus griseus, Ceanothus hearstiorum, Ceanothus herbaceus, Ceanothus impressus, Ceanothus incanus, Ceanothus integerrimus, Ceanothus lemmonii, Ceanothus leucodermis, Ceanothus martini, Ceanothus microphyllus, Ceanothus oliganthus, Ceanothus palmeri, Ceanothus papillosus, Ceanothus parryi, Ceanothus parvifolius, Ceanothus sanguineus, Ceanothus spinosus, Ceanothus thyrsiflorus, Ceanothus tomentosus, Ceanothus velutinus

Key

1	Branchlets rigid, thorn-tipped; shrubs evergreen.	> 2
2	Leaf blades pinnately veined, adaxial surfaces green, shiny, abaxial surfaces pale green.	Ceanothus spinosus
2	Leaf blades 3-veined from base (lateral basal veins sometimes obscure in C. fendleri), adaxial surfaces pale green to dark green or grayish green, dull, abaxial surfaces pale to grayish green.	> 3
3	Leaf blades 20–60 × 10–30 mm, abaxial surfaces pale green, appressed-puberulent, glabrescent, adaxial surfaces grayish green, glabrate.	Ceanothus incanus
3	Leaf blades 5–30 × 3–18 mm, abaxial surfaces pale green to grayish green, glabrous, sparsely puberulent, or appressed-villosulous to tomentulose, especially along veins, adaxial surfaces dark to pale green or grayish green, glabrous, glabrate, or appressed-villosulous.	> 4
4	Shrubs 1.5–4 m, stems erect; inflorescences usually paniclelike, sometimes racemelike, (3–)5–15 cm.	Ceanothus leucodermis
4	Shrubs 0.5–1.5 m, stems erect, ascending, or spreading; inflorescences umbel-like or racemelike, 1–3.5(–4) cm.	> 5
5	Stems ascending to spreading, not rooting at nodes; leaf blade adaxial surfaces pale to grayish green, glabrate.	Ceanothus cordulatus
5	Stems erect, ascending, or spreading, rooting at proximal nodes; leaf blade adaxial surfaces dark green, appressed villosulous or glabrous.	Ceanothus fendleri
1	Branchlets flexible to rigid, not thorn-tipped (sometimes weakly thorn-tipped in C. oliganthus); shrubs deciduous, semideciduous, or evergreen.	> 6
6	Leaf blades pinnately veined (proximal pair of secondary veins rarely more prominent and longer than distal pairs).	> 7
7	Leaf blade margins usually entire, rarely denticulate distally, adaxial surfaces glabrous or weakly puberulent.	> 8
8	Shrubs 0.3–0.8 m; inflorescences usually umbel-like, sometimes racemelike.	> 9
9	Sepals, petals, and nectaries white; petioles 0.5–1 mm.	Ceanothus microphyllus
9	Sepals, petals, and nectaries blue; petioles 1–3 mm.	Ceanothus foliosus
8	Shrubs 1–3 m; inflorescences racemelike to paniclelike.	> 10
10	Shrubs deciduous; leaf blades flat.	> 11
11	Leaf blades 6–25 mm, adaxial surfaces ± shiny; capsules usually not lobed, sometimes weakly lobed.	Ceanothus parvifolius
11	Leaf blades 20–80 mm, adaxial surfaces dull; capsules lobed.	Ceanothus integerrimus
10	Shrubs evergreen or semideciduous; leaf blades ± cupped.	> 12
12	Sepals and petals usually white, rarely pale blue; capsules lobed, valves viscid, crested; leaf blade adaxial surfaces dull to ± shiny.	Ceanothus palmeri
12	Sepals and petals pale blue to blue; capsules not lobed, valves not conspicuously viscid, not or weakly crested; leaf blade adaxial surfaces shiny.	Ceanothus spinosus
7	Leaf blade margins serrulate to denticulate (sometimes entire in C. hearstiorum), adaxial surfaces puberulent, pilosulous, villosulous, strigillose, or glandular-papillate, (sometimes glabrous in C. foliosus).	> 13
13	Leaf blade margins not revolute.	> 14
14	Shrubs 0.2–0.3(–0.5) m; stems spreading; capsules 4–5 mm wide; leaf blade surfaces pilosulous.	Ceanothus diversifolius
14	Shrubs 1–3.5 m; stems erect to ascending; capsules 3–4 mm wide; leaf blade surfaces villosulous to strigillose or glabrate.	> 15
15	Branchlets green; petiole 1–3 mm; leaf blade margins usually wavy, sometimes not.	Ceanothus foliosus
15	Branchlets pale green to grayish green and glaucous; petiole 2–8 mm; leaf blade margins not wavy.	Ceanothus lemmonii
13	Leaf blade margins revolute.	> 16
16	Branchlets lanate to woolly, glabrescent; leaf blade abaxial surfaces cobwebby, soon glabrescent; inflorescences paniclelike, 5–15 cm.	Ceanothus parryi
16	Branchlets puberulent to tomentulose; leaf blade abaxial surfaces variously hairy, but neither cobwebby nor glabrescent; inflorescences umbel- or racemelike, 1–5(–8) cm.	> 17
17	Leaf blade adaxial surfaces strigillose or sparsely puberulent, not glandular papillate.	> 18
18	Leaf blades oblong, elliptic, or suborbiculate, 6–25 × 4–15 mm, adaxial surfaces sparsely puberulent, veins furrowed.	Ceanothus impressus
18	Leaf blades narrowly elliptic, narrowly oblong, or linear, 5–16 × 2–8 mm, adaxial surfaces strigillose, veins not furrowed.	Ceanothus dentatus
17	Leaf blade adaxial surfaces glandular-papillate, sometimes also puberulent or villosulous.	> 19
19	Shrubs 1–5 m; stems erect to ascending; leaf blades 12–50 × 6–15 mm; capsules 2–3 mm wide.	Ceanothus papillosus
19	Shrubs 0.1–0.3 m; stems prostrate to spreading, some flowering branches ascending; leaf blades 8–20 × 2–10 mm; capsules 4–5 mm wide.	Ceanothus hearstiorum
6	Leaf blades 3-veined from base (proximal pair of secondary veins longer than those above, sometimes equaling central vein).	> 20
20	Leaf blade margins usually entire, rarely denticulate or serrulate distally.	> 21
21	Petioles 0.5–1 mm; leaves often fascicled, blades 2–10 × 1–6 mm; se United States.	Ceanothus microphyllus
21	Petioles (1–)1.5–12 mm; leaves not fascicled, blades 6–80 × 3–45 mm; w United States.	> 22
22	Branchlets light gray; capsules prominently rugose.	Ceanothus incanus
22	Branchlets pale green or green to grayish green or brown; capsules smooth to ± rugulose.	> 23
23	Shrubs 0.5–1 m; leaf blades widely elliptic to suborbiculate; inflorescences umbel-like to racemelike, 1.5–4 cm; sepals and petals white; nectary yellow to yellow-green.	Ceanothus martini
23	Shrubs 1–4 m; leaf blades elliptic, oblong-elliptic, lanceolate, or ovate; inflorescences racemelike to paniclelike, 3–25 cm; sepals and petals white or blue; nectary usually white or blue, rarely pink.	> 24
24	Leaf blades 6–25 mm, adaxial surfaces ± shiny; capsules usually not lobed, sometimes weakly lobed.	Ceanothus parvifolius
24	Leaf blades (10–)20–80 mm, adaxial surfaces dull; capsules lobed.	Ceanothus integerrimus
20	Leaf blade margins serrate, serrulate, or denticulate (rarely entire in C. cyaneus).	> 25
25	Leaf blades (20–)25–100(–130) × 10–64 mm, margins serrate to serrulate, teeth (35–)40–150+; sepals and petals white to cream (sometimes pink-tinged in C. sanguineus, blue in C. arboreus).	> 26
26	Leaf blades leathery, resinous, aromatic, adaxial surfaces shiny.	Ceanothus velutinus
26	Leaf blades herbaceous, not resinous, not aromatic, adaxial surfaces dull.	> 27
27	Leaf blades usually elliptic to lanceolate, sometimes ovate or oblanceolate; inflorescences terminal, globose to hemispheric.	Ceanothus herbaceus
27	Leaf blades ovate, oblong-ovate, or widely elliptic; inflorescences terminal or axillary, cylindric to conic.	> 28
28	Shrubs evergreen; branchlets brown, tomentulose; sepals, petals, and nectaries blue; California Channel Islands.	Ceanothus arboreus
28	Shrubs deciduous; branchlets green to reddish brown, puberulent, glabrescent; sepals, petals, and nectaries usually white to cream, sometimes pink-tinged; mainland United States.	> 29
29	Leaf blade apices usually acuminate to acute, rarely obtuse; capsules not lobed, valves ± rugulose, crested; e North America.	Ceanothus americanus
29	Leaf blade apices acute to rounded; capsules weakly lobed near apex, valves smooth, not or sometimes weakly crested; w North America (disjunct in Michigan).	Ceanothus sanguineus
25	Leaf blades 5–50 × 3–30 mm, margins usually denticulate, sometimes serrulate (rarely entire in C. cyaneus), teeth 19–71; sepals and petals blue (white in C. martini, rarely white in C. oliganthus and C. thyrsiflorus).	> 30
30	Leaf blade margins revolute.	> 31
31	Branchlets usually round, sometimes ± angled, in cross section, lanate to woolly, glabrescent; leaf blade abaxial surfaces cobwebby, soon glabrescent.	Ceanothus parryi
31	Branchlets angled in cross section, sparsely puberulent or glabrous; leaf blade abaxial surfaces puberulent to villosulous.	Ceanothus griseus
30	Leaf margins not revolute (sometimes incompletely revolute in C. thyrsiflorus).	> 32
32	Branchlets angled in cross section.	> 33
33	Branchlets often tuberculate (tubercles minute, brownish); inflorescences 15–30(–40) cm, paniclelike; capsules deeply lobed.	Ceanothus cyaneus
33	Branchlets not tuberculate; inflorescences 2.5–9 cm, usually racemelike, rarely paniclelike; capsules weakly lobed.	Ceanothus thyrsiflorus
32	Branchlets round in cross section (rarely angled in cross section in C. oliganthus).	> 34
34	Sepals and petals white, nectaries pale yellow to yellow-green; leaf blade margins serrulate distal to middle.	Ceanothus martini
34	Sepals and petals pale blue to blue, nectaries usually pale to dark blue or purplish blue, rarely white; leaf blade margins denticulate or serrulate most of length.	> 35
35	Branchlets reddish brown to brown; leaf blades ovate to widely elliptic.	> 36
36	Leaf blade abaxial surfaces glabrate to hirtellous; petiole 3–8 mm; capsules 4–7 mm wide.	Ceanothus oliganthus
36	Leaf blade abaxial surfaces tomentose to tomentulose; petiole 1–4 mm; capsules 3–4 mm wide.	Ceanothus tomentosus
35	Branchlets green, pale green, or grayish green; leaf blades narrowly elliptic, oblong-elliptic, or oblanceolate.	> 37
37	Branchlets green; leaf blades ± folded lengthwise, margins usually ± wavy, sometimes not; capsule valves not or weakly crested.	Ceanothus foliosus
37	Branchlets pale green to grayish green and glaucous; leaf blades flat, margins not wavy; capsule valves crested.	Ceanothus lemmonii

"thin" is not a number.