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FNA | Family List | FNA Vol. 12 | Rhamnaceae

13a. Ceanothus Linnaeus subg. Ceanothus

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 umbel-like. Capsules not horned, crested or not; ridges between valves absent.

Species 32 (28 in the flora): North America, Mexico, Central America (Costa Rica, Guatemala, Panama).

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.

1 Branchlets rigid, thorn-tipped; shrubs evergreen   (2)
+ Branchlets flexible to rigid, not thorn-tipped (sometimes weakly thorn-tipped in C. oliganthus); shrubs deciduous, semideciduous, or evergreen   (6)
2 (1) Leaf blades pinnately veined, adaxial surfaces green, shiny, abaxial surfaces pale green.   10 Ceanothus spinosus (in part)
+ 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 (2) Leaf blades 20–60 × 10–30 mm, abaxial surfaces pale green, appressed-puberulent, glabrescent, adaxial surfaces grayish green, glabrate.   12 Ceanothus incanus (in part)
+ 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 (3) Shrubs 1.5–4 m, stems erect; inflorescences usually paniclelike, sometimes racemelike, (3–)5–15 cm.   11 Ceanothus leucodermis
+ Shrubs 0.5–1.5 m, stems erect, ascending, or spreading; inflorescences umbel-like or racemelike, 1–3.5(–4) cm   (5)
5 (4) Stems ascending to spreading, not rooting at nodes; leaf blade adaxial surfaces pale to grayish green, glabrate.   13 Ceanothus cordulatus
+ Stems erect, ascending, or spreading, rooting at proximal nodes; leaf blade adaxial surfaces dark green, appressed villosulous or glabrous.   14 Ceanothus fendleri
6 (1) Leaf blades pinnately veined (proximal pair of secondary veins rarely more prominent and longer than distal pairs)   (7)
+ Leaf blades 3-veined from base (proximal pair of secondary veins longer than those above, sometimes equaling central vein)   (20)
7 (6) Leaf blade margins usually entire, rarely denticulate distally, adaxial surfaces glabrous or weakly puberulent   (8)
+ 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)
8 (7) Shrubs 0.3–0.8 m; inflorescences usually umbel-like, sometimes racemelike   (9)
+ Shrubs 1–3 m; inflorescences racemelike to paniclelike   (10)
9 (8) Sepals, petals, and nectaries white; petioles 0.5–1 mm.   4 Ceanothus microphyllus (in part)
+ Sepals, petals, and nectaries blue; petioles 1–3 mm.   26 Ceanothus foliosus (in part)
10 (8) Shrubs deciduous; leaf blades flat   (11)
+ Shrubs evergreen or semideciduous; leaf blades ± cupped   (12)
11 (10) Leaf blades 6–25 mm, adaxial surfaces ± shiny; capsules usually not lobed, sometimes weakly lobed.   7 Ceanothus parvifolius (in part)
+ Leaf blades 20–80 mm, adaxial surfaces dull; capsules lobed.   8 Ceanothus integerrimus (in part)
12 (10) Sepals and petals usually white, rarely pale blue; capsules lobed, valves viscid, crested; leaf blade adaxial surfaces dull to ± shiny.   9 Ceanothus palmeri
+ Sepals and petals pale blue to blue; capsules not lobed, valves not conspicuously viscid, not or weakly crested; leaf blade adaxial surfaces shiny.   10 Ceanothus spinosus (in part)
13 (7) Leaf blade margins not revolute   (14)
+ Leaf blade margins revolute   (16)
14 (13) Shrubs 0.2–0.3(–0.5) m; stems spreading; capsules 4–5 mm wide; leaf blade surfaces pilosulous.   28 Ceanothus diversifolius
+ Shrubs 1–3.5 m; stems erect to ascending; capsules 3–4 mm wide; leaf blade surfaces villosulous to strigillose or glabrate   (15)
15 (14) Branchlets green; petiole 1–3 mm; leaf blade margins usually wavy, sometimes not.   26 Ceanothus foliosus (in part)
+ Branchlets pale green to grayish green and glaucous; petiole 2–8 mm; leaf blade margins not wavy.   27 Ceanothus lemmonii (in part)
16 (13) Branchlets lanate to woolly, glabrescent; leaf blade abaxial surfaces cobwebby, soon glabrescent; inflorescences paniclelike, 5–15 cm.   19 Ceanothus parryi (in part)
+ 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 (16) Leaf blade adaxial surfaces strigillose or sparsely puberulent, not glandular papillate   (18)
+ Leaf blade adaxial surfaces glandular-papillate, sometimes also puberulent or villosulous   (19)
18 (17) Leaf blades oblong, elliptic, or suborbiculate, 6–25 × 4–15 mm, adaxial surfaces sparsely puberulent, veins furrowed.   22 Ceanothus impressus
+ Leaf blades narrowly elliptic, narrowly oblong, or linear, 5–16 × 2–8 mm, adaxial surfaces strigillose, veins not furrowed.   23 Ceanothus dentatus
19 (17) Shrubs 1–5 m; stems erect to ascending; leaf blades 12–50 × 6–15 mm; capsules 2–3 mm wide.   24 Ceanothus papillosus
+ 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.   25 Ceanothus hearstiorum
20 (6) Leaf blade margins usually entire, rarely denticulate or serrulate distally   (21)
+ Leaf blade margins serrate, serrulate, or denticulate (rarely entire in C. cyaneus)   (25)
21 (20) Petioles 0.5–1 mm; leaves often fascicled, blades 2–10 × 1–6 mm; se United States.   4 Ceanothus microphyllus (in part)
+ Petioles (1–)1.5–12 mm; leaves not fascicled, blades 6–80 × 3–45 mm; w United States   (22)
22 (21) Branchlets light gray; capsules prominently rugose.   12 Ceanothus incanus (in part)
+ Branchlets pale green or green to grayish green or brown; capsules smooth to ± rugulose   (23)
23 (22) 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.   6 Ceanothus martini (in part)
+ 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 (23) Leaf blades 6–25 mm, adaxial surfaces ± shiny; capsules usually not lobed, sometimes weakly lobed.   7 Ceanothus parvifolius (in part)
+ Leaf blades (10–)20–80 mm, adaxial surfaces dull; capsules lobed.   8 Ceanothus integerrimus (in part)
25 (20) 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)
+ 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)
26 (25) Leaf blades leathery, resinous, aromatic, adaxial surfaces shiny.   5 Ceanothus velutinus
+ Leaf blades herbaceous, not resinous, not aromatic, adaxial surfaces dull   (27)
27 (26) Leaf blades usually elliptic to lanceolate, sometimes ovate or oblanceolate; inflorescences terminal, globose to hemispheric.   2 Ceanothus herbaceus
+ Leaf blades ovate, oblong-ovate, or widely elliptic; inflorescences terminal or axillary, cylindric to conic   (28)
28 (27) Shrubs evergreen; branchlets brown, tomentulose; sepals, petals, and nectaries blue; California Channel Islands.   15 Ceanothus arboreus
+ 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 (28) Leaf blade apices usually acuminate to acute, rarely obtuse; capsules not lobed, valves ± rugulose, crested; e North America.   1 Ceanothus americanus
+ Leaf blade apices acute to rounded; capsules weakly lobed near apex, valves smooth, not or sometimes weakly crested; w North America (disjunct in Michigan).   3 Ceanothus sanguineus
30 (25) Leaf blade margins revolute   (31)
+ Leaf margins not revolute (sometimes incompletely revolute in C. thyrsiflorus)   (32)
31 (30) Branchlets usually round, sometimes ± angled, in cross section, lanate to woolly, glabrescent; leaf blade abaxial surfaces cobwebby, soon glabrescent.   19 Ceanothus parryi (in part)
+ Branchlets angled in cross section, sparsely puberulent or glabrous; leaf blade abaxial surfaces puberulent to villosulous.   21 Ceanothus griseus
32 (30) Branchlets angled in cross section   (33)
+ Branchlets round in cross section (rarely angled in cross section in C. oliganthus)   (34)
33 (32) Branchlets often tuberculate (tubercles minute, brownish); inflorescences 15–30(–40) cm, paniclelike; capsules deeply lobed.   18 Ceanothus cyaneus
+ Branchlets not tuberculate; inflorescences 2.5–9 cm, usually racemelike, rarely paniclelike; capsules weakly lobed.   20 Ceanothus thyrsiflorus
34 (32) Sepals and petals white, nectaries pale yellow to yellow-green; leaf blade margins serrulate distal to middle.   6 Ceanothus martini (in part)
+ 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 (34) Branchlets reddish brown to brown; leaf blades ovate to widely elliptic   (36)
+ Branchlets green, pale green, or grayish green; leaf blades narrowly elliptic, oblong-elliptic, or oblanceolate   (37)
36 (35) Leaf blade abaxial surfaces glabrate to hirtellous; petiole 3–8 mm; capsules 4–7 mm wide.   16 Ceanothus oliganthus
+ Leaf blade abaxial surfaces tomentose to tomentulose; petiole 1–4 mm; capsules 3–4 mm wide.   17 Ceanothus tomentosus
37 (35) Branchlets green; leaf blades ± folded lengthwise, margins usually ± wavy, sometimes not; capsule valves not or weakly crested.   26 Ceanothus foliosus (in part)
+ Branchlets pale green to grayish green and glaucous; leaf blades flat, margins not wavy; capsule valves crested.   27 Ceanothus lemmonii (in part)

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