Full text key to N. American species of Ceanothus
Key to Subgenera
1. Stipules thin, deciduous; leaves alternate, evergreen or deciduous,
usually thin, bases 1 or
3-veined - C. subgenus Ceanothus.
1. Stipules thick, persistent, usually corky; leaves opposite (alternate
in C. verrucosus,C.
megacarpus, and some C. insularis), evergreen, usually thickened, bases
1-veined. - C. subgenus Cerastes.
Ceanothus subg. Ceanothus Weberbauer Nat. Pflanzenfam. 3(5): 414. 1896
Ceanothus sect. Euceanothus A. P. De Condolle Prodromus systematis regni vegetabilis, Part II, pp. 29-33, Paris 1825.
Weberbauer Nat. Pflanzenfam. 3(5): 413--414. 1896 also recognized sect. Americani (Americanae), sect. incani (Incanae), sect. Sorediati (Sorediatae), sect. Thyrsiflori (Thyrsiflorae), sect Integerrimi (Integerrimae), sect. Microphylli (Microphyllae) A
C. section Euceanothus A. P. De Condolle Prodromus systematis regni vegetabilis, Part II, pp. 29-33, Paris 1825.
Key to the species of Ceanothus subg. Ceanothus
1. Twigs spinescent
2. Leaf blades 1-veined from base - C.
2. Leaf blades 3-veined from base; the two lateral veins may be
3. Leaf blades 2.5--6.5 cm long, glabrous or +/-
sides, petioles 4--12 mm long; flowers white; Outer Coast Ranges from San
Francisco Bay region n., Calif - C. incanus
3. Leaf blades usually 1.0--2.5 cm long, usually not glabrous both sides, petioles 2--6 mm long.
4. Erect shrubs to 4 m; inflorescences 2.5--7.5 cm
pale blue to white; Calif. Sierra Nevada foothills, Coast Ranges from San
Francisco s. to Baja, Calif - C.
4. Spreading to erect shrubs to 2.5 m; inflorescences to 3.9 cm long; flowers white.
5. Shrubs to 1.5; stems spreading; leaves adaxially
glaucous appearing light to gray-green, glabrous to puberulent, plane to
troughed; Calif., Nev., Oreg.; Mexico in Baja California - C. cordulatus
5. Shrubs to 2.5 m; stems low-spreading to erect; leaves
adaxially dark green, appressed silky hairs or nearly glabrous,
plane; Ariz., Colo, N.Mex., S.Dak., Tex., Utah, Wyo; Mexico in
Chihuahua, Coahila. - C. fendleri
1. Twigs flexible or rigid, but not spinescent
6. Leaf blades 1-veined from base, sometimes the basal,
lateral pair may be more prominent and longer than other laterals.
7. Leaf blade margins entire or sometimes toothed near
the tips, adaxial surface glabrous, flowers white to blue
6. Leaf blades 3-veined from base; the two lateral pair may not be as well developed as the midvein.
8. Leaves evergreen, margins entire; flowers white to
7. Leaf blade margins variously toothed, pubescent especially the adaxial surface, flowers blue.
9. Leaf blade tips rounded to notched; flowers white;
fruit prominently 3-lobed, 5--7 mm broad, smooth, horns 0, valves
glandular-crested - C. palmeri
8. Leaves deciduous, margins usually entire or minutely toothed towards tip; flowers white or pale to deep blue, rarely pink.
9. Leaf blade tips obtuse to notched; flowers pale blue to +/-
white; fruits globose, 4--5 mm broad, smooth, horns 0 ; valve crests
minute or 0. - C. spinosus
10. Shrubs low, ascending to 1.0 m; leaves 0.6--2.5
cm, bases cuneate, petioles to 5 mm; flowers pale to deep blue -
10. Shrubs ascending-erect to 4.0 m; leaves 2.5-- 8.0 x 1.0--3.9
cm, bases round, petioles to 15 mm; flowers white, pale to dark
blue, rarely pink - C. integerrimus
11. Leaf margins revolute, not undulate.
12. Twigs angled; tips obtuse, adaxially dark,
green, hirsute or villous, plane; inflorescences panicle-like,
5.0--15.0 cm - C. parryi
11. Leaf margins not revolute, often undulate.
12. Twigs not angled, inflorescences to 5.0 cm long.
13. leaf blades adaxially glandular-papillate.
abaxially dark green, cobwebby, usually densely hairy, adaxially
+/- convex; fruit valve crests minute. - C. papillosus
13. leaf blades adaxially not glandular-papillate,
14. Leaves abaxially pale green, gray-tomentose, adaxially
plane or +/- concave; fruit valve crests 0 - C. hearstiorum
15. blades ovate to +/- round; 0.6--2.5 x
-1.2, petioles to 4 mm; fruit valve crests prominent - C. impressus
15. blades elliptic to narrowly oblong or linear,
0.5--1.5 (2.5) x 0.2--1.3 cm; fruit valve crests minute - C. dentatus
16. Shrubs +/- trailing to 3 dm; twigs rough,
petioles to 13 mm, margins serrate or denticulate, glands few,
adaxially bluish-green, pubescent; fruit valves crested, toward
apex. - C. diversifolius
16. Shrubs low-spreading to erect 0.3--2.5 m; leaves variously green, not bluish-green, petioles less than 8 mm.
17. Leaf petioles to 3 mm, adaxially dull to
green, glabrous, waxy, or puberulent, +/- plane, undulate or occasionally troughed; fruit valves +/- crested. Calif. from outer N. Coastal Range (Humboldt Co.) south
to Peninsular Ranges (San Diego Co.) -
17. Leaf petioles 2--8 mm, adaxially dull green, +/-
glabrous to strigose, plane; fruit valves prominently crested.
Calif. inner N. Coastal Range; foothills of Cascade Range &
Sierra Nevada - C.
18. Leaf margins usually entire, occasionally
toothed towards apex, deciduous or semideciduous; flowers white or blue.
19. Leaves usually clustered, thickened, usually
less than 6
mm wide, elliptical, elliptic-ovate or obovate, petioles 0.5--1 mm;
flowers white; fruit valve crests 0; Fla., s. Ga., se Ala - C. microphyllus 18. Leaf margins serrate, serrulate, or glandular toothed, evergreen or deciduous.
19. Leaves not
clustered, not thickened, more than 6 mm wide,
petioles more than 1 mm.
20. Leaves more than 2.5 cm long; inflorescences
cm; flowers white, pale to dark blue, rarely pink; fruits sticky,
valves minutely crested. Ariz, Calif., N.Mex., Oreg., Wash. - C. integerrimus
20. Leaves less than 2.5 cm.
21. flowers dull white; inflorescences 1.5--3.0
fruit valves crested; leaf blades oval, approaching orbicular, rarely elliptic or obovate, abaxially light green, pubescent on veins, occasionally over entire surface;
Ariz., Colo., Nev., Utah, Wyo. - C.
21. Flowers pale to deep blue; inflorescences 2.5-- 7.5
cm; fruit valve crests +/- 0; leaf blades oblong-elliptic to
elliptic, abaxially pale green, rarely pubescent; Calif. - C. parvifolius
22. Leaves deciduous; flowers white.
23. Leaf blades less than 2.2 cm, oval,
orbicular, rarely elliptic or obovate; Ariz., Colo., Nev., Utah,
Wyo. - C. martinii
22. Leaves evergreen; flowers white or blue.
23. Leaf blades more than 2.2 cm, not approaching orbicular.
24. Shrubs to 3 m; twigs glabrous, rigid;
petioles 6--25 mm - C. sanguineus
24. Shrubs to 1.5 m; twigs pubescent, flexible; leaf petioles 2--13 mm
25. twigs green; leaf petioles 4--13
inflorescences terminal or axillary, 3.0--10.0 cm. - C. americanus
25. twigs brown or purplish; leaf petioles 2--6 mm;
inflorescences terminal, usually 1.5--3.0 cm. - C. herbaceus
26. Twigs rigid, sometimes +/- spinescent.
27. Twigs not spinescent; flowers white,
leaves to 13 cm
long, adaxially glabrous, +/- varnished. - C.
26. Twigs flexible, not spinescent.
27. Twigs +/- spinescent; flowers pale to deep blue;
leaves to 3.8 cm long, adaxially pubescent, or +/- glabrous, not
varnished. - C. oliganthus var.
28. Twigs round.
29. Shrubs to 7 m; leaf petioles 8--20
mm; blades to
7.5 cm; fruits 6--8 mm broad - C. arboreus
28. Twigs angled.
29. Shrubs usually to 3 m; leaf petioles to 8 mm; blades to 3.8 cm; fruits +/- 4 mm broad.
30. Twigs rusty tomentose or not,
tuberculate; leaves usually glandular-serrate or glandular-dentate, abaxially whitish or brownish tomentose or pubescent; flowers azure-blue to nearly
white. - C.tomentosus
30. Twigs +/- glabrous, puberulent or villous;
leaves minutely gland-toothed, abaxially glabrous or with
scattered long hairs; flowers deep blue or purplish tinged,
to nearly white. - C.
31. Leaf margins revolute, sometimes slightly
32. Leaves adaxially dark green,
glabrous, plane or
+/- convex; inflorescences 1.9-- 5.0 cm; flowers blue; fruits
glandular- sticky when young, shiny when mature. - C. griseus
31. Leaf margins not revolute.
32. Leaves adaxially dark, shiny green, hirsute or
villous, plane; inflorescences 5.0--15.0 cm. flowers deep blue;
fruits smooth. - C. parryi
33. twigs light green, roughened
brownish glands, glabrous to puberulent; leaf petioles 3--6
mm; inflorescences 10.0--30.0 cm. - C. cyaneus
33. twigs green, smooth, glabrous, leaf petioles
to 3--13 mm; inflorescences 2.5-- 8.0 cm. -