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.


Subgenus: Ceanothus

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 pparently valid.

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. spinosus
2. Leaf blades 3-veined from base; the two lateral veins may be somewhat obscure.
3. Leaf blades 2.5--6.5 cm long, glabrous or +/- puberulent both 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 long, flowers pale blue to white; Calif. Sierra Nevada foothills, Coast Ranges from San Francisco s. to Baja, Calif - C. leucodermis
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
8. Leaves evergreen, margins entire; flowers white to pale 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
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
8. Leaves deciduous, margins usually entire or minutely toothed towards tip; flowers white or pale to deep blue, rarely pink.
10. Shrubs low, ascending to 1.0 m; leaves 0.6--2.5 x 0.3--1.3 cm, bases cuneate, petioles to 5 mm; flowers pale to deep blue - C. parvifolius
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
7. Leaf blade margins variously toothed, pubescent especially the adaxial surface, flowers blue.
11. Leaf margins revolute, not undulate.
12. Twigs angled; tips obtuse, adaxially dark, shiny green, hirsute or villous, plane; inflorescences panicle-like, 5.0--15.0 cm - C. parryi
12. Twigs not angled, inflorescences to 5.0 cm long.
13. leaf blades adaxially glandular-papillate.
14. Leaves abaxially dark green, cobwebby, usually densely hairy, adaxially +/- convex; fruit valve crests minute. - C. papillosus
14. Leaves abaxially pale green, gray-tomentose, adaxially plane or +/- concave; fruit valve crests 0 - C. hearstiorum
13. leaf blades adaxially not glandular-papillate,
15. blades ovate to +/- round; 0.6--2.5 x 0.4- -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
11. Leaf margins not revolute, often undulate.
16. Shrubs +/- trailing to 3 dm; twigs rough, hairy; leaf 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 dark 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.) - C. foliosus
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. lemmonii
6. Leaf blades 3-veined from base; the two lateral pair may not be as well developed as the midvein.
18. Leaf margins usually entire, occasionally minutely 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
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 4.0-- 15.0 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 cm.; 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. martinii
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
18. Leaf margins serrate, serrulate, or glandular toothed, evergreen or deciduous.
22. Leaves deciduous; flowers white.
23. Leaf blades less than 2.2 cm, oval, approaching orbicular, rarely elliptic or obovate; Ariz., Colo., Nev., Utah, Wyo. - C. martinii
23. Leaf blades more than 2.2 cm, not approaching orbicular.
24. Shrubs to 3 m; twigs glabrous, rigid; leaf 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 mm; 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
22. Leaves evergreen; flowers white or blue.
26. Twigs rigid, sometimes +/- spinescent.
27. Twigs not spinescent; flowers white, leaves to 13 cm long, adaxially glabrous, +/- varnished. - C. velutinus
27. Twigs +/- spinescent; flowers pale to deep blue; leaves to 3.8 cm long, adaxially pubescent, or +/- glabrous, not varnished. - C. oliganthus var. sorediatus
26. Twigs flexible, not spinescent.
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
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, sometimes densely 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. oliganthus
28. Twigs angled.
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
32. Leaves adaxially dark, shiny green, hirsute or villous, plane; inflorescences 5.0--15.0 cm. flowers deep blue; fruits smooth. - C. parryi
31. Leaf margins not revolute.
33. twigs light green, roughened with scattered 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. - C.thyrsiflorus