Flora of North America species comparison

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Ceanothus cordulatus

Ceanothus sonomensis

mountain whitethorn, snow bush, whitethorn ceanothus

Sonoma ceanothus
Habit Shrubs, evergreen, 0.5–1.5 m. Stems ascending to spreading, not rooting at nodes; branchlets yellowish or grayish green, glaucescent, thorn-tipped, round in cross section, rigid, puberulent, glabrescent. Shrubs, 0.5–1 m, often moundlike.
Stems

erect to ascending, not rooting at nodes;

branchlets gray to grayish brown, rigid, strigillose, glabrescent.
Leaves

petiole 2–8 mm;

blade flat to cupped, ovate to elliptic, 10–30 × 6–18 mm, base rounded, margins usually entire, sometimes minutely glandular-denticulate distally, glands 18–30, apex obtuse, abaxial surface pale grayish green, sparsely puberulent or glabrous, sometimes villosulous along veins, adaxial surface pale green to grayish green, glaucous, dull, glabrate; 3-veined from base.

not fascicled;

petiole 0–1 mm;

blade cupped, widely obovate to suborbiculate, 5–12 × 2–10 mm, base cuneate, margins not revolute, wavy, spinose-dentate, teeth 2–4, apex widely notched;

abaxial surface pale green or grayish green and glaucous, strigillose on veins, adaxial surface shiny green, glabrous.
Inflorescences

axillary, umbel-like or racemelike, sometimes densely clustered, 1.2–2(–4) cm.

axillary or terminal, 0.8–1.5 cm.
Flowers

sepals, petals, and nectary usually white, rarely pink.

sepals, petals, and nectary blue to lavender.
Capsules

3.5–5 mm wide, lobed;

valves rugose, viscid when young, weakly crested.

4–5 mm wide, usually not, sometimes weakly lobed;

valves smooth, horns subapical, minute to ± prominent, erect, intermediate ridges absent.
2n

= 24.

= 24.

Ceanothus cordulatus

Ceanothus sonomensis
Phenology Flowering May–Jul. Flowering Mar–Apr.
Habitat Rocky ridges and slopes, chaparral, conifer and mixed evergreen forests. Sandy to rocky soils derived mostly from volcanic substrates, slopes, ridges, chaparral.
Elevation 400–3400 m. (1300–11200 ft.) 100–700 m. (300–2300 ft.)
Distribution
from FNA
CA; NV; OR; Mexico (Baja California)
[WildflowerSearch map]
[BONAP county map]
from FNA
CA
[BONAP county map]
Discussion

Ceanothus cordulatus is one of the most common shrubs in montane chaparral and forests of the Coast Ranges and Cascades of southern Oregon and northern California, southward through the Sierra Nevada, Transverse and Peninsular ranges of California, to the mountains of northern Baja California, and occurs disjunctly in the Charleston Mountains of Nevada.

Putative hybrids between Ceanothus cordulatus and C. velutinus var. velutinus, reported from the Klamath Mountains, the southern Cascade Range, and the Sierra Nevada, have been called C. ×lorenzenii (Jepson) McMinn. A rare intersectional hybrid between C. cordulatus and C. prostratus in the Lake Tahoe basin has been named C. ×serrulatus McMinn. Putative hybrids of C. cordulatus with C. diversifolius and C. integerrimus also have been reported (H. McMinn 1944).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Ceanothus sonomensis is distinctive in having spinose-dentate, few-toothed leaves, and slender fruit horns two to three millimeters; it occurs at a few scattered localities in the mountains of Napa and Sonoma counties.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 12, p. 87. FNA vol. 12, p. 103.
Parent taxa Rhamnaceae > Ceanothus > subg. Ceanothus Rhamnaceae > Ceanothus > subg. Cerastes
Sibling taxa
C. americanus, C. arboreus, C. arcuatus, C. confusus, C. crassifolius, C. cuneatus, C. cyaneus, C. dentatus, C. divergens, C. diversifolius, C. fendleri, C. ferrisiae, C. foliosus, C. fresnensis, C. gloriosus, C. griseus, C. hearstiorum, C. herbaceus, C. impressus, C. incanus, C. integerrimus, C. jepsonii, C. lemmonii, C. leucodermis, C. maritimus, C. martini, C. masonii, C. megacarpus, C. microphyllus, C. oliganthus, C. ophiochilus, C. otayensis, C. palmeri, C. papillosus, C. parryi, C. parvifolius, C. pauciflorus, C. perplexans, C. pinetorum, C. prostratus, C. pumilus, C. purpureus, C. roderickii, C. sanguineus, C. sonomensis, C. spinosus, C. thyrsiflorus, C. tomentosus, C. velutinus, C. verrucosus
C. americanus, C. arboreus, C. arcuatus, C. confusus, C. cordulatus, C. crassifolius, C. cuneatus, C. cyaneus, C. dentatus, C. divergens, C. diversifolius, C. fendleri, C. ferrisiae, C. foliosus, C. fresnensis, C. gloriosus, C. griseus, C. hearstiorum, C. herbaceus, C. impressus, C. incanus, C. integerrimus, C. jepsonii, C. lemmonii, C. leucodermis, C. maritimus, C. martini, C. masonii, C. megacarpus, C. microphyllus, C. oliganthus, C. ophiochilus, C. otayensis, C. palmeri, C. papillosus, C. parryi, C. parvifolius, C. pauciflorus, C. perplexans, C. pinetorum, C. prostratus, C. pumilus, C. purpureus, C. roderickii, C. sanguineus, C. spinosus, C. thyrsiflorus, C. tomentosus, C. velutinus, C. verrucosus
Name authority Kellogg: Proc. Calif. Acad. Sci. 2: 124, fig. 39. (1863) J. T. Howell: Leafl. W. Bot. 2: 162. (1939)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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