Flora of North America species comparison

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Ceanothus cordulatus

Ceanothus tomentosus

mountain whitethorn, snow bush, whitethorn ceanothus

woolly leaf ceanothus, woolyleaf 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, evergreen, 1.5–2.5 m. Stems erect, rarely spreading, not rooting at nodes; branchlets reddish brown, not thorn-tipped, round in cross section, flexible, tomentulose, 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.

petiole 1–4 mm;

blade flat, ovate to widely elliptic, 10–25 × 5–12 mm, base obtuse to rounded, margins serrulate to denticulate most of length, not revolute, teeth 39–71, apex obtuse, abaxial surface light or gray-green, tomentose to tomentulose, adaxial surface dark green, villosulous or puberulent, glabrescent; usually 3-veined from base, rarely pinnately veined (veins sometimes obscured by indumentum).
Inflorescences

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

axillary or terminal, racemelike or paniclelike, 2–6 cm.
Flowers

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

sepals, petals, and nectary usually deep blue, sometimes pale blue.
Capsules

3.5–5 mm wide, lobed;

valves rugose, viscid when young, weakly crested.

3–4 mm wide, slightly lobed at apex;

valves smooth, viscid when young, crested.
2n

= 24.

Ceanothus cordulatus

Ceanothus tomentosus
Phenology Flowering May–Jul.
Habitat Rocky ridges and slopes, chaparral, conifer and mixed evergreen forests.
Elevation 400–3400 m. (1300–11200 ft.)
Distribution
from FNA
CA; NV; OR; Mexico (Baja California)
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; nw Mexico
[WildflowerSearch map]
[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.)

Varieties 2 (2 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaf blade abaxial surfaces uniformly and densely tomentulose, veins obscured; c Sierra Nevada, California.
var. tomentosus
1. Leaf blade abaxial surfaces sparsely to moderately tomentulose, veins ± evident; s California.
var. olivaceus
Source FNA vol. 12, p. 87. FNA vol. 12, p. 89.
Parent taxa Rhamnaceae > Ceanothus > subg. Ceanothus Rhamnaceae > Ceanothus > subg. Ceanothus
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. sonomensis, C. spinosus, C. thyrsiflorus, C. velutinus, C. verrucosus
Subordinate taxa
C. tomentosus var. olivaceus, C. tomentosus var. tomentosus
Name authority Kellogg: Proc. Calif. Acad. Sci. 2: 124, fig. 39. (1863) Parry: Proc. Davenport Acad. Nat. Sci. 5: 190. (1889)
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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