Flora of North America species comparison

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Ceanothus cordulatus

Ceanothus jepsonii

mountain whitethorn, snow bush, whitethorn ceanothus

Jepson ceanothus, Jepson's ceanothus, musk brush
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, 0.5–1.5 m. Stems erect to ascending, not rooting at nodes; branchlets reddish to grayish brown, rigid, puberulent, 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, deflexed;

petiole 0–2 mm;

blade ± cupped, slightly folded lengthwise adaxially, elliptic to ± oblong, 10–20 × 5–13 mm, base rounded, margins thick or slightly revolute, spinose-dentate, teeth 7–11, apex rounded or sharply acute, abaxial surface pale yellowish green, glabrous, adaxial surface pale green, glabrous.
Inflorescences

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

axillary or terminal, 1–2 cm.
Flowers

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

sepals and petals (5–)6(–8), usually blue to lavender or white, rarely pink;

nectary blue;

stamens (5–)6(–8).
Capsules

3.5–5 mm wide, lobed;

valves rugose, viscid when young, weakly crested.

5–7 mm wide, lobed;

valves rugose, horns subapical, prominent, thick, erect, rugose, intermediate ridges present.
2n

= 24.

Ceanothus cordulatus

Ceanothus jepsonii
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
[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).

Ceanothus jepsonii, composed of two, allopatric varieties, is the only species with mostly six (rarely eight) sepals and petals, and cymules reduced to solitary flowers (M. A. Nobs 1963). T. M. Hardig et al. (2000) provided evidence showing that the two varieties may not form a monophyletic group. H. McMinn (1942) and Nobs (1963) reported putative hybrids with C. cuneatus and C. prostratus.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Sepals and petals usually pale blue to lavender, rarely pink or white; capsules globose.
var. jepsonii
1. Sepals and petals white; capsules ± oblong.
var. albiflorus
Source FNA vol. 12, p. 87. FNA vol. 12, p. 106.
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. 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
Subordinate taxa
C. jepsonii var. albiflorus, C. jepsonii var. jepsonii
Name authority Kellogg: Proc. Calif. Acad. Sci. 2: 124, fig. 39. (1863) Greene: Man. Bot. San Francisco, 78. (1894)
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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