Jepson eFlora: Taxon page
Vascular Plants of California
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Ceanothus sonomensis

Higher Taxonomy
Family: RhamnaceaeView DescriptionDichotomous Key

Habit: [Perennial herb] shrub, tree, generally erect, often thorny. Leaf: simple, generally alternate, often clustered on short-shoots; stipules generally present, occasionally modified into spines; generally petioled; blade pinnate-veined or 1--5-ribbed from base. Inflorescence: cyme, panicle, umbel, or flowers 1 or clustered in axils or on short-shoots. Flower: generally bisexual, radial; hypanthium subtending, surrounding, or partly fused to ovary; sepals 4--5; petals 0, 4--5, generally clawed; stamens 0, 4--5, alternate sepals, attached to hypanthium top, each generally fitting into a petal concavity; disk (0 or) between stamens, ovary, thin to fleshy, entire or lobed, free from ovary, adherent or fused to hypanthium; ovary superior or +- inferior, chambers [1]2--4, 1--2-ovuled, style 1, stigma entire or 2--3-lobed. Fruit: capsule, drupe.
Genera In Family: 50--52 genera, 950 species: especially tropics, subtropics some cultivated (Ceanothus; Frangula; Rhamnus; Ziziphus).
eFlora Treatment Author: John O. Sawyer, Jr., except as noted
Scientific Editor: Steve Boyd, Thomas J. Rosatti.
Ceanothus sonomensis J.T. Howell
Habit: Plant erect, +- open, < 1.5 m. Stem: ascending to erect, not rooting at nodes; twigs not angled; gray to brown. Leaf: opposite, evergreen, +- spreading; stipules knob-like; petiole < 1 mm; blade generally 5--11 mm, 2--5 mm wide, obovate to round, adaxially shiny green, glabrous, abaxially gray, minutely appressed-tomentose, especially veins, tip notched, margin thick, teeth 3--5, +- spine-like. Inflorescence: umbel-like, +- 1 cm. Flower: blue or lavender. Fruit: 4--5 mm wide; horns 2--3 mm, slender. Chromosomes: 2n=24.
Ecology: Serpentine or volcanic substrates, chaparral; Elevation: 140--600 m. Bioregional Distribution: NCoRO (Hood Mtn region, Sonoma and Napa cos.). Flowering Time: Mar--Apr Note: Occasionally confused with Ceanothus divergens.
Jepson eFlora Author: Dylan O. Burge & Dieter H. Wilken
Reference: Fross & Wilken 2006 Ceanothus. Timber Press; Burge et al. 2015 Syst Bot 40:950--961.
Index of California Plant Names (ICPN; linked via the Jepson Online Interchange)
Listed on CNPS Rare Plant Inventory

Previous taxon: Ceanothus sanguineus
Next taxon: Ceanothus spinosus

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Botanical illustration including Ceanothus sonomensis

botanical illustration including Ceanothus sonomensis

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Citation for this treatment: Dylan O. Burge & Dieter H. Wilken 2020, Ceanothus sonomensis, in Jepson Flora Project (eds.) Jepson eFlora, Revision 8,, accessed on October 03, 2023.

Citation for the whole project: Jepson Flora Project (eds.) 2023, Jepson eFlora,, accessed on October 03, 2023.

Ceanothus sonomensis
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© 2011 Vernon Smith
Ceanothus sonomensis
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© 2015 Barry Breckling
Ceanothus sonomensis
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© 2015 Barry Breckling

More photos of Ceanothus sonomensis in CalPhotos

Geographic subdivisions for Ceanothus sonomensis:
NCoRO (Hood Mtn region, Sonoma and Napa cos.).
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map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).


Data provided by the participants of the  Consortium of California Herbaria.
View all CCH records
All markers link to CCH specimen records. The original determination is shown in the popup window.
Blue markers indicate specimens that map to one of the expected Jepson geographic subdivisions (see left map). Purple markers indicate specimens collected from a garden, greenhouse, or other non-wild location.
Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues.

CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa, if there are more than 1 infraspecific taxon in CA.
Blue line denotes eFlora flowering time (fruiting time in some monocot genera).