Taxon Report

Ceanothus sonomensis J.T. Howell

Sonoma ceanothus

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Taxon Summary

Ceanothus sonomensis, commonly known as Sonoma ceanothus, is a perennial evergreen shrub in the Rhamnaceae that is found only in California. It occurs within Chaparral (sandy, serpentinite, and volcanic), growing at elevations from 215 to 800 meters. Ceanothus sonomensis is ranked 1B.2, Plants Rare, Threatened or Endangered in California and Elsewhere; Moderately threatened in California.


  Classification

Scientific Name:
Ceanothus sonomensis J.T. Howell
Common Name:
Sonoma ceanothus
Family: Rhamnaceae
Element Code: PDRHA04420
USDA Plants Symbol: CESO
Synonyms/Other Names:

Ecology and Life History

Lifeform: perennial evergreen shrub
Blooming Period: Feb-Apr Feb-Apr
Elevation: 215-800 (705-2625)
General Habitats: Chaparral
Microhabitat:
Microhabitat Details:

Occurrence Data from the CNDDB

Total Occurrences: 30
Element Occurrence Ranks:
   Excellent (A) 3
   Good (B) 1
   Fair (C) 0
   Poor (D) 1
   None (X) 0
   Unknown (U) 25
California Endemic:  True
California Counties and Islands: Name (Code)
Lake (LAK), Napa (NAP), Sonoma (SON)
Quads: Name (Quad Code)
Aetna Springs (3812264), Calistoga (3812255), Chiles Valley (3812253), Detert Reservoir (3812265), Glen Ellen (3812235), Kenwood (3812245), Rutherford (3812244), Santa Rosa (3812246), Sonoma (3812234), St. Helena (3812254), Walter Springs (3812263)

Threat List Data from the CNDDB

Threat List Total: 4
EOs with Threat Listed: Total EOs % of EOs
3 10 %
Improper burning regime 2 6%
Other 1 3%
Road/trail construction/maint. 1 3%
Development 1 3%

Notes

Seriously threatened by habitat alteration and development. Closely related to C. cuneatus.
Threats:
Taxonomy:
Citation California Native Plant Society, Rare Plant Program. 2025. Rare Plant Inventory (online edition, v9.5.1). Website https://www.rareplants.cnps.org [accessed 15 March 2025].