SafePlants

Hairy Ceanothus (Ceanothus oliganthus)

Ceanothus oliganthus, commonly known as Hairy Ceanothus or Hairy-leaf Ceanothus, is a shrub belonging to the buckthorn family (Rhamnaceae). It is celebrated for its vibrant blue flowers that can carpet entire hillsides in spring.

Taxonomy and Nomenclature

• Scientific Name: Ceanothus oliganthus Nutt.
• Common Names: Hairy Ceanothus, Hairy-leaf Ceanothus, California Lilac, Soap Plant, Wild Lilac, Hairy Whitethorn
• Family: Rhamnaceae (Buckthorn Family)
• Taxonomic Rank: Species, Variety (e.g., Ceanothus oliganthus var. oliganthus)
• Synonyms:
  • Ceanothus divaricatus Nutt.
  • Ceanothus hirsutus Nutt.
  • Ceanothus orcuttii Parry.

Distribution and Habitat

• Ceanothus oliganthus is native to California and endemic to the state, meaning it is only found there.
• It is commonly found in central to southern California, particularly in inland chaparral environments.
• Specifically mentioned locations include coastal southern California on north-facing slopes, Sea Ranch, Oso Ridge, and the Santa Monica Mountains (Circle X Ranch, Mishe Mokwa trail).
• Also found in Oregon and Baja California, Mexico

Morphological Characteristics

• Hairy Ceanothus is typically a shrub ranging from 3 to 9 feet tall, though it can sometimes develop a tree-like trunk.
• It features flexible, hairy branchlets and twigs.
• The leaves are alternate and can be ovate or elliptic in shape.
• It is an erect evergreen shrub.

Ecological Role

• Ceanothus species can form impenetrable thickets, especially after fires in chaparral ecosystems.
• The plant's stems become woody with age in the absence of fire or browsing from animals.

Interactions with Other Organisms

• The plant is known to host insects, including hairy caterpillars (e.g., Hemileuca eglanterina on Ceanothus palmeri).
• Insect eggs are sometimes found under the gland-tipped leaves.

Further Information

• California Native Plant Society (San Diego Chapter): WWW.CNPSSD.ORG
• Dave's Garden
• Discover Life