Buckbrush

Ceanothus cuneatus var. cuneatus
NATIVE

Description (Jepson, PlantID.net)

• Eudicotyledon
  • Eudicots are a major lineage of flowering plants; see family for general characteristics
• Buckthorn Family (Rhamnaceae)
• Evergreen shrub
• Leaves
  • Stiff and tough
  • Wedge-shaped to notched
  • Oppositely arranged (2 leaves at each junction with stem) and often clustered
  • Deeply veined
• Flowers
  • Inflorescence (flower arrangement) of small, tight clusters
  • Flower parts are in fives
    • 5 broad white sepals (usually green, outer flower parts) curl up toward the flower’s center
    • 5 slender white petals extend like paddles beyond the sepals, ending in a scoop-shaped bowl
      • Narrowed petal base is called a claw
    • 5 yellow-tipped stamens (male flower parts) are in line with the petals, which is an unusual flower pattern
  • Ovary is partly inferior (partly below the attachment of other flower parts)
• Fruit a round, 3-part capsule (a dry, multi-chambered fruit that splits open at maturity) with horns
• Height to ~9 ft.

Distribution

• Native to California
  • Grows in many habitats across the state, including chaparral, scrub, oak woodlands, and pine forests (League 2005)
  • 50-54% of plants occur on ultramafic soils, e.g. serpentine; see ultramafic affinity rankings (Calflora per Safford and Miller 2020)
  • See Calflora for statewide observations of this plant
• Outside California, grows from Oregon to northern Baja California, Mexico
• Grows at elevations to 7,000 ft.

Uses (San Mateo County Parks prohibits removal of any natural material)

• Wildlife
  • Larval food source (host) for several butterfly species, e.g. California tortoiseshell (Nymphalis californica), echo blue (Celastrina landon echo), pale swallowtail (Papillo eurymedon), and hedgerow hairstreak (Satyrium saeplum)
• Native people
  • Mixed the ground roots and bark with water to create a mouthwash for sore throats or mouth sores
  • Mashed the flowers and fruits to produce a soap
  • Ate the seeds of some Ceanothus species
  • Used young shoots in basketry, including cradleboards, winnowing and burden baskets, and twined seed beaters (Anderson 2005)
    • Plants were actively managed by burning and coppicing (repeated cutting to near ground level) to stimulate rapid growth of straight, flexible shoots
    • A single twined seed-beater required almost 200 plant shoots, a quantity that would require 400 unmanaged shrubs as compared to 16 managed shrubs

Name Derivation

• Ceanothus (see-a-NO-thus) – from the Greek for “spiny plant,” referring to the thorn-like branch ends
• cuneatus (kew-nee-AY-tus) – from the Latin for “wedge-shaped,” referring to the leaf shape (compare cuneiform, the early writing system using wedge-shaped characters)
• Buckbrush – the common name for several species of North American shrubs that deer feed on, but in western North America, it is specifically associated with C. cuneatus
• California lilac – a common name given to all Ceanothus species because of the similarity of the shape (especially in the subgenus Ceanothus) and smell of the inflorescence to the cultivated lilac (Syringa species) of southeast Europe and eastern Asia

Adaptations

• Aromatic flowers attract bees and other insects
• Component of California chaparral
  • Chaparral refers to evergreen shrub and small tree communities that grow on shallow, rocky, nutrient-poor soils in Mediterranean climates, with mild, wet winters and hot, dry summers
  • Chaparral shrubs, like buckbrush, are examples of sclerophyllous (“hard-leaf”) vegetation, with leaves that conserve water by being
    • Thick and leathery, with extra lignin (structural component that stiffens plant tissue) to prevent wilting
    • Waxy, with a thick cuticle that reduces transpiration
    • Densely organized, occurring at short distance along the stem, thus increasing local humidity
    • Usually small and oriented parallel or oblique to direct sunlight, reducing surface exposure
• A symbiotic relationship with nitrogen-fixing bacteria allows buckbrush to grow in nitrogen-poor soils
  • Buckbrush roots have nodules that host nitrogen-fixing bacteria (Rhizobium)
    • Bacteria capture nitrogen gas (N2) from the air (fixing it) and convert it into nitrogen compounds that plants can use
  • Host plant shares minerals and carbohydrates produced by photosynthesis with the bacteria
  • When the plant dies, the fixed nitrogen is released, fertilizing the surrounding soil for other plants
• Seeds have several adaptations for dispersal and germination
  • Mature fruit capsules will explode (League 2005)
    • Although the majority of seeds fall near the parent shrub, seeds may be cast up to 35 ft.
    • The explosive release of seeds from a fruit is called ballochory
  • Seeds can also be dispersed by insects
    • California harvester ants have been known to cache the seeds
  • Dormant seeds germinate after fire or other disturbance

Notes

• The genus Ceanothus has two subgenera
  • The Cerastus subgenus, which includes buckbrush, has
    • Generally opposite leaves, usually smaller and thicker, with a single main vein
    • Flowers in compact clusters
  • The Ceanothus subgenus, which includes blue blossom and Jim brush, has
    • Generally alternate leaves, usually larger and thinner, with three major veins
    • Flowers in elongated clusters
• Edgewood’s buckbrush is classified as a variety
  • Variety indicates a population with small morphological variations, e.g. color, seen throughout the geographic range of the species; interbreeding is possible
  • Subspecies indicates a geographically-separated population with distinct morphological characteristics; when not isolated, interbreeding is possible
  • In practice, botanists have not consistently applied these ranks

ID Tips

• May be confused with chaparral pea (Pickeringia montana), seen on the upper Clarkia trail, when flowers are not present
  • Buckbrush
    • Leaves are opposite (2 leaves at each junction with stem) and simple (not divided into leaflets)
    • Leaves dull green on top
    • Branches lack a terminal thorn
  • Chaparral pea
    • Leaves are alternate (1 leaf at each junction with stem) and compound (divided into leaflets), usually with 3 leaflets
    • Leaves shiny green on top
    • Branches have a terminal thorn

At Edgewood

• Found commonly in chaparral, though also occurs occasionally in coastal scrub and oak woodlands
  • See iNaturalist for observations of Ceanothus cuneatus
• Flowers February – August

See General References

Specific References

Anderson, M.K. 2005. Tending the Wild. University of California, Berkeley.

League, K.R. 2005. Ceanothus cuneatus. Fire Effects Information System. United States Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Safford, H.D. and J.E.D. Miller. 2020. An updated database of serpentine endemism in the California flora. Madroño 67(2): 85-104. BioOne Complete. PDF hosted by San Diego State University, San Diego, California.

Shapiro, A.M. and T.D. Manolis. 2007. Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions. University of California Press, Berkeley and Los Angeles, California.