Whitethorn Ceanothus Ceanothus cordulatus
Whitethorn Ceanothus is a perennial shrub native to the lower 48 states. It grows to 8 ft and blooms Jun in part shade – shade, with brown fruit.
More about this plant
Ceanothus cordulatus is a species of shrub in the family Rhamnaceae known by the common names mountain whitethorn and whitethorn ceanothus. It is native to California and adjacent sections of Oregon, Nevada, and Baja California, where it grows on mountain ridges and other forested areas. This is a spreading shrub growing usually wider than tall and up to about 1.5 meters. The stems are gray, with the twigs yellow-green in color and fuzzy in texture when new. The evergreen leaves are alternately arranged and up to 3 centimeters long. Each is oval in shape with three ribs and generally not toothed. The leaves may be hairy or not. The inflorescence is panicle-shaped, up to about 4 centimeters long. The flowers are white to off-white with five sepals and five petals. The fruit is a rough, ridged capsule up to half a centimeter long. It has three valves inside, each containing a seed. It is a nitrogen-fixing plant, that is uniquely abundant in old-growth forest conditions when compared to similar types of nitrogen-fixing plants. In addition, Ceanothus cordulatus is known to be an important source of nitrogen patches for significantly longer times than other similar post-disturbance successional shrubs, following disturbance events such as forest fires. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Part shade – shade
- Soil & moisture
- Low moisture
- Soil pH
- 7–8.5
- Fertility need
- Low
- Adapts to
- Coarse (sandy), Medium (loam)
- Hardiness
- USDA zone 5+
- Height
- 8 ft
- Mature width
- ~ 7 ft wide DERIVED derived estimate — open-grown crown allometry (height × growth-form ratio); not a measurement
- Spacing
- 4–8 ft apart from USDA planting density
- Spread
- None — clumping
- Growth rate
- Slow
- Growth form
- Multiple stems
- Lifespan
- Perennial · long-lived
- Foliage
- Broadleaf · fine texture
- Active growth
- Spring & summer
- Fruit
- Brown
- Flower colour
- White AI AI image-analysis of community-science photos (~87% expert agreement) — not a botanical record
- Propagate by
- Seed, Bare root, Container
- Seed starting
- No stratification needed
- Seeds ripen
- Summer – Autumn seed-collection / harvest window
- In the trade
- Routinely available
- Deer browsing
- High browsed readily
- Resprouts if cut
- Yes regrows after top-kill
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~45 caterpillar species
Ceanothus supports ~45 caterpillar species.
Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a strong genus.
Recorded feeding on Ceanothus in North America, including:
+ 8 more species → ↑ show fewer
✦ Bees 10 bee visitors
10 native & managed bee species are documented visiting Whitethorn Ceanothus :
Wildlife & visitors 11 nectaring
Open records of who else uses Whitethorn Ceanothus — a generalist food-web signal, kept separate from the keystone Ecological Value.
11 adult butterfly & moth species are recorded nectaring at its flowers — the most-recorded:
Related plants
More Ceanothus →
How we know this (4) Methods & honest limits
A recorded categorical fact: each species is tagged C3 (standard), C4 (heat/water-efficient) or CAM (succulent, night-time CO₂ uptake) — or a facultative combination. We only show a trait card for the noteworthy C4/CAM cases; C3 is the unremarkable majority, kept in the data but not surfaced as a card.
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
For woody plants that have a height but no measured crown, we estimate width = height × a crown-to-height ratio fit for that plant’s form (conifers narrower than broadleaf trees, shrubs widest), calibrated on our measured open-grown crowns and capped at the largest one ever measured. A measured crown always wins; herbaceous plants get nothing (no anchor).
Honest limits: A coarse class-median estimate for garden-scale spacing, not a measurement; woody single/multi-stem forms only.
McKenzie et al. assigned each species a flower colour with a GPT-4V vision model over iNaturalist photos. We use the confident tier plus a separately-labelled lower-confidence top-up (mostly inconspicuous green/brown flowers), and render it as a small tint — never as an asserted fact, and kept out of the written synopsis.
Honest limits: AI image inference (~87% expert agreement on the confident tier); a decorative, confidence-tiered indicator, not a measured trait.
Sources for this entry (36) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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