Ceanothus cordulatus

Whitethorn ceanothus


The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (flowering plants). Class - Magnoliopsida. Subclass - Rosidae. Order - Rhamnales. Family - Rhamnaceae (buckthorn). Genus - Ceanothus L. Species - Ceanothus cordulatus Kellogg

Ecology: Whitethorn ceanothus is a nitrogen-fixing shrub that grows best in open situations. Dry, open flats, pine forests, rocky ridges, and washes that have well-drained soils are common sites where whitethorn ceanothus is found. Areas that have been burned or logged are very favorable for populations of whitethorn ceanothus. It can also survive and thrives in the shade of coniferous timber. Whitethorn ceanothus has a narrow range of environments in which it thrives. It is most commonly found within sclerophyllous shrub communities in both conifer and hardwood forests of the coast and interior ranges of the Sierra Nevada. In addition to the previously listed habitats, whitethorn ceanothus also occurs in the understory of giant sequoia (Sequoiadendron giganteum) communities/groves because of its ability to tolerate low light levels.


Whitethorn ceanothus is a native, evergreen shrub. It has a low-lying, flat-topped growth habit, especially at higher elevations, and generally reaches heights between 0.6-1.5 m. Whitethorn ceanothus can form a continuous ground cover up to 3.7 m in diameter. The many short, rigid, intricately-branched stalks end in sharp spines. The numerous leaves are alternate and distinctly 3-ribbed from the base. They are small, elliptic to egg-shaped, and blunt at the tip. The leaf margins are entire or finely toothed. Flowers are in dense clusters borne on a panicle-like inflorescence. The fruit is a capsule that is slightly crested or horned and somewhat sticky at maturity. It is small, tipped by a threadlike 3-forked appendage, and 3-lobed.

Habit: Plant +- open, generally < 1.5 m. Stem: generally spreading; twigs rigid, thorn-like, pale gray to gray-green. Leaf: alternate, evergreen; stipules scale-like; petiole 2--8 mm; blade 9--25 mm, 6--18 mm wide, ovate to elliptic, 3-ribbed from base, adaxially dull green, glabrous to puberulent, abaxially paler, glabrous to puberulent, margin generally entire. Inflorescence: generally raceme- to panicle-like, generally sessile, 1--4 cm. Fruit: 3.5--5 mm wide, +- 3-ridged distally; horns 0.


Fire effects: Fire top-kills or kills whitethorn ceanothus, depending on severity. It is resistant to fire-induced mortality because of the deeply buried meristematic tissues...Whitethorn ceanothus is highly dependent on fire. After fire it regenerates by stump-sprouting or from seed depending on the severity of the burn. It is characterized specifically as an obligate sprouter in moderate fuel-consumption burns and a facultative seeder following high fuel-consumption fires. If there is repeated fire, whitethorn ceanothus brushfields can become semipermanent communities. Where fire is lacking, it does not establish and populations decrease, and in some cases are eliminated, in the shade of dense tree canopies. Fire, or similar heat treatment, is necessary to crack the seed coat to allow for absorption of water and subsequent germination. Fire aids in the germination of seeds but can also destroy them. High intensity or high frequency fires can be detrimental to the seed bank and can result in lower rates of germination. Many soil-stored seeds germinate after fire breaks seed dormancy; seedlings can account for more than half of the plants present in burn areas. Whitethorn ceanothus also stump-sprouts after fire. Burned areas stimulate nitrification through the perpetuation of nitrogen-fixing shrubs such as whitethorn ceanothus, accelerating the recycling of nutrients stored in living and dead plants.


Seed production - Whitethorn ceanothus is an insect-pollinated species... Ceanothus spp. are prolific seed producers. Thousands of viable seeds can be produced per hectare and remain dormant in the soil and duff layer until disturbance stimulates germination. Whitethorn ceanothus seeds are autochorus, meaning that the main mode of seed dispersal is by the plant itself. The seeds are small and tend to stay where they fall, unless they are carried off by birds, rodents, or ants. Ceanothus seeds can also be forcibly ejected from the seed pods when they ripen. Because of the large number of seeds produced by whitethorn ceanothus, substantial seed reservoirs exist in the soil and duff layer. The seeds of whitethorn ceanothus are refractory: requiring heat alone or in conjunction with other conditions such as cold stratification; whitethorn ceanothus is heavily dependent upon fire for germination.

Vegetative regeneration - Layering is common in whitethorn ceanothus at higher elevations where the weight of snow forces branches and stems down to the ground. Stump-sprouting from a lignotuber is also common after the top of the shrub is damaged.

Species Distribution


USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA.