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Weed Alert!

Ceratonia siliqua L.
(carob tree, locust bean tree, St. John's bread)

Summary: new plant of unknown characters
Ceratonia siliqua is commonly cultivated in California and is native to the Mediterranean and Middle East. Spanish missionaries first introduced the carob tree into Mexico and southern California. In 1856, seedlings were distributed from Spain to the southern states of the US. In 1859, more seeds were brought from Israel. Many carobs were planted as ornamentals and street trees during this time in Texas, Arizona, California, and in Florida (2). The trees are also used for erosion control and the pods for stock feed, human consumption, commercial thickeners, pet foods, cosmetics, and pharmaceuticals (4).

C. siliqua has recently been reported escaping from cultivation in California (3). C. siliqua rarely invades undisturbed habitats but escapes easily along washes and other moist areas. This species has escaped in Los Angeles Co., the San Jose Hills in Pomona, in San Bernardino Co., and is one of the worst weeds on the University of California, Riverside Botanic Gardens (3).

(Click on thumbnail images for a closer view)


Young fruit



Ceratonia siliqua L. (Fabaceae -- the bean family) is a slow growing evergreen tree. C. siliqua attains a height of 15-17 m and can have a trunk 85 cm in diameter by the time it is 18 years old. The leaves are pinnate with 6-10 opposite leaflets. The leaflets are oval and rounded at the apex, 2.5-6.25 cm long, dark green and leathery. The red flowers are small and borne in clusters. Flowers bloom from September to November on older wood in the Mediterranean. Separate trees are male, female or hermaphroditic. The fruit is light to dark brown,10-30 cm long and 1-2.5 cm wide. Fruit shape is oblong, flattened, straight or slightly curved and with a thickened margin. Ripening late in the summer, during bloom, the fruit is shiny, tough and fibrous. The fruit contains a soft, pale brown pulp and 5-15 flattened, hard seeds. When the pod is fully ripe and dry, the loose seeds rattle. The ripe fruit can be eaten (avoid the seeds) but has an odor similar to Limburger cheese (2).

Scientific and Common Names:
The common names for Ceratonia siliqua--locust bean tree and St. John's bread--were derived from the Bible. St. John the Baptist is said to have sustained himself on fruits of the "locust" tree when wandering in the wilderness. The word locust is also used for other trees with pinnate leaves and oblong pods such as North American natives Gleditsia and Robinia (2).

The impacts of this new invader are unknown. However, Ceratonia siliqua has the following characteristics:
1)resprouts when cut (3);
2)adaptable to different soil types (rocky, sandy, heavy loam) (2);
3)has no serious disease problems (2);
4)is extremely drought-tolerant (2);
5)common in cultivation, which increases the chance of escape into wildland areas.

Native Range:
Ceratonia siliqua is native to the Mediterranean and Middle East (4).

Range As An Invader:
Ceratonia siliqua grows best in Mediterranean-type climates with cool winters, mild springs, and hot summers with little to no rain (USDA zones 9-10). This tree is extremely drought tolerant and readily withstands temperatures up to 122 F (50 C). C. siliqua is hardy when mature to 20 F (-6.7 C) (2). Young trees or shoots and flowers of mature trees are susceptible to frost damage at temperatures at or below 25 F (-3.9 C). The tree grows well on rocky hillsides, deep sands, or heavy loam, but is not tolerant of acid or wet soils (2).

Reproduction and Methods of Dispersal:
Coyotes frequently consume carob fruits and disperse the seeds in their scat (3). In urban areas, carob seeds in mulch made from C. siliqua street trees readily germinates (3). In Israel, the fruits are fed upon by fruit bats that eject (spit out) the seeds in pellets, which disperses them away from the tree. Ejected seeds germinate as readily as the seeds taken directly from the fruit (1).

1. In the UC Riverside Botanic garden, the trees were cut to the ground. They resprouted but were cut again before they were sufficiently mature to flower (3).
2. Growth of seedlings and resprouting trunks may be limited by jackrabbits that feed on the foliage (3).

1. Izhaki, I., Korine. C., and Arad, Z. 1995. The effect of bat (Rousettus aegyptiacus) dispersal on seed germination in eastern Mediterranean habitats, Oecologia 101:335-342.
2. Morton, J.F. 1987. Carob In: Fruits of Warm Climates, CF Dowling, Jr. (ed.) Miami, Fl. pp.121-124.
3. Sanders, A.C. 1996. Noteworthy Collections: California, Madrono 43(4):526.
4. Tous, J. and Ferguson, L. 1996. Mediterranean fruits In: Progress in New Crops, J. Janick (ed.) ASHS Press, Arlington, VA. pp. 424-425.

--Tunyalee Martin/Wildland Invasive Species Team; April 2001

Updated January 2005
©The Nature Conservancy, 2001