Ceratonia, commonly known as carobs, is a small genus of flowering trees in the pea family Fabaceae (subfamily Caesalpinioideae, tribe Umtizieae), placed in the order Fabales. The genus is endemic to the Mediterranean region and the Middle East, though its best-known member, the carob tree (Ceratonia siliqua), has been widely introduced to regions with similar climates worldwide.
Carob trees are evergreen and can reach up to 15 metres tall, with broad semispherical crowns supported by thick, rough-barked trunks. The leaves are alternate, pinnate, and 10–20 cm long. Most trees are dioecious, with separate male and female individuals, though some are hermaphroditic. Flowers appear in autumn as numerous small blooms spirally arranged in catkin-like racemes borne directly on old wood and the trunk, a growth pattern known as cauliflory. Pollination occurs via both wind and insects. The fruit is an elongated, compressed legume pod, straight or curved, which takes a full year to develop and ripen. When ripe, the sweet pods fall and are dispersed by mammals.
The genus was long considered monotypic, consisting solely of C. siliqua, until a second species, Ceratonia oreothauma, was described in 1979 from populations in Oman and Somalia. An obsolete generic name was Acalis. A fossil species, †Ceratonia emarginata, is known from Miocene deposits of Switzerland and Hungary, attesting to the genus's ancient lineage — Ceratonia is believed to be an archaic remnant of a part of the legume family now generally considered extinct. The name Ceratonia derives from the Greek kéras ("horn"), in reference to the shape of the pods, and the carat unit for gemstone mass traces its name to the carob seed, historically used as a weight standard.
Etymology
The genus name Ceratonia derives from Greek κερατωνία (keratōnía, "carob-tree"), from κέρας (kéras, "horn"), referring to the tree's horn-shaped pods. The species epithet siliqua is Latin for "pod." The English common name "carob" traces via French, Arabic (خَرُّوبٌ, kharrūb), and Persian to Akkadian or Aramaic origins. The carat, the unit of mass for gemstones, ultimately derives its name from the Greek κεράτιον ("small horn"), referring to the uniform weight of carob seeds historically used as a standard in trade.
Distribution
Ceratonia is native to the Mediterranean region and the Middle East. The carob tree (C. siliqua) has been widely cultivated and naturalized throughout the western Mediterranean, including southern Portugal, Spain, Italy (Sicily, Sardinia), Malta, Croatia, Greece, Cyprus, Crete, eastern Bulgaria, Turkey, Israel, and Morocco. A second species, C. oreothauma, is restricted to Oman and Somalia. The genus has been introduced to other regions with Mediterranean-like climates globally.
Ecology
Ceratonia is a xerophytic genus well adapted to Mediterranean conditions, surviving on just 250–500 mm of rainfall per year, though 500–550 mm is needed for fruiting. The trees have deep root systems that tolerate a wide variety of soil conditions and are fairly salt-tolerant (up to 3% soil salinity). They prefer well-drained sandy loams and are intolerant of waterlogging. The genus is considered an archaic remnant of a now-extinct part of the legume family. It remains unclear whether carob trees establish symbiotic root nodules with rhizobia to fix atmospheric nitrogen — studies have produced conflicting results. A fossil species, †C. emarginata, is known from Miocene deposits in Switzerland and Hungary.
Cultivation
Carob trees are propagated primarily from seed, sown in nurseries in early spring and transplanted after the last frost. Vegetative propagation is naturally limited by low rooting potential; grafting and air-layering are more effective alternatives. Trees begin cropping 3–4 years after budding in favorable conditions but may take up to 8 years on marginal soils, reaching full bearing at 20–25 years. Traditional orchards are planted at low densities of 25–45 trees per hectare, with male or hermaphroditic trees serving as pollenizers. Management is minimal — light pruning, occasional tilling for weed control, and supplemental nitrogen fertilization. Although drought-adapted, two or three summers of irrigation greatly aid establishment and increase yield.
Cultural Uses
Carob pods are processed into a powder or chips used as a caffeine-free chocolate substitute. The seeds yield locust bean gum (carob gum), a widely used food thickening agent. Spain is the world's largest carob producer, followed by Italy and Morocco. The tree is also grown as an ornamental in gardens and landscapes.
History
The genus Ceratonia was long considered monotypic, containing only the carob tree (C. siliqua). This changed in 1979 when a second species, Ceratonia oreothauma, was identified from Oman and Somalia. A fossil species, †Ceratonia emarginata, is known from Miocene deposits, indicating the genus has existed for millions of years. An obsolete name for the genus is Acalis.
Taxonomy
Ceratonia belongs to the family Fabaceae, subfamily Caesalpinioideae, and tribe Umtizieae, within the order Fabales. An obsolete generic name is Acalis. The genus contains two extant species: C. siliqua (widespread Mediterranean) and C. oreothauma (Oman, Somalia), plus the fossil species †C. emarginata. It is considered an archaic remnant of a now-extinct lineage within the Fabaceae.
