Ceratonia L. (1753), in the family Leguminosae subfamily Caesalpinioideae, contains 2 species, including C. siliqua L., the carob.

Description Trees to 10m, often wide-spreading. The leaves are alternate, evergreen, pinnate, with around 4 pairs of almost-round leaflets. The flowers are small, greenish, in elongated, catkin-like bunches, often unisexual, males and females sometimes on different trees, rarely together on the same tree or in the same bunch. Sepals 5, soon falling; petals absent. Stamens 5, with the filaments separate. Ovary superior, with 1 carpel containing several ovules; style 1. Pollination is presumed to be by bees. The fruits are legumes, leathery and dark brown when ripe, to 20cm long, with numerous oval seeds.

Key Recognition Features The pinnate, leathery leaves and the catkin-like flower spikes produced in autumn. The beans have a characteristic sweet, sickly, chocolate-like flavour.

Evolution and Relationships Related to tropical genera from eastern Asia, and to Gleditsia, with bunches of small flowers often growing directly on the trunk.

Ecology and Geography On dry, rocky hills; now found commonly in the Mediterranean region, but it may be an ancient cultivated plant from further south, possibly Oman. A second species is found in the Arabian Peninsula and Somalia.

Comment The carob is said to be the locust eaten by John the Baptist, and the husks eaten by the prodigal son. Nowadays carob pods are used as a substitute for chocolate and are common in animal feed. Carob is also said to be the the origin of the carat of jewelers, from the use of the beans for weighing. They weigh 189–205mg, closely approximating to the official carat weight of 200mg.

Photographs: Ceratonia siliqua