Caesalpinia L. (1753), in the family Leguminosae subfamily Caesalpinioideae, contains around 150 species in the tropics of America, Asia, and Africa, with a few species extending into temperate areas.

Description Trees to 10m, or more in tropical species, shrubs, or climbers, often with thorns. The leaves are alternate, evergreen or deciduous, usually 2-pinnate. The flowers are in elongated bunches, usually yellow. Sepals 5, unequal, joined at the base to form a tubular calyx; petals 5, more or less equal, the upper often the smallest. Stamens 10, often much longer than the petals, the filaments often hairy at the base. Ovary superior, with 1 carpel containing several ovules; style 1, very short. Pollination is by bees and butterflies, and by hummingbirds in C. gilliesii (Hook.) D. Dietr. and C. pulcherrima (L.) Sw., which have very long stamens. The fruits are flattened, often woody or prickly legumes with 1 or more seeds.

Key Recognition Features The ferny, 2-pinnate leaves and the flowers with almost equal petals, the lowest sepal partially or completely enclosing the others.

Evolution and Relationships Around 180 genera belong to the subfamily Caesalpinioideae, including the commonly planted tropical trees Delonix regia (Bojer) Raf., which has bright red flowers and is called the flamboyant, and Bauhinia L., with white or pink, orchid-like flowers and characteristic leaves that have 1 leaflet with 2 rounded lobes. The Caesalpinioideae has the least specialised flowers of the 3 subfamilies of Leguminosae, and DNA studies suggest that some genera included in it are more closely related to the other traditional subfamilies than they are to each other.

Ecology and Geography In open woods and scrub and on rocky hillsides in South America and South East Asia. The almost hardy climber C. decapetala (Roth) Alston var. japonica (Sieb. & Zucc.) Isley is found in China and Japan.

Comment A diverse genus, with many species planted throughout the tropics.