Fabaceae (Leguminosae)

Salient features: Trees, shrubs or herbs, leaves usually pinnate compound with pulvinate base, flowers actinomorphic, corolla not papilionaceous, petals valvate, sepals united, odd sepal anterior, stamens 4-many, free or connate, filaments often long exserted and showy, ovary superior, carpel 1, fruit a pod or lomentum.

Major genera: Acacia (1300 species), Mimosa (500), Inga (250), Pithecellobium (170), Calliandra (150) and Albizia (150).

Description: Trees (Acacia, Albizia), shrubs (Calliandra) or herbs (Mimosa pudica), rarely climbers (Entada), or aquatic plants (Neptunia). Leaves alternate, pinnately or palmately compound, sometimes simple, leaf base (sometimes also the base of leaflets) pulvinate, petiole sometimes modified into phyllode (Acacia auriculiformis), stipules present, sometimes spiny and hollow inside sheltering ants (Acacia sphaerocephala), leaves of Mimosa pudica sensitive to touch and showing sleeping movements. Inflorescence racemose, in racemes (Adenanthera) or spikes (Prosopis), sometimes in cymose heads (Mimosa, Acacia). Flowers small, bracteate (bracts usually caducous), sessile, or short-pedicelled, bisexual, actinomorphic, perigynous. Calyx with 5 sepals (4 in Mimosa), connate, odd sepal anterior, usually valvate, teeth small. Corolla with 5 petals (4 in Mimosa), free or united (Acacia, Albizia), valvate. Androecium with 4-many (4 in Mimosa, 10 in Prosopis, numerous in Acacia and Albizia) stamens, free (Acacia, Prosopis) or filaments connate (Albizia), anthers bithecous, dehiscence longitudinal, filaments long and anthers usually exserted. Gynoecium with a single carpel, unilocular with many ovules, placentation marginal, ovary superior, style single, curved. Fruit a legume or lomentum (Mimosa, Acacia); seeds 1-many, seed coat hard, endosperm minute or absent.
Economic importance: The subfamily is of lesser economic importance. Sensitive plant touch-me-not (Mimosa pudica) is grown as a curiosity. Various species of Acacia (A. senegal, A. stenocarpa) yield gum arabic. The pods and seeds of mesquite (Prosopis juliflora) are used as animal feed, wood in cooking meats. Wood of Xylia is hard and used in ship building. Calliandra, Dichrostachys are grown as ornamentals, Pithecellobium as a useful hedge plant.

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