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Trees, shrubs or lianas, very rarely herbs ( Neptunia and Mimosa p.p.); branches unarmed or armed with stipular thorns (rarely axillary thorns) or scattered prickles on the internodes. Stipules rarely absent, usually caducous. Leaves alternate, usually bipinnate (unipinnate in Inga, transformed into phyllodes in Acacia subg. Phyllodineae), usually provided with extrafloral nectaries on rachis and pinnae. Inflorescences bracteate, simple or compound, racemose; inflorescence units usually consisting of pedunculate glomerules, spikes or spike-like racemes, which are aggregated into axillary or terminal panicles. Pedicels usually short or absent. Flowers actinomorphic, bisexual, unisexual, or rarely neuter, usually small and white, greenish or yellow. Disk, when present, intrastaminal. Stamens few to numerous, free or united into a tube, the latter sometimes united with the corolla-tube at the base. Anthers dorsifixed, ± quadrangular in outline, sometimes with a small, caducous gland at the apex. Ovary(-ies) solitary (to several and free), superior, 1-celled; style filiform; stigma small, tubular(-infundibular), terminal. Ovules anatropous, parietal. Fruit a pod, dehiscent or indehiscent, sometimes breaking into 1-seeded segments. Seeds usually in two rows from the single placenta, inserted transversely, obliquely or longitudinally, mostly ovate-orbicular in outline, often compressed; funicle rarely developed into an aril ( Acacia p.p., Pithecellobium); the testa osseous, coriaceous or chartaceous usually with a ± peripheral furrow, the pleurogram. Distribution — About 60 genera and some 3000 species, mainly in the tropics and the subtropics, but some genera (e.g. Acacia and Albizia) extending into the warm-temperate zone; in Malesia: 19 genera, of which 15 native, with 1 endemic, viz. Wallaceodendron in N Celebes and the Philippines. Among the remaining 14 native genera, 5 are pantropical (Acacia, Albizia, Entada, Neptunia, Parkia), 3 are shared with continental S Asia and tropical N Australia ( Adenanthera, Archidendron, Cathormion), 2 with Melanesia and the west Pacific (Schleinitzia, Serianthes), 2 with Australia ( Pararchidendron, Paraserianthes), 1 with New Caledonia, the Solomon Islands and Australia (Archidendropsis), and 1 with India and tropical Africa/Madagascar (Dichrostachys). The total number of native and naturalized species is c. 150. Furthermore, an enumeration of c. 45 cultivated species is given at the end of this revision (p. 205). In both Keys to the genera 7 commonly cultivated genera are included.
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