Changes

:Chromosome number: 2''n'' = 26

== Vernacular names ==

Promelacacinidins and a variety of tetrahydroxyflavonoids have been isolated from the heartwood.

Medium-sized deciduous tree up to 20(–30) m tall; bole usually straight, up to 75(–90) cm in diameter, usually beset with prickles on large knobs, but these often absent in old trees; bark rough, fissured, dark brown to blackish; slash pale to deep pink or red; crown conical in young trees and rounded in mature trees; branchlets usually glabrous, with pairs of hooked, blackish prickles up to 7 mm long just below the nodes. Leaves alternate, bipinnately compound, with 2–4 pairs of pinnae; stipules small, caducous; petiole with or without gland, rachis sometimes with gland between top 1–2 pairs of pinnae; leaflets in 1–2 pairs per pinna, obliquely obovate-orbicular to obovate-elliptical, (7–)10–35(–50) mm × 7–30(–50) mm, apex rounded to emarginate, usually glabrous. Inflorescence an axillary spike 1–10(–12) cm long, often in fascicles at the base of young shoots; peduncle 0.5–2.5 cm long. Flowers bisexual, regular, 5-merous, small, creamy white but reddish brown in bud, fragrant, sessile; calyx cup-shaped, 1.5–2 mm long; corolla 2–2.5 mm long, with short lobes; stamens numerous, free, 3.5–6 mm long; ovary superior, very shortly stalked, style slender. Fruit an oblong pod 6–18 cm × 1.5–2.5 cm, straight, glabrous, dark brown, longitudinally dehiscent, 3–7-seeded. Seeds flattened orbicular to lens-shaped, 12–13 mm in diameter.

''Acacia'' is a large pantropical genus, comprising more than 1300 species; most of them distributed in Australia (more than 900), more than 200 in America, and about 130 in Africa. ''Acacia nigrescens'' belongs to subgenus ''Aculeiferum'', which comprises all African ''Acacia'' species with non-spinescent stipules and hooked prickles. ''Acacia nigrescens'' is characterized by prickles on large knobs on the trunk and the large and few leaflets.

Growth is slow, with maximum annual increment of 60 cm in height, usually much less. ''Acacia nigrescens'' is completely deciduous and bare for several months. It frequently flowers when leafless. The flowers are an important food resource to giraffe in the late dry season, and it has been suggested that giraffe could be a pollen vector. Nodulation and nitrogen fixation have been confirmed.

== Ecology ==

''Acacia nigrescens'' occurs in woodland and bushland, commonly near rivers, up to 1200(–1600) m altitude. It usually grows on shallow soils on rocky hillsides and on alluvial soils in the valleys. It is often common and locally dominant on loamy soils. The tree is resistant to fire.

== Management ==

''Acacia nigrescens'' has proven easy to produce in the nursery. The seeds are usually sown into seedbeds, but sowing directly into pots is also possible because of a high germination rate. Seedlings suitable for transplanting have been produced in less than 9 months.

== Genetic resources ==

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