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Name

Acacia nilotica (Linnaeus) Willdenow ex

Formal description

Shrub or small tree to 14 m tall.  Bark dark gray to dark brown to black, furrowed.  Twigs dark reddish brown to dark gray, slightly flexuous, lightly to densely pubescent.  Short shoots commonly absent.  Leaves alternate, sometimes a few clustered together at a node, 15-100 mm long.  Stipular spines light to dark gray, symmetrical, terete, straight, stout, to 50(150) x 2.5 mm near the base, lightly to densely pubescent.  Petiole adaxially grooved, 4-40 mm long, lightly to densely pubescent; petiolar gland solitary, usually located between or just below the lower pinna pair, sessile, circular to slightly elongated, 0.2-1.2 mm long, apex depressed, glabrous, sometimes absent.  Rachis adaxially grooved, 0-80 mm long, usually pubescent, a sessile, circular gland, 0.2-1.0 mm across between some or all of the pinna pairs.  Pinnae 1 to 9 pairs per leaf, 18-40 mm long, 4-18 mm between pinna pairs.  Petiolules 1.0-1.8 mm long.  Leaflets 11 to 27 pairs per pinna, opposite, 0.8-2.1 mm between leaflets, oblong, 2.5-6.5 x 0.8-1.7 mm, mostly glabrous, lateral veins not obvious, only one vein from the base, base obtuse and oblique, margins lightly ciliate, apex obtuse.  Inflorescence a densely flowered globose head, 8-12 mm across, solitary or in clusters of 2 to 10 at the nodes.  Peduncles 12-40 x 0.4-0.8 mm, usually densely puberulent.  Involucre 4- to 5- lobed, usually located near the middle of the peduncle, puberulent, persistent.  Floral bracts spatulate, 1.2-1.6 mm long, puberulent, deciduous.  Flowers sessile, bright yellow; calyx 5-lobed, 1.0-1.8 mm long, glabrous or nearly so; corolla 5-lobed, 2.0-3.2 mm long, glabrous or nearly so; stamen filaments 3.5-6.0 mm long; ovary glabrous, on a stipe to 0.2 mm long.  Legumes dark brown to black, straight to slightly curved, flattened, usually constricted between the seeds, oblong, 40-200 x 9-21 mm, coriaceous, not reticulately striate, densely white tomentose, eglandular, indehiscent; stipe to 15 mm long; apex acuminate beaked.  Seeds uniseriate, no pulp, light to dark brown, ovoid to slightly ellipsoid, flattened, 6.5-10.4 x 6.0-9.0 mm, smooth; pleurogram nearly oval, 4-7 mm across. Flower in July to September. Chromosome number:  Not determined.

Distribution

Widespread in tropical and subtropical Africa and Asia, extending as far east as India.  Adventive in the New World where it is sometimes planted and occasionally escaped into disturbed habitats.

Additional info

Acacia nilotica is an exceedingly variable species, nine subspecies having been delimited, mainly on differences in the shape, size and pubescence of the fruits (Ross 1979). Closely related to members of the Acacia farnesiana group of the New World, it has stipular spines to 150 mm long, petioles to 30 mm long often with a large, petiolar gland near the lower pinna pair, leaves with 1-9 pinnae pairs, 11-27 pairs of leaflets per pinna, and a capitate inflorescence. Acacia nilotica differs from all native South American species by having the involucral bracts near the middle of the peduncle, flattened legumes that are relatively wide (9-21 mm), densely white tomentose and usually deeply constricted between the seeds. The description presented here is based largely on the New World specimens examined.

Flowering time

July to September.

Representative specimens

ANGUILLA:

ANTIGUA:

BAHAMAS:

Exuma:

BARBADOS:

CUBA:

GRENADA:

GRENADINES:

GUADELOUPE:

JAMAICA:

MARTINIQUE:

MONTSERRAT:

ST. LUCIA:

ST. VINCENT:

TOBAGO:

VIRGIN ISLANDS (US):

UNITED STATES:

Florida:

Dade Co.:

COLOMBIA:

Antioquia:

ECUADOR:

Guayas:

Santa Cruz:

GUYANA:

Guyana:

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