Acacia nilotica (L.)Delile

Code

ACANL

Growth form

Tree

Biological cycle

Perennial

Habitat

Marshland

 Global description

Acacia nilotica is a small tree 4 to 10 m tall. Young stems pubescent and whitish, darker when old. Leaves alternate, compound, bipinnate, with 3 to 10 pairs of opposite pinnae, 2 to 3 cm long, each with 10 to 20 pairs of oblong leaflets, 5 to 8 mm long and 1.5 mm wide with apex obtuse. Presence of a gland under the base of the first pair of pinnae. A pair of strait and white thorns (spiny stipules) at the base of each leaf 0.6 to 5 cm long. Inflorescences in yellow head, long pedunculate, with 2 small bracteoles in the middle of the peduncle. The fruit is a linear, slightly curved, flattened pod of a slightly hairy greenish-gray color measuring 10 to 15 cm long and 1 cm wide. It is heavily strangled between each seed.

New Caledonia: The average dormancy period is 2 years, beyond which the seed is no longer viable. The ingestion of the pods by the cattle promotes the germination of the seeds after 6 days in the digestive transit which leads to the successive infestation of the plots. Germination occurs with heavy rains of the warm season. Young seedlings grow rapidly in overgrazed areas, along creeks and flooded areas. Flowering occurs after 3 years, in cool season and in dry season. The pods mature from November.

Acacia nilotica is a small tree with a lifespan of 30 to 60 years that reproduces by seeds (175 000 viable seeds per year), dispersed by water runoff, mud, livestock and humans.

 

Acacia farnesiana can be distinguised from Acacia nilotica by spines and pod shape.

Spines	Pod	Species
Strait, short (2 (-3) cm) and brown	Subcylindrical, 4-10 cm, dark colored	Acacia farnesiana
Strait, long (0,5 - 10 cm) and white	Tightly oblong, compressed between seeds, tomentose, and white-grey	Acacia nilotica

 

Acacia nilotica grows in areas with arid climates, but at the edge of a stream or pond, in marshlands or temporarily flooded environments, on heavy clay or sandy-loam soils.

Mauritius: Naturalised in the Yemen vallee and in the Tamarin area.
Reunion: Absent

Origin

Acacia nilotica is native to the arid and semi-arid zones of Africa and East Asia

Worldwide distribution

This Acacia is found throughout East Africa, as far as India. Introduced and naturalized in Mauritius and Rodrigues, in the north of Australia. and in Oceania.

Overall harmfulness

Acacia nilotica is one of the 300 major invasive species of tropical Australia (7 million ha invaded) and Oceania including New Caledonia (limited to the region of Karikaté, Tontouta). Acacia nilotica thickets at the edge of a pond or stream prevent livestock from accessing the water.

Local harmfulness

New Caledonia: Young shrubs form impenetrable dense spiny thickets that are very troublesome for handling livestock with horses, vehicle tires and access to watering points. Adult individuals compete with forage plants for water and light.

 Local control

New Caledonia: Contamination of uninvaded pastures should be prevented by controlling movement of livestock, avoiding areas with mature pods. Herds from infested areas may stay in a quarantine plot. The use of sheep allows the seeds to be destroyed by chewing. To limit the spread, stands must eliminate along the rivers by pulling down the adults with heavy equipment or by chemical treatment (triclopyr) when the leaves are present (brushing the cut stumps, on cut bark, injection around the trunk every 8 cm). On young stands, spraying (repeated once) is carried out on 2-month-old resprouts after gyrogrinding (fluroxypyr or tryclopyr + picloram).

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Acacia%2520nilotica