Vachellia Wight & Arn.
Genus composed of about 160 species previously included in the genus Acacia. It is distributed across Asia, Australia, America and Africa, with more than 70 species in the latter. It includes species of trees and shrubs, with flowers grouped into globose glomeruli, and bipinnate leaves with spiny stipules, often swollen at the base. The most diagnostic characters for the genus are mainly concerned with the leaves (number of pinnae and leaflets), the size of the stipular spines and the properties of the pods. Regarding the flowers, they are very simple and of little diagnostic value, arranged in spherical inflorescences, and have a small calyx, gamosepalous, campanulate with 5 teeth, and a corolla, also small with 5 petals fused at the base, oblong or ovate, glabrous or hairy. The flowers have numerous stamens with filaments long, white, cream, whitish-yellow, yellow or yellowish-orange, which give the colour to the inflorescence.
In addition to the native species, V. farnesiana and V. karroo appear punctually naturalised in North Africa. V. farnesiana (L.) Wight & Arn., (Mimosa farnesiana L., Acacia farnesiana (L.) Willd.) is a deciduous shrub or tree native to tropical America, now cultivated in most of North Africa. It has pinnate leaves, with 2-8 pinnae, each with 10-21 pairs of leaflets 2-7 × 0.75-1 mm, and small stipular spines, 0.5-1.5(3) cm; flowers, yellow, arranged in spherical capitula 1-1.5 cm in diameter, and pods 4-7.5(9) × 0.8-1.5(2) cm, hard and subcylindrical in cross section. A very similar species is V. karroo (Hayne) Banfi & Galasso (A. karroo Hayne, A. horrida auct.), native to southern Africa and cultivated across most of the territory, it is differentiated by its leaves, with more pinnae [(1)2-7(13) pairs] and leaflets [5-15(27) pairs by pinna, 1-3(5.5) mm wide], larger spines 0.5-10(25) mm, and pods (4)6-16(21) × 0.6-1 cm., compressed and torulose.
Brenam, J.P.M. 1983. Manual on taxonomy of Acacia species. Present Taxonomy of Four Species of Acacia (A. Albida, A. Senegal, A. Nilotica, A. Tortilis). FAO. Roma. 47 pp. http://www.fao.org/docrep/006/Q2934E/Q2934E00.htm#TOC
Celle, J. & Manière, R. 1980. Remarques sur la distribution en Afrique nord-occidentale d’Acacia seyal Delile et d’Acacia ehrenbergiana Hayne. Candollea 35: 183-200.
Chevalier, A. 1928. Révision des Acacia du nord, de l’ouest et du centre africain. Revue de botanique appliquée et d’agriculture coloniale 77: 46-52; 78: 123-130; 79: 197-206; 80: 263-270; 81: 357-362; 82: 432-434; 83: 496-501; 84: 574-579; 85: 643-650; 86: 707-715.
Kyalangalilwa, B., Boatwhright, J.S., Daru, B.H. Maurin, O. & Van Der Bank, M. 2013. Phylogenetic position and revised classification of Acacia s.l. (Fabaceae: Mimosoideae) in Africa, including new combinations in Vachellia and Senegalia. Bot. J. Linn. Soc. 172: 500-523.
Miller, J.T. & Seigler, D. 2012. Evolutionary and taxonomic relationships of Acacia s.l. (Leguminosae: Mimosoideae). Austr. Syst. Bot. 25: 217-224.
Ross, J.H. 1981. An analysis of the African Acacia species: their distribution, possible origins and relationships. Bothalia 13 (3/4): 389-413.
Key to species
1 Inflorescences white, cream or whitish-yellow 2
1 Inflorescences yellow, golden-yellow or yellow-orange 5
2 Pod not torulose, with winged margin, wing 1.5-2.5 mm Vachellia oerfota
2 Pod ± torulose, wingless margin 3
3 Pod in a spiral when ripe Vachellia tortilis
3 Pod straight or falcate, not in a spiral 4
4 Pod straight, (7)15-22 mm wide, glabrous or puberulous towards the base Vachellia etbaica
4 Pod falcate, 6-12 mm wide, puberulent-tomentose Vachellia gerrardii
5 Leaves with 1-3(4) pairs of pinnae; pinnae with 5-12 pairs of leaflets; shrub or small tree, up to 4 m 6
5 Leaves —or at least some of them— with 3-17 pairs of pinnae; pinnae with (8)10-27(30) pairs of leaflets; tree up to 20 m 7
6 Spines 1-2.5 cm; pod 8-20 cm × 8-15 mm, with 6-15 seeds10-13 mm long Vachellia gummifera
6 Spines (2)4-6(7) cm; pod (3)4-10(12) cm × 4.5 mm, with 6-8 seeds 4-6.5 mm long Vachellia flava
7 Pod 5-10 mm wide, very slightly compressed between the seeds, dehiscent Vachellia seyal
7 Pod 15-22 mm wide, sharply torulose, indehiscent, disarticulating into segments Vachellia nilotica
Updated by: J.A. Devesa & M. de la Estrella.