Shrubs or trees, armed. Stems erect to spreading, glabrous or pubescent; twigs terete [angulate], some flexuous, short shoots usually present. Leaves alternate, even-bipinnate, usually clustered on short shoots, leaves of short shoots usually smaller, with fewer pinna pairs and leaflets than alternately arranged leaves on faster growing branches; stipules present, spinose, paired at nodes, [asymmetric], straight to curved, woody, in some species enlarged and inhabited by ants; petiolate, petiole channeled, glabrous or pubescent, petiolar gland 1–30; pinnae 1–45[–60] pairs, mostly opposite; leaflets 2–47 pairs per pinna, usually opposite, sessile or subsessile, blade margins entire, surfaces glabrous or pubescent. Inflorescences 50–180(–1500+)-flowered, primarily axillary, globose heads or cylindrical spikes, solitary or clustered in leaf axis or on short shoots, sometimes pseudoracemes; bracts present. Flowers mimosoid; calyx campanulate, lobes 4 or 5; corolla yellow, white, or cream, lobes 4 or 5; stamens 15–120, distinct, exserted, yellow or white, [gold or creamy white]; anthers dorsifixed, eglandular; ovary sessile or short-stipitate, usually glabrous; style and stigma filiform. Fruits legumes, stipitate, flattened to terete, straight to falcate, linear to oblong, usually dehiscing along both sutures, sometimes indehiscent, glabrous or pubescent. Seeds 6–10(–20), uniseriate or biseriate, sometimes flattened, ovoid to ellipsoid, sometimes surrounded by pulp; pleurogram U-shaped. x = 13.

Distribution

s, sw United States, Mexico, West Indies, Central America, South America, Europe, Asia, Africa, Australia, introduced nearly worldwide in tropical to warm temperate regions.

Discussion

Species ca. 160 (10 in the flora).

There is considerable evidence that Acacia in the broad sense is not a natural or monophyletic group. Largely because the segregation of Acacia in the broad sense into at least five genera would result in requiring a change in generic epithet for about 1000 Australian species of subg. Phyllodineae (de Candolle) Seringe, at the 17th International Botanical Congress in 2005, the type of Acacia was changed from A. scorpioides (Linnaeus) W. F. Wright to the Australian species A. penninervis (B. R. Maslin 2008; J. McNeill and N. J. Turland 2010). As a result of this change, plants of former Acacia subg. Acacia should be placed in Vachellia (Maslin et al. 2003; D. S. Seigler and J. E. Ebinger 2005).

Selected References

None.

Lower Taxa

Vachellia bravoensis, Vachellia choriophylla, Vachellia constricta, Vachellia cornigera, Vachellia farnesiana, Vachellia macracantha, Vachellia rigidula, Vachellia schottii, Vachellia tortuosa, Vachellia vernicosa

Key

1	Inflorescences cylindrical spikes.	> 2
2	Stipular spines enlarged, 4–10 mm wide near base; pinnae 3–14 pairs.	Vachellia cornigera
2	Stipular spines 0.6–2.1 mm wide near base; pinnae 1 pair.	Vachellia rigidula
1	Inflorescences globose heads.	> 3
3	Leaflet blades 16–28 mm.	Vachellia choriophylla
3	Leaflet blades 1.1–6.3 mm.	> 4
4	Involucral bracts near middle of peduncles.	> 5
5	Leaflet blades linear and subterete.	Vachellia schottii
5	Leaflet blades elliptic, oblong, or oval and flat.	> 6
6	Stems not glutinous; pinnae 2–8 pairs.	Vachellia constricta
6	Stems glutinous; pinnae 1 or 2(or 3) pairs.	Vachellia vernicosa
4	Involucral bracts at base of heads.	> 7
7	Pinnae 12–45 pairs.	Vachellia macracantha
7	Pinnae 1–8 pairs.	> 8
8	Petiolar glands donut-shaped, at or just below lowermost pinnae.	Vachellia bravoensis
8	Petiolar glands circular to slightly elongated, not donut-shaped, usually medial on petiole.	> 9
9	Legumes nearly terete in cross section, not constricted between seeds; seeds biseriate or irregularly arranged.	Vachellia farnesiana
9	Legumes narrowly elliptic in cross section, constricted between seeds; seeds uniseriate.	> 10
10	Stems usually slightly flexuous; petioles 6–12(–17) mm.	Vachellia farnesiana
10	Stems strongly flexuous; petioles 3–7 mm.	Vachellia tortuosa