Senegalia

Shrubs or trees [lianas], armed, rarely unarmed. Stems usually erect [spreading or climbing], pubescent or glabrous; twigs terete to angulate, usually straight, short shoots present or absent. Leaves alternate, even-bipinnate; stipules present, caducous, herbaceous; petiolate, petiole channeled, gland present [absent] in channel; pinnae 1–30(–43) pairs, mostly opposite; leaflets 3–55 pairs per pinna, opposite, sessile or subsessile, blade margins entire, surfaces glabrous or pubescent. Inflorescences 6–250+-flowered, terminal or axillary, heads or spikes, usually in pseudoracemes or pseudopanicles; bracts present. Flowers mimosoid; calyx campanulate, lobes 5; corolla white, creamy white, or yellow, lobes 5; stamens 40–160, distinct, exserted, creamy or yellow, fading reddish brown; anthers dorsifixed, dehiscing longitudinally, sometimes with a small stalked gland; ovary stipitate or sessile with nectiferous disc at base, usually pubescent; style and stigma filiform. Fruits legumes, stipitate or sessile, mostly flattened, straight to falcate, oblong [linear], usually dehiscent along sutures, glabrous or pubescent. Seeds 3–16[–25], uniseriate, sometimes flattened, ovoid to ellipsoid, not surrounded by pulp; pleurogram usually U-shaped. x = 13.

Distribution

sw, sc United States, Mexico, West Indies, Central America, South America, Asia, Africa, Pacific Islands, Australia, nearly worldwide in tropical to warm temperate areas.

Discussion

Species ca. 235 (6, including 2 hybrids, in the flora).

Senegalia is separated from related genera by the presence of prickles, the absence of stipular spines, a nectiferous disk at the base of the stipitate ovary, and portate pollen. Based on mor­phological evidence, L. Pedley (1978, 1986) separated Senegalia from other members of Acacia in the broad sense. The separation was further supported by phylogenetic analysis of chloroplast matK and trnl sequence datasets, in which species of Senegalia formed a monophyletic clade (D. S. Seigler et al. 2006b).

Selected References

None.

Lower Taxa

Senegalia berlandieri, Senegalia greggii, Senegalia roemeriana, Senegalia wrightii, Senegalia ×emoryana, Senegalia ×turneri

Key

1	Leaflets 25–55 pairs per pinna.	Senegalia berlandieri
1	Leaflets 3–21 pairs per pinna.	> 2
2	Inflorescences cylindric spikes, lengths 3+ times widths.	> 3
3	Leaflet blades usually 2.8–5.5 mm; flowers sessile or short-pedicellate, pedicels.	undefined
null	6 mm.	Senegalia greggii
3	Leaflet blades usually 5.5–9.2 mm; flowers pedicellate, pedicels 0.5–2.1 mm.	Senegalia wrightii
2	Inflorescences globose or subglobose heads, lengths less than 2 times widths.	> 4
4	Leaflets 3–10 pairs per pinna, blades usually obovate, rarely oblong.	Senegalia roemeriana
4	Leaflets 13–21 pairs per pinna, blades oblong.	> 5
5	Mature leaflet blades mostly less than 5.4 mm (3–7 mm).	Senegalia × emoryana
5	Mature leaflet blades mostly more than 5.4 mm (5.1–9.3 mm).	Senegalia × turneri