Trees or shrubs, usually armed, rarely unarmed; taprooted, forming underground spreading horizontal runners. Branches ascending or spreading. Stems glabrous or pubescent. Leaves alternate, even-bipinnate; stipules present, inconspicuous and early deciduous or modified spines; petiolate, petiole with sessile, circular glands; pinnae 1 or 2(or 3)[–7] pair(s), opposite, apex with scalelike mucro or spine; leaflets 6–60, alternate or opposite, overlapping or not, blade margins entire, surfaces sometimes glaucous, glabrous or pubescent. Inflorescences 40–100+-flowered, axillary, spikes or heads [racemes]; bracts absent. Flowers mimosoid; calyx campanulate, lobes 5, connate proximally, sometimes striate; corolla yellow, cream-yellow, purple-brown, greenish white, or yellow-green, [reddish], petals connate or distinct, linear; stamens 10 (5 + 5), distinct; anthers dorsifixed, introrse, elliptic, apex pedicellate with a deciduous, capitate gland. Fruits loments, stipitate or sessile, straight or spirally coiled, torulose, linear or cylindric, thickened, indehiscent, pubescent, glabrescent, or glabrous. Seeds (4 or)5–25+, gray-green, tan, yellow-tan, yellow-brown, or brown, ovoid, reniform-ovoid, ellipsoid, or oblong. x = 14.

Distribution

sw, sc United States, Mexico, South America (Argentina, Bolivia, Chile, Peru), sw Asia, Africa, deserts, dry subtropical regions, introduced in Australia.

Discussion

Species ca. 48 (6 in the flora).

Prosopis was treated by G. Bentham (1842, 1846, 1875) as polymorphic and divided into several sections based on fruit types and derivation of the spines. G. Engelmann and A. Gray (1845), as well as N. L. Britton and J. N. Rose (1928), divided the North American species into two and three genera respectively. A. Burkart (1976) adopted the position of Bentham, and most North American authors have continued to follow his treatment.

In arid countries, species of Prosopis are valued for shade, fuel, food, and forage. Due to their hardiness and abundance, they are often an important component of the vegetation in these regions. Some species are invasive and are a problem for ranchers and farmers. At least 27 species are listed as potentially noxious weeds in the United States.

Selected References

None.

Lower Taxa

Prosopis glandulosa, Prosopis laevigata, Prosopis pubescens, Prosopis reptans, Prosopis strombulifera, Prosopis velutina

Key

1	Inflorescences globose heads; loments coiled.	> 2
2	Spines 4–9 cm; leaflets touching or overlapping.	Prosopis reptans
2	Spines 0.1–2 cm; leaflets 3.5–5 mm apart.	Prosopis strombulifera
1	Inflorescences amentlike spikes; loments straight or coiled.	> 3
3	Loments coiled; leaflets 10–18.	Prosopis pubescens
3	Loments straight or curved; leaflets 12–60.	> 4
4	Leaflets alternate.	Prosopis laevigata
4	Leaflets opposite.	> 5
5	Leaflets 5–18 mm apart, blades (15–)20–63 mm, surfaces glabrous.	Prosopis glandulosa
5	Leaflets 3–4 mm apart, blades 4–13 mm, surfaces pubescent.	Prosopis velutina