Argentine Screwbean

Perennial, Shrubs, Woody throughout, Nodules present, Stems erect or ascending, Stems or branches arching, spreading or decumbent, Stems 1-2 m tall, Stems greater than 2 m tall, Trunk or stems armed with thorns, spines or prickles, Stems solid, Stems or young twigs glaucous, Stems or young twigs glabrous or sparsely glabrate, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves clustered on spurs or fasicles, Leaves petiolate, Extrafloral nectary glands on petiole, Stipules inconspicuous, absent, or caducous, Stipules persistent, Stipules free, Stipules spinose or bristles, Leaves compound, Leaves bipinnate, Leaf or leaflet margins entire, Leaflets opposite, Leaflets 10-many, Leaves glabrous or nearly so, Inflorescences globose heads, c apitate or subcapitate, Inflorescence axillary, Inflorescence or flowers lax, declined or pendulous, Flowers sessile or nearly so, Flowers actinomorphic or somewhat irregular, Calyx 5-lobed, Calyx glabrous, Petals united, valvate, Petals greenish yellow, Stamens 9-10, Stamens completely free, separate, Stamens long exserted, Filaments glabrous, Style terete, Fruit a legume, Fruit unilocular, Fruit freely dehiscent, Fruit oblong or ellipsoidal, Fruit twisted, Fruit spirally coiled or contorted, Fruit coriaceous or becoming woody, Fruit exserted from calyx, Fruit internally septate between the seeds, Fruit compressed between seeds, Fruit glabrous or glabrate, Fruit 3-10 seeded, Fruit 11-many seeded, Seeds embedded in gummy or spongy pulp, Seed with elliptical line or depression, pleurogram, Seeds ovoid to rounded in outline, Seed surface smooth, Seeds olive, brown, or black.

Prosopis strombulifera is a species of mesquite or algarrobo, a shrub in the legume family. It is known by the English common names Argentine screwbean and creeping screwbean and the Spanish common name retortuño. This shrub is native to Argentina, where it grows in arid and saline soils. It became well known in California after it was introduced to Imperial County and took hold in the wild, growing as an invasive noxious weed. The plant grows from a network of long, spreading roots and may grow to three meters in height. Many plants may grow together in an area, forming a monotypic stand. The shrub has waxy-textured leaves made up of a pair of leaflets which are each divided into several pairs of secondary leaflets each up to a centimeter long. Whitish spines up to 2 cm long appear near the leaf bases. The inflorescence is a spherical head of many very narrow tubelike yellow flowers, the head measuring about 1.5 cm wide. The fruit is a bright yellow seed pod coiled tightly into a cylindrical stick up to 5 cm long. It contains several greenish seeds, each about 0.5 cm long.