Leaves 4′-7′ long and 3′-4′ wide, with a slender petiole usually marked by a large dark oblong gland between the somewhat enlarged base and the lowest pair of the 30-36 nearly sessile crowded pinnæ, each with 30-60 pairs of leaflets, and minute caducous stipules, when they unfold covered like the peduncles and flower-buds with dense hoary tomentum, and at maturity puberulous on the petiole and rachis; leaflets linear, acute, rather oblique at base by the greater development of the upper side, sessile or very short-petiolulate, pale bright green, ⅙′—¼′ long. Flowers sessile, fragrant, in heads ½′ in diameter, appearing in succession as the branches grow from early spring to midsummer, on slender peduncles 1′—1½′ long and fascicled in the axils of upper leaves; calyx one fourth as long as the acute petals and like them pilose on the outer surface; stamens twice as long as the petals; ovary coated with long pale hairs. Fruit conspicuously thick-margined, 4′-14′ long, long-stalked, tipped with a short straight or recurved point, usually in pairs on a peduncle thickened at apex; seeds 5/16′ long.
A tree, 50°-60° high, with a straight trunk 18′-20′ in diameter, separating 20°-30° from the ground into slender spreading branches forming a loose round head, and branchlets at first more or less striately grooved and thickly coated with pulverulent caducous tomentum, becoming at the end of a few weeks terete, pale cinnamon-brown and puberulous. Bark about ¼′ thick, bright cinnamon-brown, and roughened by thick persistent scales. Wood heavy, hard, very close-grained, rich dark brown, with thin clear yellow sapwood of 2 or 3 layers of annual growth; considered valuable, and sometimes manufactured into lumber.
Distribution. Rich moist soil of river banks and the borders of lagoons and small streams; valley of the lower Rio Grande; in Texas only for a few miles near its mouth; more abundant from Matamoras to Monterey in Nuevo Leon; and southward to the neighborhood of the City of Mexico.
Occasionally planted as a shade and ornamental tree in the towns of the lower Rio Grande valley and in New Orleans, Louisiana.
5. PROSOPIS L. Mesquite.
Trees or shrubs, with branches without a terminal bud and armed with geminate supra-axillary persistent spines, and small obtuse axillary buds covered with acute apiculate dark brown scales. Leaves alternate on branches of the year and fascicled in earlier axils, deciduous, usually 2 rarely 3-4-pinnate, with many-foliolate pinnæ; petioles glandular at apex with a minute gland, and tipped with the small spinescent rachis; stipules linear, membranaceous or spinescent, deciduous. Flowers greenish white, nearly sessile, in axillary pedunculate spikes; calyx campanulate, 5-toothed, or slightly 5-lobed, deciduous; petals 5, connate below the middle or ultimately free, glabrous or tomentose on the inner surface toward the apex, sometimes puberulous on the outer surface; stamens 10, free, inserted with the petals on the margin of a minute disk adnate to the calyx-tube, those opposite the lobes of the calyx rather longer than the others; filaments filiform; anthers oblong, versatile, their connective tipped with a minute deciduous gland, the cells opening by marginal sutures; ovary stipitate, villose; style filiform, with a minute terminal stigma. Legume linear, compressed, or subterete, straight or falcate, or contorted or twisted into a more or less regular spiral, indehiscent; the outer coat thin, woody, pale yellow, inclosing a thick spongy inner coat of sweet pulp containing the seeds placed obliquely and separately inclosed, their envelopes forming nut-like joints. Seeds oblong, compressed, the hilum near the base; seed-coat crustaceous, light brown, lustrous; embryo surrounded by a layer of horny albumen; radicle short, slightly exserted.
Prosopis is distributed in the New World from southern Kansas to Patagonia, and in the Old World is confined to tropical Africa, and to southwestern and tropical Asia. Sixteen or seventeen species have been distinguished. Of the three species found in the territory of the United States two are small trees.
Prosopis produces hard durable wood, particularly valuable as fuel, and the pods are used as fodder.
The generic name is from προσωπίς, employed by Dioscorides as a name of the Burdock.