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.
CONSPECTUS OF THE NORTH AMERICAN ARBORESCENT SPECIES.
Legume compressed or ultimately convex; pinnæ 12—22-foliolate.1. [P. juliflora] (C, E, G, H). Legume thick, spirally twisted; pinnæ 10—16-foliolate.2. [P. pubescens] (E, F, G, H).
1. [Prosopis juliflora] DC. Mesquite. Honey Locust.
Leaves with 2 or rarely 4 pinnæ, and slender terete petioles abruptly enlarged and glandular at base; stipules linear, acute, membranaceous, deciduous. Flowers appearing in successive crops from May to the middle of July, fragrant, about 1/12′ long, on short pedicels, in slender cylindric spikes 1½′—4′ long, on stout peduncles ½′—¾′ in length; calyx glabrous or puberulous, about one fourth as long as the narrowly oblong acute petals, glabrous or puberulous on the outer surface and covered on the inner surface toward the apex with hoary tomentum; stamens twice as long as the corolla, the dark-colored connective of the anther-cells furnished at apex with a stalked gland; ovary short-stalked, clothed with silky hairs. Fruit in drooping clusters, linear, at first flat, becoming subterete at maturity, constricted between the 10-20 seeds, straight or falcate, contracted at the ends, 4′—9′ long, ¼′—½′ wide; seeds about ¼′ long.
A low tree, with a large thick taproot descending frequently to the depth of 40°-50°, and furnished with radiating horizontal roots spreading in all directions and forming a dense mat, a trunk 6′—8′ in diameter, divided a short distance above the ground into many irregularly arranged crooked branches forming a loose straggling head, and slender branchlets at first pale yellow-green, turning darker in their second year, furnished in the axils of the leaves of their first season with short spur-like excrescences covered with chaffy scales, and armed with stout straight terete supra-axillary persistent spines ½′—2′ long, or rarely unarmed; more often a shrub, with numerous stems only a few feet high. Bark of the trunk thick, dark reddish brown, divided by shallow fissures, the surface separating into short thick scales. Wood heavy, close-grained, rich dark brown or sometimes red, with thin clear yellow sapwood; almost indestructible in contact with the soil, and largely used for fence-posts, railway-ties, the underpinnings of buildings, and occasionally in the manufacture of furniture, the fellies of wheels, and the pavements of city streets; the best fuel of the region, and largely made into charcoal. The ripe pods supply Mexicans and Indians with a nutritious food, and are devoured by most herbivorous animals. A gum, resembling gum-arabic, exudes from the stems.
Distribution. Western Texas and eastern New Mexico, and on the island of Jamaica; eastward and westward diverging into two extreme forms. These are
Prosopis juliflora var. glandulosa Cock.
Leaves 8′—10′ long, 2-pinnate, with long slender petioles, the pinnæ 12—20-foliolate; leaflets distant, linear, mostly acute, glabrous, dark green, often 2′ long and ⅛′—¼′ wide. Flowers with a usually glabrous calyx. Fruit occasionally conspicuously constricted between the seeds (f. constricta Sarg.).
A round-topped tree, often 20° high, with a trunk a foot in diameter, and long gracefully drooping branches forming a symmetrical round-topped head.
Distribution. Eastern Texas to western Louisiana (near Shreveport, Caddo Parish), western Oklahoma and southern Kansas, and southward into northern Mexico. The common Mesquite of eastern Texas; reappearing with rather shorter and more crowded leaflets in Arizona, southern California, and Lower California.
Prosopis juliflora var. velutina Sarg.
Leaves 5′—6′ long, often fascicled, 2—4-pinnate, cinereo-pubescent, with short petioles, the pinnæ 12-22-foliolate; leaflets oblong or linear-oblong, obtuse or acute, crowded, pale green, ¼′—½′ long. Flowers in densely-flowered spikes 2′—3′ long; calyx villose.
A tree, often 50° high, with a trunk 2° in diameter, covered with rough dark brown bark, and heavy irregularly arranged usually crooked branches.
Distribution. Dry valleys of southern Arizona and of Sonora.
2. [Prosopis pubescens] Benth. Screw Bean. Screw Pod Mesquite.
Leaves canescently pubescent, 2′—3′ long, with a slender petiole ⅓′—⅔′ in length, and pinnæ 1½′—2′ long and 10—16-foliolate; stipules spinescent, deciduous; leaflets oblong or somewhat falcate, acute, sessile or short-petiolulate, often apiculate, conspicuously reticulate-veined, ⅓′—⅔′ long, ⅛′ wide. Flowers beginning to open in early spring, and produced in successive crops from the axils of minute scarious bracts, in dense or interrupted cylindric spikes 2′—3′ long; calyx obscurely 5-lobed, pubescent on the outer surface, one third to one fourth as long as the narrow acute petals coated on the inner surface near the apex with thick white tomentum, and slightly puberulous on the outer surface; ovary and young fruit hoary-tomentose. Fruit ripening throughout the summer and falling in the autumn, in dense racemes, sessile, twisted with from 12—20 turns into a narrow straight spiral 1′—2′ long; seeds 1/16′ long.
A tree, 25°-30° high, with a slender trunk sometimes a foot in diameter, and terete branches canescently pubescent or glabrate when they first appear, becoming glabrous and light red-brown in their third year, and armed with stout spines ⅓′—½′ long. Bark of the trunk thick, light brown tinged with red, separating in long thin persistent ribbon-like scales. Wood heavy, exceedingly hard, close-grained, not strong, light brown, with thin lighter colored sapwood of 6 or 7 layers of annual growth; used as fuel and occasionally for fencing. The sweet, nutritious legumes are valued as fodder.
Distribution. Sandy or gravelly bottom-lands; valley of the Rio Grande in western Texas, and through New Mexico and Arizona to southern Utah and Nevada, and to San Diego County, California, and northern Mexico; attaining its largest size in the United States in the valleys of the lower Colorado and Gila Rivers, Arizona.