4. LEUCÆNA Benth.
Trees or shrubs, with slender unarmed branches. Leaves persistent, abruptly bipinnate, with numerous pinnæ and small leaflets in many pairs, petiolate, the petioles often furnished with a conspicuous gland below the lower pair of pinnæ; stipules minute and caducous, or becoming spinescent and persistent. Flowers minute, white, mostly perfect, sessile or short-pedicellate, in the axils of small peltate bracts villose at apex, in globose many-flowered pedunculate heads, the peduncles in axillary fascicles or in leafless terminal racemes; calyx tubular-campanulate, minutely 5-toothed; petals 5, free, acute or rounded at apex, narrowed at base; stamens 10, free, inserted under the ovary, exserted; filaments filiform; anthers oblong, versatile; ovary stipitate, contracted into a long slender style, with a minute terminal slightly dilated stigma. Legume many-seeded, stipitate, linear, compressed, dehiscent, the valves thickened on the margins, rigid, thin, continuous within, their outer coat thin and papery, dark-colored, the inner rather thicker, woody, pale brown. Seeds obovoid, compressed, transverse, the hilum near the base, suspended on a long slender funicle; seed-coat thin, crustaceous, brown and lustrous; embryo inclosed on its two sides by a thin layer of horny albumen; radicle slightly exserted.
Leucæna with nine or ten species is confined to the warmer parts of America from western Texas to Venezuela and Peru, and to the islands of the Pacific Ocean from New Caledonia to Tahiti, where one species has been recognized. Of the indigenous species found in the territory of the United States, three are arborescent. Leucæna glauca L., a small tree or shrub, cultivated in all warm countries, and a native probably of tropical America, is now naturalized on Key West, Florida.
The generic name, from λευχαίνω, refers to the color of the flowers.
CONSPECTUS OF THE NORTH AMERICAN SPECIES.
Peduncles bibracteolate at apex; stipules becoming spinescent. Leaves 10—14-pinnate; pinnæ with 15—30 pairs of leaflets; blade of the bract of the flower produced into a short point.1. [L. Greggii] (E). Leaves 2—4-pinnate; pinnæ with 4—8 pairs of leaflets; blade of the bract of the flower produced into a long slender villose tip.2. [L. retusa] (E). Peduncles without bracts; stipules minute, caducous; leaves 30—36-pinnate; pinnæ with 30—60 pairs of leaflets.3. [L. pulverulenta] (E).
1. [Leucæna Greggii] S. Wats.
Leaves 6′—7′ long and broad, with a slender rachis furnished on the upper side with a single elongated bottle-shaped gland between the stalks of each pair of pinnæ; pinnæ 10—14, remote, short-stalked, with 15—30 pairs of leaflets; stipules gradually narrowed into a long slender point, becoming rigid and spinescent, ⅓′ to nearly ½′ long and persistent for two or three years; leaflets lanceolate, acute or acuminate, often somewhat falcate, nearly sessile or short-petiolulate, full and rounded toward the base on the lower margin, nearly straight on the upper margin, gray-green, ultimately nearly glabrous, ¼′—⅓′ long, about ⅛′ wide, with a narrow midvein and obscure lateral nerves. Flowers on slender pedicels, in heads ¾′—1′ in diameter, on stout peduncles 2′—3′ long furnished at apex with 2 irregularly 3-lobed bracts, and solitary or in pairs; calyx coated with hairs only near the apex, much shorter than the spatulate glabrous more or less boat-shaped petals; ovary villose with a few short scattered hairs. Fruit 6′-8′ long, ⅓′—½′ wide, narrowed below into a short stout stipe, acuminate and crowned at apex with the thickened style, ⅓′—¾′ long, cinereo-pubescent until nearly fully grown, becoming nearly glabrous at maturity, much compressed, with narrow wing-like margins; seeds conspicuously notched by the hilum, ½′ long and ⅓′ wide.
A tree, 15°-20° high, with a stem 4′—5′ in diameter, and stout zigzag red-brown branchlets marked by numerous pale lenticels, coated at first with short spreading lustrous yellow deciduous hairs found also on the young petioles and lower surface of the unfolding leaflets, the peduncles of the flower-heads and their bracts. Bark about ⅜′ thick, dark brown, divided into low ridges and broken on the surface into small closely appressed persistent scales. Wood heavy, hard, close-grained, rich brown streaked with red, with thin clear sapwood.
Distribution. Mountain ravines and the steep banks of streams; western Texas from the valley of the upper San Saba River to that of Devil’s River; and southward into Mexico.
2. [Leucæna retusa] Benth.
Leaves 3′ or 4′ long and 4′ or 5′ wide, with a slender petiole and rachis and 2-4 pairs of pinnæ 6′-10′ long, remote, long-stalked, with 4-8 pairs of short-stalked leaflets furnished between their stems with a single globose white gland found also occasionally on the upper side of the rachis between the stems of the pinnæ; stipules ovate, gradually narrowed into a long slender tip, ½′ in length, often persistent through the season; leaflets obliquely obovate or elliptic, rounded and apiculate at apex, obliquely rounded or cuneate at the unsymmetric base, entire, short-petiolulate, villose-pubescent like the rachis and petiole when they first appear, soon, glabrous, and at maturity thin, blue-green, ¾′—1′ long and ⅓′—½′ wide, with a slender midrib, and prominent veins extending obliquely toward the apex of the leaflet, those of the lowest pair more prominent and starting from near its base. Flowers short-stalked in the axil of a peltate bract, its blade produced into a long slender villose tip, appearing continuously from April until October in dense globose heads ¾′ in diameter, on villose bibracteolate axillary, single or fascicled peduncles 1½′—3′ in length; calyx thin, tubular, 5-toothed at apex; petals narrow-oblong, hardly longer than the calyx; stamens 10, shorter than the bract of the flower; anthers glabrous. Fruit solitary or clustered, on a puberulous peduncle 3′-5′ in length, 6′-10′ long, ⅓′—½′ wide, gradually narrowed below into a stout stipe, the acuminate apex terminating in the thickened persistent style, glabrous and dark reddish brown; seeds ⅓′ long and ¼′ wide.
A tree, occasionally 25° high, with a trunk 6′-8′ in diameter, and slender branchlets pubescent when they first appear, becoming puberulous and orange-brown or reddish brown at the end of their first season; more often a shrub.
Distribution. Texas; steep rocky hillsides, and on the summits of limestone bluffs; (Uvalde, Valverde, Kemble, Real and Jeff Davis Counties).
3. [Leucæna pulverulenta] Benth. Mimosa.
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.