596 TREES OF NORTH AMERICA 



A tree, rarely 30 high, with a trunk 10'-12' in diameter, numerous spreading branches, 

 and striately angled puberulous or in Texas glabrous pale brown branchlets faintly tinged 

 with red and armed with stout recurved infrastipular spines flat at base, and j long and 

 broad. Bark of the trunk about f thick, furrowed, the surface separating into thin nar- 



Fig. 546 



row scales. Wood heavy, very hard, strong, close-grained, durable, rich brown or red, 

 with thin light yellow sap wood of 5 or 6 layers of annual growth. 



Distribution. Dry gravelly mesas, the sides of low canons and the banks of moun- 

 tain streams; valley of the Rio Grande, western Texas, through southern New Mexico 

 and Arizona to southern California, ranging northward in Arizona to the rim of the Grand 

 Canon of the Colorado River, and to Clark County, Nevada; in northern Mexico, and in 

 Lower California to the eastern base of the San Pedro Martir Mountains. 



4. LEUC^ENA Benth. 



Trees or shrubs, with slender unarmed branches. Leaves persistent, abruptly bipin- 

 nate, with numerous pinnae and small leaflets in many pairs, petiolate, the petioles often 

 furnished with a conspicuous gland below the lower pair of pinnae; 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 ter- 

 minal 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, ex- 

 serted; 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, w r oody, pale brow r n. 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. 



Leucaena 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. Leucaena 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 ^v-^aivu, refers to the color of the flowers. 



