A tree, 18°—20° high, with a short stout contorted trunk sometimes 20′ in diameter and divided near the ground into several upright branches, and branchlets reduced to slender sharp spines coated with fine pubescence, bearing minute nearly triangular scarious caducous bracts, marked by occasional glandular fistules, and developed from stouter branches hoary-pubescent when young, becoming glabrous in their third year and covered with pale brown bark roughened with lenticels and as it exfoliates showing the pale green inner bark; more often a low rigid intricately branched shrub. Bark of the trunk dark gray-brown, nearly ¼′ thick, deeply furrowed, and roughened on the surface by small persistent scales. Wood light, soft, rather close-grained, walnut-brown in color, with nearly white sapwood of 12—15 layers of annual growth.
Distribution. Valley of the lower Gila River, Arizona, through the Colorado Desert to San Felipe and Palm Springs, Riverside County, California, and southward into Sonora and Lower California.
15. ROBINIA L. Locust.
Trees or shrubs, with slender terete or slightly many-angled zigzag branchlets, without a terminal bud, minute naked subpetiolar depressed-globose axillary buds 3 or 4 together, superposed, protected collectively in a depression by a scale-like covering lined on the inner surface with a thick coat of tomentum and opening in early spring, its divisions persistent during the season on the base of the branchlet developed usually from the upper bud. Leaves unequally pinnate, petiolate, deciduous; leaflets entire, penniveined, stipellate, reticulate-venulose, petiolulate; stipules setaceous, becoming spinescent at maturity, persistent. Flowers on long pedicels, in short pendulous racemes from the axils of leaves of the year, with small acuminate caducous bracts and bractlets; calyx campanulate, 5-toothed or cut, the upper lobes shorter than the others, cohering for part of their length; corolla papilionaceous, petals shortly unguiculate, inserted on a tubular disk glandular on the inner surface and connate with the base of the calyx-tube; standard large, reflexed, barely longer than the wing- and keel-petals, naked on the inner surface, obcordate, reflexed; wings oblong-falcate, free; keel-petals incurved, obtuse, united below; stamens 10, inserted with the petals, the 9 inferior united into a tube often enlarged at base and cleft on the upper side, the superior stamen free at the base and connate in the middle with the staminal tube, or finally free; anthers ovoid; ovary inserted at the base of the calyx, linear-oblong, stipitate; style subulate, inflexed, bearded along the inner side near the apex, with a small terminal stigma; ovules numerous, suspended from the inner angle of the ovary, in two ranks, superposed. Legumes in drooping many-fruited racemes, many-seeded, linear, compressed, almost sessile, 2-valved, the seed-bearing suture narrow-winged; valves thin and membranaceous. Seed oblong-oblique, transverse, attached by a stout persistent incurved funicle enlarged at the point of attachment to the placenta; seed-coat thin, crustaceous; albumen thin, membranaceous; cotyledons oval, fleshy; radicle short, much reflexed, accumbent.
Robinia with seven or eight species is confined to the United States and Mexico; of the species found in the United States three are arborescent.
The generic name commemorates the botanical labors of Jean and Vespasien Robin, arborists and herbalists of the kings of France in the sixteenth and seventeenth centuries.
CONSPECTUS OF THE ARBORESCENT SPECIES OF THE UNITED STATES.
Legume without glandular hairs; flowers white.1. [R. Pseudoacacia] (A, C). Legume glandular-hispid (in the arborescent form of No. 2); flowers rose color. Glands not viscid.2. [R. neo-Mexicana] (F, H). Glands exuding a clammy sticky substance.3. [R. viscosa] (A).
1. [Robinia Pseudoacacia] L. Locust. Acacia. Yellow Locust.
