Leaves 8′—14′ long, with a slender puberulous petiole, and 7—19 leaflets; turning pale clear yellow late in the autumn just before falling; stipules ½′ long, linear, subulate, membranaceous, at first pubescent and tipped with small tufts of caducous brown hairs, becoming straight or slightly recurved spines persistent for many years and ultimately often more than 1′ in length; leaflets oval, rounded or slightly truncate and minutely apiculate at apex, when they unfold covered with caducous silvery pubescence, at maturity very thin, dull dark blue-green above, pale below, glabrous with the exception of the slight pubescence on the under side of the slender midrib, 1½′—2′ long and ½′—¾′ wide; petiolules stout, ⅛′—¼′ in length; stipules minute, linear, membranaceous, early deciduous. Flowers opening in May or early in June, filled with nectar, very fragrant, on slender pedicels ½′ long and dark red or red tinged with green, in loose puberulous racemes 4′—5′ long; calyx conspicuously gibbous on the upper side, ciliate on the margins, dark green blotched with red, especially on the upper side, the lower lobe acuminate and much longer than the nearly triangular lateral and upper lobes; petals pure white, with a large pale yellow blotch marking the inner surface of the standard. Fruit ripening late in the autumn, 3′—4′ long and ½′ wide, with bright red-brown valves, usually 4—8-seeded, mostly persistent until the end of winter or early spring; seeds 3/16′ long, dark orange-brown, with irregular darker markings.
A tree, 70°—80° high, with a trunk 3°—4° in diameter, small brittle usually erect branches forming a narrow oblong head, and slender terete or sometimes slightly many-angled branchlets marked by small pale scattered lenticels, coated at first with short appressed silvery white deciduous pubescence, pale green and puberulous during their first summer, becoming light reddish brown and glabrous or nearly glabrous toward autumn. Bark of the trunk 1′—1½′ thick, deeply furrowed, dark brown tinged with red, and covered by small square persistent scales. Wood heavy, exceedingly hard and strong, close-grained, very durable in contact with the ground, brown or rarely light green, with pale yellow sapwood of 2 or 3 layers of annual growth; formerly extensively used in shipbuilding, for all sorts of posts, in construction and turnery; preferred for treenails, and valued as fuel.
Distribution. Slopes of the Appalachian Mountains, central and southern Pennsylvania, to northern Georgia; in southern Illinois; now widely naturalized in the United States east of the Rocky Mountains, and perhaps indigenous as a low shrub in northeastern and western Arkansas and in Oklahoma; nowhere common; in the Appalachian forest growing singly or in small groups up to altitudes of 3500°; most abundant and of its largest size on the western slopes of the Alleghanies of West Virginia; often spreading by underground stems into broad thickets of small and often stunted trees.
Formerly much planted as an ornamental and timber tree in the eastern states; very frequently used in Europe, with numerous seminal varieties of peculiar foliage or habit, for the decoration of parks and gardens, and to shade the streets of cities.
2. [Robinia neo-mexicana] A. Gray. Locust.
In its typical form a shrub only a few feet high. The hairs on the fruit not glandular-hispid.
Distribution. Mountain cañons and plains, Grant County, New Mexico. Passing into
Robinia neo-mexicana var. luxurians Dieck.
Leaves 6′—12′ long, with a stout pubescent petiole, and 15—21 leaflets; stipules chartaceous, covered with long silky brown hairs, becoming at maturity stout slightly recurved flat brown or bright red spines sometimes 1′ or more long; leaflets elliptic-oblong, rounded or sometimes slightly emarginate at the mucronate apex, cuneate or sometimes rounded at base, 1½′ long, and 1′ broad, coated at first on the lower surface and on the margins with soft brown hairs, and silvery-pubescent on the upper surface, and at maturity thin, pale blue-green, conspicuously reticulate-veined, and glabrous with the exception of the slightly puberulous lower side of the slender midrib and stout petiolule; stipels membranaceous, ¼′ long, often recurved, sometimes persistent through the season. Flowers appearing in May, 1′ long, on slender pedicels ½′ in length and covered with stout glandular hairs, in short compact many-flowered glandular-hispid long-stemmed racemes; corolla pale rose color or sometimes almost white (f. albiflora Kusche), with a broad standard and wing-petals. Fruit 3′—4′ long, about ⅓′ wide, glandular-hispid, with a narrow wing; seeds dark brown, slightly mottled, 1/16′ long.