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.
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.
A tree, sometimes 20°—25° high, with a trunk 6′—8′ in diameter, and branchlets at first pale and coated with rusty brown glandular hairs increasing in length during the summer, and slightly puberulous, bright reddish brown, often covered with a glaucous bloom, and marked by a few small scattered pale lenticels during their first winter. Bark of the trunk thin, slightly furrowed, light brown, the surface separating into small plate-like scales. Wood heavy, exceedingly hard, strong, close-grained, yellow streaked with brown, with light yellow sapwood of 4 or 5 layers of annual growth.
Distribution. Banks of mountain streams; valley of the Purgatory River, Colorado, through northern New Mexico and Arizona to southern Utah; on the Santa Catalina and Santa Rita Mountains, southern Arizona up to altitudes of 7000°; probably of its largest size near Trinidad, Las Animas County, Colorado.
Occasionally cultivated as an ornamental tree in the eastern states, and in western Europe.
× Robinia Holdtii Beiss, a hybrid of Robinia neo-mexicana var. luxurians and R. Pseudoacacia, has appeared in a Colorado nursery and is occasionally cultivated.
3. [Robinia viscosa] Vent. Clammy Locust.
Leaves 7′—12′ long, with a stout nearly terete dark glandular-hispid clammy petiole, and 13—21 leaflets; stipules subulate, chartaceous, often deciduous or developing into short slender spines; leaflets ovate, sometimes acuminate, mucronate, rounded or pointed at apex, and cuneate at base, when they unfold covered below with soft white pubescence, and slightly puberulous above, and at maturity dark green and glabrous on the upper surface, pale and pubescent on the lower surface, especially on the slender yellow midrib and primary veins and on the stout glandular-hispid petiolule, 1½′—2′ long and ⅔′ wide; stipels slender, deciduous. Flowers ⅔′ long, almost inodorous, appearing in June, on slender hairy pedicels from the axils of large lanceolate acuminate dark-red bracts contracted at apex into a long setaceous point exserted beyond the flower-buds and mostly deciduous before the flowers open, in short crowded glandular-hispid racemes; calyx dark red, coated on the outer surface and on the margins of the subulate lobes with long pale hairs; corolla pale rose or flesh color, with a narrow standard marked on the inner face by a pale yellow blotch, and broad wing-petals. Fruit narrow-winged, glandular-hispid, 2′—3½′ long; seeds ⅛′ long, dark reddish brown and mottled.
A tree, 30°—40° high, with a trunk 10′—12′ in diameter, slender spreading branches, and dark reddish brown branchlets covered with conspicuous dark glandular hairs exuding, like those on the petioles and legumes, a clammy, sticky substance, during the first winter bright red-brown, covered with small black lenticels and very sticky, becoming in their second year light brown and dry; or a shrub, often only 5°—6° tall. Bark of the trunk ⅛′ thick, smooth, dark brown tinged with red. Wood heavy, hard, close-grained, brown, with light yellow sapwood of 2 or 3 layers of annual growth.
Distribution. Mountains of North and South Carolina up to altitudes of 3000°, and now naturalized in many parts of the United States east of the Mississippi River and as far north as eastern Massachusetts.
Often planted as an ornament of parks and gardens in all countries with a temperate climate.