9. PARKINSONIA L.
Trees or shrubs, with smooth thin bark and terete branches often armed with simple or 3-forked spines. Leaves abruptly bipinnate, alternate or fascicled from earlier axils, short-petiolate, the rachis short and spinescent, with 2—4 secondary elongated rachises bearing numerous minute opposite entire leaflets without stipels; stipules short, persistent and spinescent, or caducous. Flowers perfect on thin elongated jointed pedicels from the axils of minute caducous bracts, in slender axillary solitary or fascicled racemes; calyx short-campanulate, 5-lobed, the lobes slightly imbricated or subvalvate in the bud, narrow, membranaceous, nearly equal, becoming reflexed, deciduous; petals bright yellow, unguiculate, much longer than the lobes of the calyx, spreading, the upper petal rather broader than the others and glandular at the base of the claw; stamens 10, inserted in 2 rows on the margin of the thin disk, free, slightly declinate, those of the outer row opposite the sepals and rather longer than the others; filaments villose below the middle, the upper filament enlarged at base and gibbous on the upper side; anthers uniform, versatile; ovary short-stipitate, pilose, contracted into a slender filiform incurved style infolded in the bud and tipped with a minute stigma; ovules numerous, suspended from the inner angle of the ovary. Legume linear, torulose, acuminate at the ends, 2-valved, the valves thin, convex by the growth of the seeds, contracted between and beyond them, longitudinally striate. Seeds oblong, suspended longitudinally on a slender funicle; hilum minute, near the apex; seed-coat thin, crustaceous, light brown; embryo inclosed on the sides only by thick layers of horny albumen; cotyledons oval, flat, slightly fleshy, the radicle very short and straight.
Parkinsonia, with four species, is confined to the warm parts of America and to southern Africa. Two species occur within the limits of the United States.
The genus is named for John Parkinson (1567—1650), an English botanical author, and herbalist to James I.
CONSPECTUS OF THE NORTH AMERICAN SPECIES.
Flowers in long slender racemes; petals imbricated in the bud; stamens shorter than the petals; legume 1—8-seeded, 12′—18′ long; leaves 7′—8′ long; rachis of the pinnæ flat, wing-margined, 50—60-foliolate; branches with spines.1. [P. aculeata] (G, H). Flowers in short racemes; petals valvate in the bud; stamens longer than the petals; legume 1—2-seeded; leaves about 1′ long; rachis of the pinnæ terete, 8—12-foliolate; branches without spines.2. [P. microphylla] (G, H).
1. [Parkinsonia aculeata] L. Retama. Horse Bean.
Leaves of two forms, short-petiolate, persistent, light green and glabrous, except for a few hairs on the lower part of the young secondary rachis, 12′—18′ long; primary leaves on young branches, with 2—4 pinnæ, and a spinescent rachis developing into a stout ridged persistent short-pointed chestnut-brown spine 1′—1½′ long and marked near the base by the prominent scars left by the fall of the pinnæ; stipules persistent, appearing as lateral spiny branches on the spines; secondary leaves fascicled from the axils of the primary leaves, nearly sessile with a short terete spinescent rachis and 2 pinnæ; pinnæ flat, 12′—18′ in length, wing-margined, acute at apex, with 25—30 pairs of ovate or obovate petiolulate leaflets, 1/16′—⅛′ long. Flowers appearing on the growing branches during the spring and summer, and in the tropics throughout the year, on slender pedicels ⅓′—½′ in length, in slender erect racemes 5′—6′ long; petals bright yellow, the upper one marked near the base on the inner surface with conspicuous red spots; stamens shorter than the petals. Fruit hanging on pedicels ½′—¾′ in length, in graceful racemes, 2′—4′ long, long-pointed, dark orange-brown, slightly pilose, compressed between the remote seeds; seeds ⅓′ long, nearly terete, with thick albumen and a bright yellow embryo.
A tree, 18°—30° high, with a trunk sometimes a foot in diameter, usually separating 6°—8° from the ground into slender spreading somewhat pendulous branches forming a wide graceful head, and slightly zigzag branchlets puberulous and yellow-green during their first season, becoming glabrous, gray or light orange color and roughened by lenticels in their second and third years. Bark of the trunk about ⅛′ thick, brown tinged with red, the generally smooth surface broken into small persistent plate-like scales. Wood heavy, hard, close-grained, with very thick lighter colored sapwood tinged with yellow.
Distribution. Low moist soil, valley of the lower Rio Grande, Texas; common in northern Mexico and in the valley of the lower Colorado River, Arizona; widely distributed in Lower California; naturalized on Key West, the Bahamas, the West Indian islands, and in many other tropical countries.
Cultivated in most warm countries as an ornament of gardens, and to form hedges.
2. [Parkinsonia microphylla] Torr.
Leaves 1′ long, pale, densely tomentose when they unfold, pubescent at maturity, deciduous at the end of a few weeks; petiole ¼′ long; rachis short, rarely spinescent; leaflets in 4—6 pairs, distant, entire, sessile, broad-oblong or nearly orbicular, obtuse or somewhat acute at apex, oblique at base, ⅙′ long; stipules caducous. Flowers opening in May or early June before the leaves, on slender pedicels, in racemes 1′ or less long from the axils of leaves of the previous year, pale yellow; stamens longer than the petals. Fruit persistent on the branches for at least a year, frequently 1 or 2, rarely 3-seeded, 2′—3′ long, slightly puberulous, especially toward the base, with a long acuminate often falcate apex; seeds compressed, ⅓′ long, with a bright green embryo.
An intricately branched tree, occasionally 20°—25° high, with a trunk a foot in diameter, and stout pale yellow-green rigid branchlets terminating in a stout spine, covered at first with deciduous tomentum, slightly puberulous during their first and second seasons, and often marked by the persistent scales of undeveloped buds. Bark dark orange color, generally smooth, although sometimes roughened by scattered clusters of short pale gray horizontal ridges, becoming on old trees ¼′ thick; more often a shrub, frequently only a few feet tall. Wood heavy, hard, close-grained, dark orange-brown streaked with red, with thick light brown or yellow sapwood of 25—30 layers of annual growth.
Distribution. Deserts of southern Arizona and adjacent regions of California and Sonora, and in northern Lower California; known to attain the size and habits of a tree only in the neighborhood of Wickenburg, Maricopa County, Arizona.