LEGUMINOSZ. SILVA OF NORTH AMERICA. 91 
PARKINSONIA MICROPHYLLA. 
FLoweErs in short racemes. Legumes 1 to 3-seeded. Leaves short, the rachises 
of the pinne terete, 8 to 12-foliolate. Branches unarmed. 
Parkinsonia microphylla, Torrey, Pacific R. R. Rep. iv. 136. — Brewer & Watson, Bot. Cal. i. 162.— Hemsley, 
82; Bot. Mex. Bound. Surv. 59.— Walpers, Ann. vii. Bot. Biol. Am. Cent. i. 327. — Sargent, Forest Trees N. 
812. — Gray, Ives’ Rep. 11. — Bentham, Martius Fi. Am. 10th Census U. S. ix. 60. 
Brasil. xv. pt. ii. 78. — Watson, Proc. Am. Acad. xi. 
A low intricately branched tree, occasionally twenty or twenty-five feet in height, with a trunk a 
foot in diameter, and straight rigid branchlets terminating in stout spines ; or more often a shrub with 
many stems from three to ten feet high. The bark on old trees is a quarter of an inch thick, dark 
orange-colored, and generally smooth, although sometimes roughened by scattered clusters of short light 
gray horizontal ridges. The branchlets are stout, pale yellow-green, covered at first with deciduous 
tomentum, slightly puberulous during their first and second seasons, and often marked by the persistent 
scales of undeveloped buds. The leaves are an inch long, pale, densely tomentose when they unfold, 
pubescent at maturity, and deciduous at the end of a few weeks after their appearance; the rachis is 
short, rarely spinescent, or more commonly wanting; the rachises of the pinne are slightly grooved on 
the upper side and are jointed at the points of attachment of the leaflets which are distant, entire, 
sessile, broadly oblong or nearly orbicular, obtuse or somewhat acute at the apex, oblique at the base, 
and a sixth of an inch long. The flowers, which are a third of an inch across when expanded, are 
borne on slender pedicels in racemes an inch or less in length developed from the axils of leaves of the 
previous year ; they are pale yellow, with exserted stamens, and open in May or early June before the 
new growth and the leaves appear. The legumes, which probably hang on the branches for at least a 
year, are frequently one, and rarely three-seeded ; they are two or three inches long, slightly puberulous, 
especially towards the base, and are contracted at the two ends, the long acuminate apex being often 
falcate. The seed is a third of an inch in length, with a pale brown testa and a bright green embryo. 
Parkinsonia microphylla inhabits the deserts of southern Arizona and the adjacent regions of 
California, Sonora, and Lower California. 
The wood is heavy, hard, and close-grained, with numerous thin conspicuous medullary rays and 
many large scattered open ducts. It is dark orange-brown streaked with red, with thick light brown or 
yellow sapwood composed of twenty-five or thirty layers of annual growth. The specific gravity of 
the absolutely dry wood is 0.7449, a cubic foot weighing 46.42 pounds. 
Parkinsonia microphylla is nowhere common, and it is only known to attain the size and habit 
of a tree in the neighborhood of Wickenburg in Arizona. It appears to have been first discovered, 
probably in the valley of the Colorado River, by Dr. Thomas Coulter in 1832, although it was not 
described until many years later, when it was rediscovered by the members of the Mexican Boundary 
Survey Commission. 
