Monographs Details: Psorothamnus spinosus (A.Gray) Barneby
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1977. Daleae Imagines, an illustrated revision of Errazurizia Philippi, Psorothamnus Rydberg, Marine Liebmann, and Dalea Lucanus emen. Barneby, including all species of Leguminosae tribe Amorpheae Borissova ever referred to Dalea. Mem. New York Bot. Gard. 27: 1-892.
Family:Fabaceae
Synonyms:Dalea spinosa A.Gray, Asagraea spinosa (A.Gray) Baill., Parosela spinosa (A.Gray) A.Heller, Psorodendron spinosum (A.Gray) Rydb.
Description:Species Description - Small, round-headed trees, flowering as bushy shrubs at a stature of ± 1.5 m, attaining within a few years a stature of 7, exceptionally 10 m, with a single or few trunks up to 1 dm diam (mostly much less), the old bark pale gray, the repeatedly, stiffly and closely forking branches densely silvery-silky with short, forwardly appressed or sub-appressed hairs (in age rarely glabrescent and greenish), charged distally with large rounded or more prominent and prickle-shaped, orange glands, the ultimate branchlets all in reality raceme-axes tapering into a stout, glabrous brownish or yellowish thorn, the whole appearing leafless and during the greater part of the year truly so; leaf-spurs short, charged on either side with a large gland; stipules 0.2-1 mm long, broadly deltate, dorsally silky, glabrous within, deciduous; leaves of mature plants shed shortly before or after anthesis, all reduced to a terminal, petiolulate, oblanceolate or cuneate- oblanceolate, truncate-retuse, thick-textured leaflet 2-22 mm long, strigulose both sides, bluntly gland-tipped dorsally; seedling leaves, present only during the first few months of growth, broadly oblanceolate, 2-6 cm long, 0.5-2 cm wide, glaucescent, faintly 3-7-nerved, the margins glandular-crenulate or shallowly gland-toothed; racemes loosely 5-15-flowered, the axis (including the terminal spine) 1-4 cm long; bracts fugacious, ovate, 0.5-0.8 mm long, silky dorsally; pedicels 0.7-1.8 mm long, charged near apex with a pair of linear, silky bracteoles, sometimes also by a pair of glands; calyx 4.5-5.2 mm long, densely silky-strigulose, the hypanthium 1.2-0.7 mm deep, the bluntly angled and shallowly pleated tube 3-3.8 mm long, the ribs little prominent, the firm intervals charged above middle with 1 large (rarely 2, or exceptionally 0) obtuse or prickle-shaped gland, the herbaceous lobes ovate, gland-mucronulate, slightly unequal, the ventral pair largest, (1) 1.2-1.7 mm long, not or scarcely united behind the banner and the orifice therefore subsymmetrical, all recurved in age, faintly reticulate-nerved, densely silky-pubescent internally; petals indigo-blue, eglandular or rarely the banner charged with a subapical gland, glabrous; banner 6.4-7.5 mm long, its incurved claw ±1.5 mm long, the ventral face commonly ridged lengthwise and the ridges terminating in callosities, the blade obcordate, auriculate at base, strongly recurved, 5.2-6.6 mm long, ±5-7 mm wide; wings 7-8.8 mm long, the claw2.2-2.6 mm, the obovate to broadly oblanceolate, obtuse or emarginate blade 5.5-6.8 mm long, (2.4) 3-4.5 mm wide; keel 9.2-11 mm long, the claw 2.4-3.2 mm, the obovate blades 6.6-8.2 mm long, 4.2-5.4 mm wide, the auricle small or almost 0; androecium 9.5-11.5 mm long, the filaments free for 4.1-4.9 mm, the connective gland-tipped, the anthers 0.75-1.1 mm long; pod as long or slightly longer than the calyx, plumply compressed-obovoid, the firm valves pilosulous distally and charged mostly below middle with several blister-glands; ovules (3) 4-7, but only 1 or 2 developing into seeds; seeds (if 2, then superposed, not opposite) little known, ± 3 mm long, the testa smooth, brown, purple-speckled. — Collections: 53 (o).

Distribution - Sandy and bouldery washes in the Larrea belt, mostly below 240 m (800 ft) but up to 400 m in extreme s. Nevada and 430 m in Baja California, descending in Salton Depression to -70 m, widespread over the Colorado Desert but apparently most abundant along its western periphery, from Coachella Valley e.-ward to both banks of the Colorado River, there n. just into the s. point of Nevada and the s. margins of Mohave Desert near the sink of Mohave River, s.-e. to the big bend of Gila River in Maricopa County, Arizona, to extreme n.-w. Sonora, and along the foot of Sierra San Pedro Martir in Baja California (Edo) into the Idria deserts, reaching nearly to 28° S between Calamajue and Calmalli, and in the Gulf as far as Isla San Angel de la Guardia near 29° 30 (but unknown from these latitudes in Sonora).- Flowering late May to mid-July, in fruit July and August, flowering again, rarely and less prolifically, in October-November. Map (essentially complete in outline except for extension n. along Colorado River into s. Nevada)

Discussion:

The Smoke Tree, Ps. spinosus, an arborescent bush characteristic of the bed or banks of washes and intermittent streams on the out wash fans of low desert mountains, is familiar to most travellers in its leafless and flowerless state, rising in distant view as a puff of silvery vapor from the vivid greens of larrea and palo verde but resolving at close quarters into a lattice of stiffly divaricate branchlets running out into smooth stout thorns. The leaves of the adult tree, produced only on young growth following fall or winter rains, are small, simple, and fugacious, adding little by way of mass to the rounded head or to the shadow cast by it. For three fourths of the year the task of photosynthesis falls to the branchlets of the current year, which remain green beneath their gray or silvery vesture. Seedlings, however, bear during their first season ample oblanceolate leaf-blades up to 5 cm long, permitting rapid growth during the few weeks when water is available to the young root. The Smoke Tree has been described as shy-flowering, but (disregarding years of extreme drought) is only late- flowering, and seldom collected in flower or fruit. Flower-buds do not form until mid-May or early June: they are, however, extremely numerous, when expanded clothing all the young growth with a robe of vivid indigo. Seed is abundant but hard-shelled, and seems to germinate only after it has been ground by water-moved sands and gravels of the torrent bed, sands which later overwhelm and smother many of the young plants. Despite its hard, close-grained wood and considerable stature the Smoke Tree is said to mature rapidly and perish early. On the desert the fallen branches are used for fuel, when burned giving an aromatic smoke.

Handsome portraits of the often photographed Smoke Tree may be seen in McMinn, Illustrated Manual of California Shrubs, fig. 241; and Jaeger, Desert Wild Flowers, fig. 236 and in splendid color in de Wit, Knaurs Pflanzenreich in Farben 1: fig. 181. 1964. Best of all is Faxon’s superb lithograph in Sargent, Silva N. Amer. 3: t. CXI. 1892.

Distribution:United States of America North America| California United States of America North America| Nevada United States of America North America|

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