Monographs Details: Psorothamnus scoparius (A.Gray) Rydb.
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 scoparia A.Gray, Parosela scoparia (A.Gray) A.Heller, Dalea scoparia f. suberosea Cockerell, Parosela scoparia (A.Gray) A.Heller f. scoparia
Description:Species Description - Sparsely leafy, in late summer almost leafless broomlike shrubs or subshrubs up to 1 m tall, with many pliantly erect and incurved-ascending, freely forking stems densely gray-strigulose with short, appressed or subappressed, retrorse, partly scalelike hairs and thickly charged with small orange blister-glands, the sparse deciduous foliage greenish-gray, more thinly stigulose than the stems with antrorsely subappressed hairs, the inflorescence gray-pilosulous; leaf-spurs 0.2-1 mm long; stipules subulate, 0.3-0.7 mm long, livid-glandular and glabrous at tip, deciduous; post-petiolular glands 0, or in 3-foliolate leaves small and prominent; leaves (2) 4-20 mm long, mostly simple, composed of a short petiolule and a terminal, linear-oblanceolate, retuse, thick-textured, folded leaflet prominently tuberculate beneath, a few (but not on all plants) developing a petiole+rachis up to 5 mm long bearing at apex a terminal and 2 much smaller but otherwise similar leaflets; peduncles terminal to all ultimate branchlets, 0.5-9 cm long; racemes short but not dense, mostly ± 5-15-flowered, ovate in outline, without petals (7) 8-10 mm diam, the hirsutulous axis becoming (1) 3-18 mm long, sometimes a few flowers scattered below the main spike; bracts early deciduous, papery, ovate- or oblanceolate-acuminulate, gland-tipped, pilosulous dorsally, 1.5-2.5 mm long; pedicels thick, 0-0.4 (0.7) mm long, densely pilosulous, charged with a pair of orange glands distally; calyx 3.5-4.5 mm long, densely gray-pilosulous, subspathaceous, the tube (measured to a dorsal sinus) 2.2-3 mm long, the ribs moderately prominent, the sub- membranous intervals charged with 1 row of (1) 2-5 orange glands, the ovate teeth unequal, the ventral pair longest and broadest, united to within 1 mm of tips but (1) 1.3-2 mm long measured from a lateral sinus, the dorsal tooth shortest and narrowest, all charged at tip and on each lateral margin with a blunt gland; petals (deciduous) vivid blue or blue-violet (exceptionally white), all or all but keel charged with apical glands; banner 6.4-9 mm long, the forwardly arched claw 2-2.7 mm, the oblong- obovate, basally cordate, apically notched blade 5-6.6 mm long, 3.6-4.2 mm wide; wings 7.1-9.1 mm long, the claw 2.1-2.8 mm, the narrowly oblong-oblanceolate, obliquely notched blade 5-6.7 mm long, 1.7-2.1 mm wide; keel 6.1-8.3 mm long, the claws 1.8-2.9 mm, the obliquely obovate, glabrous or thinly puberulent blades (4.2) 4.6-5.8 mm long, 2.1-3.5 mm wide; androecium 10-merous, 5.5-8.5 mm long, the longer filaments free for 2.3-2.6 mm, the connective gland-tipped, the anthers 0.6-0.85 mm long; pod slightly exserted, ± 4 mm long, glabrous at base, pilosulous and gross-glandular distally; seed castaneous, sometimes purple-speckled, 2.1 -2.7 mm long; n = 10 (Spellenberg, 1973). — Collections: 44 (vi).

Distribution - Dunes and sandy river-beds, locally abundant, 1100-1530 m (± 3670-5100 ft), very common along the Rio Grande from near Albuquerque, Bernalillo County, New Mexico downstream to El Paso and immediately adjoining Hudspeth counties, Texas, in New Mexico interruptedly e. to the White Sands in Otero County, and w. to Luna County and (isolated) the Wilcox playa in Cochise County, Arizona, s. to the great dunes of n. Chihuahua in mpos. C. Juarez and Villa Ahumada; apparently disjunct around margins of Bolson de Mapimi in w.-centr. Coahuila (Mohovano; Sa. del Rey) and immediately adjoining s.-e. Chihuahua. - Flowering June to October.

Discussion:

(Plate V)

A highly modified xerophytic shrub adapted to a dune habitat which it shares with mesquite and sometimes with Larrea, like them arresting the drift of blown sand by their tangled branches and forming hummocks. The combination of almost leafless (in summer truly leafless) stems clad in retrorsely subappressed hairs arid speckled with little orange blister-glands with many small headlike racemes of blue (in fma. subrosea purple, in fma. arsenei albino) flowers distinguishes the species from all others. While the reduced foliage recalls Ps. emoryi, the retrorse pubescence points to closer relationship with the inter- montane Ps. thompsonae and Ps. polydenius, which differ collectively in their marcescent petals and stiffly divaricate or zigzag mode of branching. The pliant broomlike stems of Ps. scoparius curiously resemble those of Psoralea juncea Eastw., a denizen of dunes in the Colorado Basin.

According to Kearney and Peebles (1960, p. 436) Ps. scoparius occurs disjunctly on the headwaters of the Little Colorado River in Coconino County, Arizona (near Leupp, Whiting 3321). No corresponding specimens were found in 1970 at US and more direct evidence of this surprising range-extension is required.

Distribution:United States of America North America| Arizona United States of America North America| Texas United States of America North America| Mexico North America| Chihuahua Mexico North America|

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