Psorothamnus polydenius (Torr. ex S.Watson) 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

  • Scientific Name

    Psorothamnus polydenius (Torr. ex S.Watson) Rydb.

  • Description

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    Species Description - Stiffly angular, divaricately branching shrubs up to 0.4-1 (1.5) m tall, the stout aged stems leafless, the ultimate twigs becoming subspinose after shedding the terminal flower-racemes, the younger stems densely silky-pilosulous with retrorsely subappressed or narrowly descending lustrous hairs up to 1.5-4 mm long, and densely sprinkled with orange blister-glands (often when dried collapsing and saucer-shaped), the foliage pilosulous with loosely ascending, spreading, or subappressed hairs up to 0.25-0.5 mm long, the ashen leaflets pubescent both sides, rarely thinly so and greenish, charged beneath with 1 subapical and 1-3 pairs of livid submarginal glands; leaf-spurs subobsolete up to 1 mm long; stipules fugacious, triangular or subulate, gland-tipped, 0.4-1 mm long; leaves mostly 7-15, rarely 27 mm long, subsessile or shortly petioled, with 3-6 pairs of obovate, obovate-cuneate, or suborbicular, emarginate or retuse flat or loosely folded leaflets 1-4.5 mm long; peduncles leaf-opposed and terminal to firm tapering branchlets; racemes usually dense but not at all conelike, ovoid to globose or rarely oblong-cylindroid, without petals 10-14 mm diam, the pilosulous axis finally 3-30 mm long; bracts deciduous, lanceolate or lance-attenuate, pilosulous dorsally, tipped with a subcapitate gland; pedicels 0.2-0.7 (0.8) mm long, charged near base and apex with pairs of small orange glands; calyx 3.9-5.3 (8.3) mm long, pilosulous externally from base upward or only on the teeth, the tube (measured to a lateral sinus) 1.9-2.8 (3) mm long, its ribs becoming prominent but remaining slender, the membranous intervals charged with 1 row of 2-4 (the ventral intervals with up to 6, more scattered) glands, the ventral sinus less deeply recessed than the lateral ones and the orifice therefore oblique, the teeth varying from triangular-acuminate to narrowly lance-acuminate or -caudate, the dorsal one longest, either a little shorter or longer than tube, the ventral pair broadest and shortest; petals marcescent, all opening pink- purple, the banner with a golden eye-spot, this and wings gland-tipped, the keel usually glandless; banner 4.6-6.1 (6.6) mm long, the antrorsely arched claw 2-2.5 (2.8) mm, the ovate-cordate, emarginate or retuse blade 3.2-4.2 (4.6) mm long, 2.7-4.6 mm wide; wings 5.4-7 mm long, the claw 1.9-2.5 (2.8) mm, the narrowly oblong, obtuse or truncate-emarginate blade 4-5 (5.4) mm long, 1.5-2.1 mm wide; keel 5.7-8 mm long, the claws (1.9) 2.2-3 mm, the broadly obovate blades (3.7) 4-5.3 mm long, 2.4-3.7 mm wide; androecium 5.2-6.8 mm long, the connective gland-tipped, the anthers (0.55) 0.6-0.8 (1) mm long; ovules 2, collateral; pod ± 2.5 mm long, obliquely clavate-obovoid, the style-base lateral, the valves glabrous and hyaline at base, distally rugulose, thinly pilosulous, gross-glandular; seed (seldom seen) 2-2.2 mm long.

  • Discussion

    (Plates VI, VII)

    A small angularly crooked shrub, the young stems clad in lustrous deflexed hairs and dotted with many red or orange resinous blisters. In the Great Basin and Mohave Desert Ps. polydenius is the only member of the genus characterized by retrorse stem-pubescence. Its disjunct representative on Green River in east-central Utah approaches the range of the related Ps. thompsonae which differs, however, in relative proportions of calyx-teeth and glabrous (not externally pubescent) petals. The small upper branchlets of Ps. polydenius harden into stout but blunt thorns; there are, however, no subterminal inflorescences modified into truly spinose branchlets, a feature of Ps. thompsonae not matched elsewhere in the genus. The main range of Ps. polydenius extends through the basins and desert valleys lying in the rain-shadow of Sierra Nevada from the Humboldt and Carson sinks south into central Mohave Desert, with outlying stations on the Virgin and Meadow Valley affluents of the Colorado in extreme s.-w. Utah and adjoining Nevada. A disjunct population on Green River in e.-centr. Utah, still little known, seems to differ enough to deserve taxonomic recognition.

    The epithet polydenius was originally so spelled by Torrey (in herb., NY) and published by Watson in the same form. The correction to polyadenius, widely adopted in the literature, is to be condemned.