Psorothamnus thompsonae var. thompsonae

  • Title

    Psorothamnus thompsonae var. thompsonae

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Psorothamnus thompsonae (Vail) S.L.Welsh & N.D.Atwood var. thompsonae

  • Description

    9a. Psorothamnus thompsonae (Vail) Welsh & Atwood var. thompsonae

    (Plate VII)

    Characters as given in key; leaflets never decurrent.— Collections: 13 (iii).

    Hummocked dunes and dunelike or bouldery talus slopes under cliffs, sometimes colonial along sandy and gravelly washes of the canyon floor, confined to red and white sandstones, 1080-1410 m (3600-4700 ft), locally abundant but of highly restricted range in low valleys and canyons leading to the Colorado River in e.-centr. Wayne, e. Garfield, and lower reaches of White Canyon in adjoining San Juan counties, Utah. — Flowering late May to July. — Representative: Utah. Wayne: McVaugh 14,611 (NY); Holmgren et al. 10,944 (UC). Garfield: Barneby 15,021 (CAS, NY); Maguire 10,608, 10,609 (NY, UC); Cronquist 9046 (NY, and widely distributed). San Juan: Barneby 13,083 (CAS, NY), 15,014.

    Psorothamnus thompsonae (Vail) Welsh & Atwood, Great Basin Nat. 35(4): 354. 1975, based on Parosela thompsonae (Ellen Powell Thompson) Vail, Bull. Torrey Club 24: 18. 1897. — "Original locality, Northern Arizona. Type collected by Mrs. Thompson, 1872."—Holotypus, collected probably, like some others gathered by Mrs. Thompson and Capt. Bishop on Powell’s Grand Canyon Expedition, in southeastern Utah, US! isotypus (fragm), NY! — Dalea thompsonae (Vail) L. O. Wms., Ann. Missouri Bot. Gard. 23: 451. 1936; Tidest. in Tidest. & Kitt., Fl. Ariz. & New Mex. 181. 1941.

    This is one of the most colorful small desert shrubs of its region, the low prickly mounds of twigs and foliage disappearing in May beneath a cloud of vivid pink-purple flowers. The whole plant is strongly scented when crushed, the orange or red glands of the stems yielding an aromatic resinous oil. Until recent years Ps. thompsonae was little known, its range lying in a corner of Utah only lately opened to easy access. Rydberg knew the species only from the type, and failed to notice the insertion of all petals on the hypanthium rim, in consequence accepting it as Parosela, despite its generic characters of Psorothamnus. The known range of var. thompsonae extends from a point about ten miles south of Hanks- ville southeast across the east foothills of the Henry Mountains to Hite, there passing to the east bank of the Colorado River in the lower reaches of White Canyon, a total airline distance of less than 40 miles. It may, of course, recur lower down the Colorado, possibly in Arizona, as suggested in the protologue, but this awaits confirmation in the form of specimens.