Psorothamnus arborescens var. pubescens

  • Title

    Psorothamnus arborescens var. pubescens

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Psorothamnus arborescens var. pubescens (Parish) Barneby

  • Description

    4d. Psorothamnus arborescens (Torrey) Barneby var. pubescens (Parish) Barneby

    (Plate IV)

    Habitally similar to var. arborescens, up to 6-8 dm tall, the young branches often purplish, becoming furrowed lengthwise, the foliage loosely strigulose or pilosulous with subappressed or weakly ascending hairs up to 0.2-0.5 mm long, either green or ashen, the calyx usually pilosulous with widely divergent hairs up to 0.5-1 mm long, sometimes loosely strigulose with hairs less than 0.35 mm long; leaves 1.5-3.5 cm long, the leaflets (5) 7-11, linear to linear-oblanceolate, 3-14 mm long, 0.4-1.4 mm wide, the upper 1-3 commonly decurrent, the rest usually jointed but rarely petiolulate; racemes ± 2.5-5 cm long; calyx 7.3-9 mm long, the hypanthium 1.4-2 mm deep, the tube 3.6-4.4 mm long, its orifice symmetrical (all sinuses ± equally deep), the lanceolate teeth subequal in length, 3.5-5.4 mm long, the ventral pair ± twice as wide as the dorsal one, at base 1.2-1.6 mm wide; petals indigo-blue; banner ± 7 mm long, the claw 2 mm, the blade 5-5.2 mm long, 4.4-5.4 mm wide; keel 8.2-9.1 mm long, the claws 3.1-3.7 mm, the blades 6-6.4 mm long, 2.7-3.7 mm wide; pod pilosulous on the sides, usually densely so. — Collections: 8 (i).

    Rocky clay knolls and talus under cliffs, on sandstone, 1035-1470 m (3450-4900 ft), rare and local around the e. end of House Rock Valley of the Colorado River in Coconino County, Arizona, from Lees Ferry (or Navajo Bridge) to points 5 miles s. and 17 miles w., to be sought on benches leading down into Grand Canyon. — Flowering late April to June. —Material: Arizona. Coconino: S. B. Benson 137 (UC); Peebles & Parker 14,648, 14657 (NY, US); Barkley & Reed4360 (NY); Ripley & Barneby 4912 (CAS, NY); Bishop ("Utah, 1872," fragm., perhaps = isotypus of D. amoena, NY).

    Psorothamnus arborescens var. pubescens (loosely hairy compared with Ps. johnsoni) Parish, Bot. Gaz. 55: 308. 1913.— "Lee’s Ferry, Arizona, June 13, 1890, Jones 3076." — Holotypus, DS (hb. Parish.)! isotypi, UC, US! — Psorodendron pubescens (Parish) Rydb., N. Amer. Fl. 24: 44. 1919. Dalea fremontii var. pubescens (Parish) L. Benson, Amer. Jour. Bot. 30: 239. 1943. D. amoena war. pubescens (Parish) Peebles, Jour. Wash. Acad. 30: 473. 1940.

    Dalea amoena (agreable) Wats., Amer. Nat. 7: 300. 1873.— "Northern Arizona (Mrs. E. P. Thompson). In damp places; April." —Holotypus, labelled‘Kanab, 1872’, GH! isotypi (fragm.), NY, US! — Parosela amoena (Wats.) Vail, Bull. Torrey Club 24: 17. 1897. Psorodendron amoenum (Wats.) Rydb., N. Amer. Fl. 24: 44. 1919. Dalea fremontii var. amoena (Wats.) Tidest. in Tidest. & Kitt. Fl. Ariz. & New Mex. 180. 1941, comb, illegit.

    A distinguished endemic of the Colorado River canyonlands, var. pubescens is a truly rare plant, with a known range hardly exceeding 25 kilometers in long diameter, this situated at a distance of some 420 kilometers (or 260 miles) east of its near relatives in the Mohave Desert. Even within this restricted range the variety retains some of the variability in pubescence that characterizes its species as a whole, the hairs on the leaves differing from one plant to the next in density and on the calyx in length, with extremes here of 0.3-1 mm. The type-collection of var. pubescens represents the phase with relatively long calyx-hairs, and was not recognized by Parish as related to the sympatric Dalea amoena. Rydberg maintained these two proposals as a coordinate species of Psorodendron supposedly characterized by elongate calyx-teeth of about equal length. However the teeth are not in reality longer than in some specimens of var. arborescens and the ventral pair are almost twice as wide as the dorsal tooth. The combination of linear leaflets, a symmetrical orifice to the calyx, and a disjunct dispersal are the genuinely distinctive differential characters.

    Nothing exact is known about the type-locality of D. amoena. Vail thought it must be Kanab, Utah, where the Powell Grand Canyon Expedition maintained its headquarters in the summer of 1872, but this is probably a mistake. Several other plants (e.g., Psorothamnus thompsonae, Petalostemon flavescens, Astragalus episcopus Wats.) supposedly collected near Kanab by Ellen Powell Thompson and Captain E. K. Bishop have not been seen since in that vicinity. Bishop certainly, and possibly Mrs. Thompson also, must have accompanied Powell upstream at least as far as Grand River, Utah, and could well have encountered var. pubescens within its range as now known. It seems not unlikely that the fragmentary Bishop collection at NY is really part of the type-collection. It is labelled "Utah", suggesting that var. pubescens, at least before construction of Glen Canyon Dam, followed the Colorado northward across the state line.