Astragalus mollissimus var. Thompsonae

Acaulescent or nearly so, the stems not over 3 cm. long, mostly concealed by imbricated stipules (4) 5-12 (15) mm. long, the herbage densely villous-tomentose, the longest hairs up to 1-1.8 mm. long; leaves (3) 5-17 (20) cm. long, with (15) 19—31 (35) obovate to suborbicular, obtuse or retuse leaflets 3—14 (18) mm. long; peduncles (3) 4—15 (19) cm. long; racemes (7) 12-25-flowered, the axis (1.5) 2-12 cm. long in fruit; calyx 11-12.5 (14.2) mm. long, the tube 7.7-10 (11.2) mm. long, 3.7-4.6 mm. in diameter, the teeth 2-3.5 (4) mm. long; petals pink-purple; banner 18-22 (24.5) mm. long; wings 17.5-21 (24.5) mm. long, the claws 9-11 (12.5) mm., the blades 9.4-11.5 (13) mm. long, 2.2-3.1 mm. wide; keel 15-8.5 (20.5) mm. long, the claws 9-11.5 (12) mm., the blades 6-7.6 mm. long, 2.8-3.6 mm. wide; pod obliquely ovoid, broadest near the base, 11-23 mm. long, 6—11 mm. in diameter, abruptly incurved near the middle through nearly a right angle into a well-defined, deltoid-acuminate, laterally compressed, unilocular beak, the valves densely villous-tomentose, the longest spreading hairs up to (1.2) 1.5-2 mm. long; ovules 28-38 (41).—Collections: 61 (xx); representative: Train 2619 (NA, NY); Jones 5201 (NY, POM); Eastwood & Howell 9281 (CAS, RSA); C. L. Porter 5302 (CAS, NY, TEX); W. A. Weber 3841 (CAS, TEX, WS); J. T• Howell 24,512 (CAS, RSA); Ripley & Barneby 8361 (RSA, UTC).

Dry hillsides, mesas, canyon benches, and gullied slopes at the foot of cliffs and buttes, in sandy or sandy-clay soils derived from shale or sandstone, commonly with junipers, 4650—6750 (in the Grand Canyon descending to 2500) feet, widespread and locally common in the Colorado Basin, from the south foothills (and Flaming Gorge on the north slope) of the Uintah Mountains through eastern Utah to southwestern Colorado and northern Arizona, extending west across the Virgin to the Muddy River in southeastern Nevada, and southeast across the San Juan-Rio Grande Divide to the upper Rio Puerco in northwestern New Mexico, there apparently passing into var. Matthewsii.—Map No. 99.—April to June.

Astragalus mollissimus var. Thompsonae (Wats.), comb. nov., based on A. Thompsonae (Mrs. Ellen P. Thompson, resident at Kanab, Utah, during the summer of 1872 while her brother, Capt. J. W. Powell, was engaged on the survey of the Grand Canyon of the Colorado) Wats. in Proc. Amer. Acad. 10: 344. 1875.—"Collected in Southern Utah on Col. Powell s Expedition, by Mrs. E. P. Thompson and Capt. F. M. Bishop."—Cotypi, mounted together, labeled: "S. Utah, F. M. Bishop, 1873" (fl. & fr.), and "Kanab, Utah, Mrs. E. P. Thompson, 1872" (fr. only), GH! isotypus, Bishop, dated "1872," US!—Tragacantha Thompsonae (Wats.) O. Kze., Rev. Gen. 948. 1891 ("Thomsonae"). Astragalus Bigelovii var. Thompsonae (Wats.) Jones, Contrib. West. Bot. 8: 23. 1898. A syrticolus (dwelling in quicksand) Sheld. in Mum. Bot. Stud. 1: 22. 1894, a superfluous substitute, the supposed obstacle, A. Thomsonianus Bth., being different both in root and form.

Thompson’s woolly locoweed is generally very distinct within its species, and constitutes by itself a third major division of A. mollissimus coordinate with the groups of forms revolving around var. mollissimus and var. Bigelovii. Its pod combines the unilocular beak of the first group with the copious loose vesture of the second, but its individual facies results from a number of small features. Chief among these are the very short or obsolete stems, a calyx proportionately longer and narrower, leaflets on the average smaller and of rounder outline, and pod more strongly inflated and further incurved than in most other forms of the species. Also, the silvery-canescent vesture, unlike that of the other woolly locoweeds which turns rusty a few weeks or a few years after drying, remains permanently unchanged in color. Were it not for the difficulty encountered in separating var. Thompsonae from var. Matthewsii, where their ranges touch in northwestern New Mexico, it would doubtless deserve specific status.

Along the San Juan River from the Four Corners to Aztec and south to the Chaco Canyon, var. Thompsonae is locally abundant and characteristic of its sort, easily distinguished from var. Matthewsii by its more numerous leaflets, longer-pedunculate racemes of more numerous flowers, and pod strongly incurved into a prominent unilocular beak. However, as the traveler passes southeastward across the Continental Divide to the head of the Rio Puerco in Sandoval County, he will encounter puzzling populations in which the differential characters, either severally or together, are blurred or diminished, and individual plants (cf. Ripley & Barneby 8350; Barneby 12,806, RSA) lean now to one and now to the other variety, showing the entities to be confluent in this area.

In favorable seasons var. Thompsonae is a beautiful astragalus, one which is to be expected anywhere on the red or white sandstones of the Colorado Plateau. The individual plant is sometimes greatly reduced in stature during years of scanty spring rainfall, but it starts so early into blossom that a few pods even then will reach maturity, an advantage which is shared by few herbaceous plants of the interior deserts other than some deeply rooting astragali and asclepiads. Normally white-pubescent, the calyx is occasionally villous with fuscous or black hairs which furnish a striking contrast to the silvery foliage and a handsome foil to the purple petals. Such black-hairy forms seem commonest along the foot of the Zion Escarpment in Utah, but occur sporadically in northwestern New Mexico and elsewhere. In the Zion region the calyx is commonly bracteolate.