Monographs Details: Astragalus calycosus var. scaposus (A.Gray) M.E.Jones
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

337d. Astragalus calycosus var. scaposus

Cespitose, forming tufts or small clumps, but of more erect and commonly looser growth than var. calycosus; petals pink-purple except for the white wing-tips; banner 10.5-14 mm.; keel 7.5-9 (10) mm. long; wings 9-12 mm. long, the terminal lobes 0.7-2.2 mm. long, the sinus unappendaged; otherwise as described in the key.—Collections: 45 (xi); representative: Cutler 4656 (NY, SMU, WS); A. & R. Nelson 2045 (NY, SMU); Ripley & Barneby 4312, 8404, 12,619 (CAS, RSA); C. F. Baker 409 (POM, bearing an unpublished epithet ("cyanosemius ) attributed to Greene).

Sandy or gravelly hillsides, plains, and mesas, chiefly on sandstone and limestone, forming colonies and locally abundant in juniper or piñon-juniper forest between 4400 and 6200 feet in the drainage of the Colorado, Little Colorado, and San Juan Rivers, from southeastern Nevada across northern Arizona to southwestern Colorado and northwestern New Mexico; in Arizona extending south to the Salt River in Gila County and to the upper Verde River in Yavapai County, in the latter region occurring in mesquite-grassland at about 3300 feet; reported on questionable authority from the Rio Grande Valley in Socorro County, New Mexico (Plank in 1895, NY) and from the Huachuca Mountains in southern Arizona (Wilcox in 1893, NY).—Map No. 154.—April to June.

Astragalus calycosus var. scaposus (Gray) Jones in Zoë 4: 26. 1893, based on A. scaposus (scapose, of the peduncles) Gray in Proc. Amer. Acad. 13: 366. 1878.—"...Mokiak Pass, near the northeastern [properly northwestern] corner of Arizona, Dr. E. Palmer ... "— Holotypus, Palmer 107 in 1877, GH! isotypi, K, NY!—Hamosa scaposa (Gray) Rydb. in Bull. Torr. Club 32 : 659. 1905.

Astragalus candicans (white) Greene in Bull. Calif. Acad. Sci. 1: 156. 1885.—"Northern Arizona, 1883, Dr. H. H. Rusby."—No typus found at CAS, ND, UC, or US, the holotypus probably originally at CAS but lost in the 1906 fire; neotypus, collected in Hell’s Canyon, apparently near Fort Verde, Yavapai County, Arizona, Rusby 580, NY!

If the type-collection were biologically typical of var. scaposus, the variety might be considered endemic to northwestern Arizona, about the headwaters of the Verde River and on the limestone plateaus north and south of the Colorado River just below the Grand Canyon. Only in this comparatively small area does the average plant (and even there not every individual) possess in combination all the extreme characteristics claimed for var. scaposus: leaves with 4-6 pairs of spaced leaflets, tall scapes bearing loose, several-flowered racemes, and calyx-teeth less than 2 mm. long. As we follow var. scaposus eastward across Arizona, we find that the average plant is of lower stature, sometimes as dwarf as typical var. calycosus, but the comparatively many leaflets and short calyx-teeth thought proper to var. scaposus become more constantly associated. Under high desert conditions in the Four Corners country A. calycosus is represented by a form with short calyx-teeth and stiff, more or less erect but quite short scapes and leaves with only 3-5 leaflets. This ambiguous form (cf. Ora Clark 16,223, herb. Univ. New Mex.) might be referred on technical grounds to var. calycosus. Along streams tributary to the Colorado from the north in southwestern Utah and adjoining Nevada, the average plant of the Torrey milk-vetch falls neatly between the ideal concepts of vars. calycosus and scaposus formulated in the key. At the Grand Canyon precisely typical var, calycosus is found along a strip of limestone pavement on both rims but is replaced within the canyon itself (cf. Eastwood 9544, CAS, etc.) by forms variously transient to var. scaposus.

The var. scaposus is ordinarily the handsomest form of the Torrey milk-vetch. It is more conspicuous than var. calycosus not only because of its greater stature and upstanding inflorescence, but because of its more numerous and more brightly colored flowers. On the Peach Springs plateau and sometimes elsewhere the banner and keel are of a vivid magenta-purple which assumes, by contrast with the white wing-tips, a luminous brilliance in the clear desert light.

The doubtful records listed above require verification by new collections. Wilcox is known to have visited Fort Verde as well as Fort Huachuca on his tour of duty in Arizona, and his specimens may have been mislabeled. At least some of Plank’s plants ostensibly collected at Socorro must have come from points distant from the town (e.g., Silene Plankii Mag. & Hitchc.).