Resembling var. Paysoni in appearance, the stems decumbent and ascending, 5-30 cm. long, or sometimes short and closely tufted at anthesis, elongating only as the fruit ripens; herbage pallid or yellowish-green, strigulose, the hairs up to 0.3-0.6 mm. long, the leaflets glabrous above, the inflorescence strigulose or pilosulous with black or mixed black and white hairs of about the same length; leaves (4) 5-15 cm. long, with (13) 17-31 (33) broadly to narrowly elliptic, oval, oblong-oblanceolate, or (in some lower leaves) obovate, obtuse or subacute, sometimes callous-mucronulate leaflets (2) 4—17 mm. long; peduncles 2—9 (11) cm. long; racemes 10-23(30)-flowered, the axis (1) 1.5-7 (9) cm. long in fruit; pedicels 2—4 mm. long in fruit; calyx (8.6) 9.6—12.6 mm. long, the tube (6.3) 7.5-9.2 mm. long, 3.8-4.5 mm. in diameter, the teeth (1.9) 2.3-3.6 mm. long; petals whitish, the keel-tip and sometimes the base of the wing-blades, rarely also the base of the banner, faintly lilac-tinged; banner 17-25 mm. long, (8.2) 9-14 mm. wide; wings 14.4-20.3 mm. long, the claws (6.6) 7-10.4 mm., the blades 8.7-12.7 mm. long, 2.6-3.8 mm. wide; keel (12.8) 13.2-17.3 mm. long, the claws (6.7) 7-11 mm., the blades (6.7) 7-8.5 mm. long, 3.2-3.8 mm. wide; anthers (0.65) 0.7-0.9 mm. long; pod broadly and plumply oblong- ovoid, -obovoid, or subglobose, 1.5-3.5 (4) cm. long, 1.2-2.5 cm. in diameter, the valve-walls 1.2-2 mm. thick, the septum 0.8-2 cm. wide; ovules 38-51, averaging ± 44.—Collections: 11 (v); representative: Ferris 1232 (CAS); Barneby 12,811 (CAS, NY, POM, RSA, US), 12,896 (CAS, NY, RSA), 12,978 (CAS, RSA); Wooton (from Horse Spring) in 1892 (NMC).
Arid sandy plains, dry stony meadows, gravelly banks, and canyon benches, on granitic and various alluvial soils, mostly in grassland or juniper-piñon forest between 5800 and 7600 feet, descending to the floor of the Rio Grande Valley where associated with Larrea at 4900 feet, locally plentiful in scattered stations from the Pecos-Rio Grande Divide in central and southcentral New Mexico west to the north slope of the White Mountains and plains adjacent to the north in eastcentral Arizona.—Map No. 101.—May to July, the fruit ripe in late summer and fall.
Astragalus crassicarpus var. cavus (hollow, of the pod), var. nov., legumine inflate, cavo, nec seminibus filamentisque farcto solido, valvulis 0.8-2 mm. tantum crassis insignis, caeterius var. Paysoni persimilis.—New Mexico: steep gravelly hillside among junipers, 6450 ft., 3 miles e. of Mayhill, in the Sacramento Mountains, Otero County, May 18, 1953, Barneby 11,158.—Holotypus, CAS! isotypi, NY, RSA, US!
The hollow ground-plum, var. cavus, has already been mentioned as an unnamed form (cf. Barneby, 19561, p. 498). It was probably first collected in 1892 by E. O. Wooton in westcentral New Mexico, but I have only recently acquired sufficiently ample material to demonstrate the consistency of the fruiting characters over an extensive area lying well to the south of var. Paysoni. The var. cavus is native to a region where the spring months are extremely dry, but it has retained the early-flowering habit of the other ground-plums and consequently is subjected to most unfavorable conditions at anthesis. As might be expected, flowering specimens are often of dwarf stature, the lower peduncles sometimes appearing subradical, but the stems elongate after the fruit is set and sometimes reach a length of 3 dm. as early as mid-May. The cited collections show great variation in stature which ranges from the tall, robust type- series with very large pods obtained in the mountains during a relatively moist season to the low, tufted, small-fruiting plants obtained in the open plains in Torrance County, New Mexico, (Barneby 12,811, especially) in the exceptionally dry spring of 1955. Both tall and dwarf plants have been collected in different years along the road between Eagar and Nutrioso in Apache County, Arizona. Apart from variation in size, the pods are alike in their relatively thin-textured valves enclosing a large, inflated cavity. In other respects the plants agree closely with var. Paysoni, of which var. cavus is probably a direct derivative adapted to a more arid climate.