94. Astragalus thurberi A. Gray, Pl. Nov. Thurb. 312. 1854

Type: — MEXICO, Sonora, “ Near Fronteras, & c. Sonora, in dry places; June 1851, Thurber 372 (holotype: GH00059442 digital image!; isotype: NY00005853 digital image!, K000999394 digital image!, MO-128311 digital image!, GH00058968 digital image!, NY01268419 digital image!).

Tragacantha thurberi (A. Gray) Kuntze, Revis. Gen. Pl. 2: 948. 1891. — Phaca thurberi (A. Gray) Kearney, Trans. New York Acad. Sci. 14: 34. 1894.

Perennial but of short duration. Stems up to 45 cm long, decumbent and ascending, strigose, trichomes short, up to 0.5 mm long, sub-apressed or straight. Stipules 2–8 mm long, free, deltoid to triangular, somewhat decurrent basally, not connate. Leaves 2–11.5 cm long, leaflets 7–21, 5–18 mm long, linear, oblong, elliptic, to oblanceolate, adaxially truncate o somewhat notched and mucronate. Peduncles hard, 3–9 cm long; the racemes 2–11 cm long, dense, flowers 7–32. Flowers purple, red-purple, red-lilac, rarely white-yellowish; the calyx 3.3–5 × 1.7–2.5 mm, strigose, trichomes white, sometimes few black ones present, the tube 2.2–3 mm long, campanulate, the teeth 1–2.3 mm long, subulate, one pair longer than rest; the banner 5.7–7.1 × 4.2–6 mm, recurved, ovate to suborbicular, basally narrowed, apically slightly retuse; the wings 5.1–6.7 × 1.6–2.4 mm, the claw 1.8–2.5 mm, the blade 3.6–5 mm long, oblong to obovate, distally oblique, incurved; the keel 4.7–5.6 × 1.7–2 mm, the claw 2–2.9 mm long, the blade 2.6–3.4 mm long, apically oblique, somewhat obovate. Pod, when mature, compact in the infrutescence, spike-shaped, oblong-head or even cylindrical, extended or deflexed, sessile, 6–14 × 6–10 mm, inflated like a bladder, basally rounded, distally contracted in a very short beak, sulcate or not so along sutures, the valves green or sometimes with purple tones, strigose, turning papery and ochre with age, reticulate; septum absent; ovules 8–11; seeds 1.7–2.5 mm long, mitten shaped, golden, brown or ochre, smooth, opaque.

Distribution:— In Mexico, recorded only in the northwestern portion, in northern Sonora (from Nogales, north Cananea, Naco to Agua Prieta) and Chihuahua (San Luis, El Valle, El Berrendo to Las Palmas, 31°18’N – 108°18’W), in close proximity to New Mexico and Arizona (USA). Also, in New Mexico and Arizona (USA) (Fig. 26).

Habitat:— Rocky hills; volcanic and sandy soils; arid plains; sandy streams; grasslands; disturbed areas, desert scrubs with juniper, prickly-pear, acacia, mesquite, Joshua tree, grasses; disturbed areas with juniper - mesquite; natural grassland with mesquite, Joshua tree, prickle pear; desert grassland; 1166–1402 m.

Comments:— The Mexican geopolitical border between Chihuahua and Sonora along the USA border (New Mexico and Arizona) acontain several species with inflated pods, including A. allochrous, A. mollissimus, A. thurberi, and A. wootonii var. wootonii. Both, Astragalus thurberi and A. wootonii have small flowers (banner averaging 4.6–7.5 mm long, wings 4.1–7.5 mm long, and keel 4.1–6.4 mm long)but they can be differentiated easily by the pod size, which is much longer and wider in A. wootonii (averaging 14–42 mm long, 11–18 mm wide).

Specimens examined:—CHIHUAHUA: 20 March 1984, Rolling hills 0.4 miles east of Highway 2 at a point 5.2 road miles northwest of Arroyo Salto de Ojo and 14.3 miles northwest of Janos, A. C. Sanders 4726, W. Charlton, McIntosh, VanWay, Gibeaut, Gould (NY). SONORA: 19 March 1984, Agua Prieta. Along Highway 2, ca. 26 miles east of Agua Prieta and ca. 24 miles west of the state line at Puerto San Luis, A. C. Sanders 4707, W. Charlton, V. Way, McIntosh, Gibeaut, Gould (CAS, JEPS, SD); 20 March 1984, Rolling hills 0.4 miles east of Highway 2 at a point 5.2 road miles northwest of Arroyo Salto de Ojo and 14.3 miles northwest of Janos, A. C. Sanders 4726, W. Charlton, V. Way, McIntosh, Gibeaut, Gould (NY); 1963, 7.9 miles north of Esqueda, I. L. Wiggins 11780 (CAS, US); VI-1851, Dry plains, near Fronteras, G. Thurber 372 (NY); 16 May 2010, Rancho Puerta Blanca, Cuenca Los Ojos, Foundation property, 40.7 km by air E of Agua Prieta, A. L. Reina G., 2010-425, T. Van Devender (USON); 12 April 2003, 4 km SE of Ezqueda, on road to Agua Caliente, A. L. Reina G. 2003-500, T. R. Van Devender (USON); 30 April 2006, 33.7 km E of Agua Prieta on Mex. 2, Rancho Guadalupe, A. L. Reina G. 2007-491, T. R. Van Devender (USON); 10 April 2003, Fronteras — Esqueda A.L. Reina G. 2003-414, T.R. Van Devender, G. Anderson (MEXU); Rancho El Aribabi, Cordón de Las Pilas, a 4.5 km línea recta al SE de la casa del rancho, a 22.4 km al ESE de Imuris, Mpio. Imuris, 2010- 005 A. K. Enriquez et al. (USON).