Astragalus humistratus A. Gray

Castillón, Eduardo Estrada, Quintanilla, José Ángel Villarreal, Delgado-Salinas, Alfonso & Rebman, Jon P., 2023, The genus Astragalus (Leguminosae: Papilionoideae: Galegeae) in Mexico, Phytotaxa 586 (1), pp. 1921-1935 : 1921-1935

44. Astragalus humistratus A. Gray , Pl. Wright. 2: 43: 1853

Perennial. Stems up to 85 cm long, distally ascendingt, suberect, prostrate or creeping, with radial growth from base, pubescence dolabriform, the trichomes united in middle of two lateral arms, in the form of “t”, the arms of equal or unequal size, dense, cinereous, green, greenish to silvery. Stipules 1.6–13 mm long, clasping and connate, all large and papery, semi-transparent, nearly the size of leaflets, the lowest ones subtruncate or bidentate, the upper ones, longer, triangular to lanceolate, acute, not bidentate. Leaves 1–7.5 cm long, leaflets 5–19, 2–20 mm long, oblong, ovate, elliptic to obovate, obtuse and mucronate, adaxially glabrate or pubescent. Peduncles 1–9.4 cm long, curved, ascending; the racemes 1–14 cm long, flowers 3–30, compact when young, turning lax with age. Flowers whitishgreen, whitish-rose, magenta, purple to purple-magenta, sometimes dark-blue, rose but drying purple; the calyx 4.5–8 mm long, cinereous, the trichomes white, rarely few black trichomes, the tube 2.4–3.8 mm long, campanulate, the teeth 2–4.5 mm long, subulate; the banner 5.9–11.9 mm long, dorsally carinate, retuse; the wings 5.6–10.8 mm oblanceolate to obovate; the keel 5.1–10 mm long, triangular to deltoid. Pod 0.6–2 x 0.2–0.6 cm, ascending, spreading or slightly deflexed, commonly humistrate, semi-ovoid, inflated bladder-like, oblong to elipsoid, basally rounded, dorsally sulcate, distally contracted in a triangular beak, the valves somewhat fleshy when young, leathery or papery with age, strigose or villose, ochre or brown with age, reticulate or almost so, septum absent; seeds 1.7–2.8 mm long, subquadrangulate, mitten shape, brown or black, sublustrous.

Distribution:— In Mexico, recorded from extreme northern Sonora (Sonoita, Santa Cruz, Cananea, Nogales, and Agua Prieta), along the U.S. border, and central-west Chihuahua (Gómez Farías, Babícora and Guerrero).

Comments:— In the region where this species occur, two other Astragalus two other Astragalus species ( A. amphioxys and A. arizonicus ) with dolabriform pubescence are also found. Astragalus arizonicus has linear to oblong triquetrous pod. The petals (banner 16.2–24.5 mm, wings 15.1–22.4 mm, and the keel 13.2–19.6 mm) of A. amphioxys are almost twice as large as those of A. humistratus .

Two of the six recognized varieties are present in northwestern Mexico, and theya are separated on the basis of the leaflets pubescence.

1. Foliage silvery-canescent, leaflets equally pubescent in both faces; in Mexico, Chihuahua and Sonora ............................................ ................................................................................................................................................................ A. humistratus var. sonorae

- Foliage finely pubescent, green, leaflets subglabrate or glabrate adaxially; in Mexico, exclusive from Chihuahua .......................... ......................................................................................................................................................... A. humistratus var. humistratus