Astragalus wootonii E. Sheld., Minn. Bot. Stud.

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

101. Astragalus wootonii E. Sheld., Minn. Bot. Stud. 9: 138. 1894

Perennial. Stems up to 50 cm long, several, rarely single, decumbent to prostrate or incurved ascending, rarely erect, strigose to pilose, trichomes up to 0.8 mm long, straight, adpressed or ascending. Stipules 1.5–10.3 mm long, triangular, acuminate, clasping, not connate, embracing a half to three quarters of stem´s circumference. Leaves 1.5–13 cm long, leaflets 7–25, 3.2–21 mm long, linear, oblong, spathulate to obovate, apically obtuse, truncate or notched, sometimes mucronate, adaxially glabrate or almost so. Peduncles 1–7 cm long; the racemes lax, 0.5–5.3 cm long, flowers 2–15. Flowers whitish, sometimes purple, lavender with red-lilac tones; the calyx 4.2–6.5 × 1.8–2.5 mm, strigose, villous, trichomes white or almost all black, the tube 2–3.2 mm long, campanulate or somewhat turbinate, the teeth 2–3.5 mm long, subulate; the banner 4.6–7.5 × 3.1–6.2 mm, obovate to flabellate, recurved; the wings 4–7.4 × 1.1–2.2, the claw 1.4–2.7 mm long, the blade 2.5–5.6 mm long, oblong to obovate, distally oblique-obovate, incurved; the keel 4.1–6.4 × 1.5–2.4 mm, the claw 1.5–2.6 mm long, the blade 2.7–4.3 mm long, distally oblique, obovate and incurved. Pod 1–4.3 × 0.8–2.2 cm, extended, commonly humistrate, subglobose, ovoid, elliptic, oblique, ellipsoid, inflated like a bladder, basally rounded or narrowed, distally contracted in a small almost obsolete beak, almost spherical to slightly openly sulcate along the sutures, both equally convex or the dorsal one slightly more pronounced, the valves green or with purple tones, strigose, villous or glabrate, turning papery, ochre to light-brown with age, shiny, reticulate, septum absent; ovules 10–21; seeds 2–3 mm long, mitten shaped, brown, orange to purple-brown, opaque.

Distribution:— A species widely distributed in Mexico, from central Sonora and northern Chihuahua and Coahuila, through Durango, Zacatecas and San Luis Potosí, to the south, in the western Michoacán, central and western Puebla, to the west-central Veracruz, in close proximity to Puebla. One of the species with the largest distribution in Mexico, especially in semi-arid areas, entering the region of southern Mexico through the Valley of Mexico.

Comments:— At least 25 other species of Astragalus occur within the distribution of this species. Several of these species can be distinguished by their clasping stipules, simple pubescence, pink, purple or white, or when white, then purple, lavender or red-lilac tinted petals, and widened or inflated bladdery pods ( A. allochrous , A. lentiginosus var. borreganus , A. mollissimus var. earlei , A. m. var. irolanus , A. wootonii var. candollianus and A. w. var. wootonii ). Astragalus mollissimus (both varities) is distinguished by its calyx, the longestin any of these in this group (8.5–13 mm long); A. wootonii is distinguished from the others by its small petals (never larger than 7.5 mm long). In Sonora and Chihuahua, where A. w. var. wootonii and A. allochrous converge, they might be confused because sometimes the A. allochrous flowers may be small (banner 7.2–9.4 mm, wings 6.6–8.8 mm, the keel 6.2–7.5 mm) similar to the largest flowers of A. wootonii . However, they can be distinguished by the shape of the pod, since A. allochrous is oblique, semi-ovoid, its ventral suture is straight to slightly concave, less convex than the dorsal one and with a long developed beak that is easily distinguished from the body, and coupled with its pink to purple-red flowers (turning violet when drying).

Two varieties of A. wootonii are recognized, based on the type of pubescence and number of flowers per raceme ( Barneby, 1964).

1. Pubescence of stems and leaves appressed, trichomes straight, 0.4–0.7 mm long; flowers 3–15 per raceme; Aguascalientes, Chihuahua, Sonora, Durango, Hidalgo, San Luis Potosí and Zacatecas ........................................................................ var. wootonii

- Pubescence of stems and leaves villous to pilose, trichomes extended and incurved-ascending, 0.6–0.8 mm long; flowers 2–5 per raceme; Zacatecas, San Luis Potosí, Guanajuato, Hidalgo, State of Mexico, Puebla, and Veracruz ...................... var. candollianus