74. Astragalus potosinus Barneby, Mem. New York Bot. Gard. 13: 166. 1964 Type:— MEXICO, San Luis Potosí, sine loc, 1878, C. C. Parry & Ed. Palmer 775 (holotype: NY00005832!; isotype: P00585141 digital image!, ISC-v-0000334 digital image!, NA0095603 digital image!, NA0095602 digital image!). Perennial. Stems up to 50 cm long, ascendant, pilose, trichomes up to 0.7 mm long, straight or sinuos, sub-appressed. Stipules 1.5–6 mm long, clasping and connate (the lowest ones), constituting an apical bidentate sheath, the upper ones simple, lanceolate to triangular, constituting a sheath half of its length. Leaves 1.5–6 cm long, leaflets 11–23, 2–16 mm long, oblong, elliptic to obovate, truncate or retuse, adaxially glabrate, scattered and appressed pubescent to densely pubescent, especially when young. Peduncles 3–15 cm long, straight or slightly curved; the racemes 1–7.5 cm long, flowers 8–20. Flowers purple, turning bluish or ochroleucous when drying; the calyx 4–6.1 × 2.2–2.7 mm, pilose, trichomes white or black, sometimes both mixed, the tube 2.3–3.4 mm long, campanulate, the teeth 1.5–3 mm long, subulate; the banner 7.4–8.4 × 3.9–4.6 mm, ovate to oblanceolate, briefly retuse; the wings 7–8.3 × 1.5–2.3 mm, the claw 2.7–3.2 mm long, the blade 5.1–6.1 mm long, oblong to oblanceolate, oblique; the keel 5.8–6.3 × 1.9–2.1 mm, the claw 2.8–3 mm long, the blade 3–4 mm long, oblique-obovate. Pod 14–25 × 4–6 mm, deflexed, stipitate (stipe 2–5 mm long), linear, oblong to elliptic, dorsoventrally compressed, ventrally carinate, dorsally open and slightly sulcate, the valves thin, turning papery with age, ochre or even black with age, minute strigose, trichomes white or black, or both mixed, reticulate; septum incomplete; ovules 10–15; seeds 1.7–2 mm long, mitten shaped, brown, smooth. Distribution:— Endemic to Mexico, central part of Mexico, south San Luis Potosí (around San Luis Potosí City), central and west of Guanajuato, isolated in southwest Durango (El Salto) (Fig. 22). Habitat:— Cold humid plains; north slopes; stony soils; pine-oak forest; oak - manzanita forest; conifer forest; 1829–2591 m. Comments:— In Durango, A. potosinus share similar habitat with A. hartweggi, both species have purple flowers, but A. hartwegii has triquetrous and sessile pod. Astragalus pennellianus (endemic from Durango) is very similar carpologically and sympatric to A. potosinus, but the first one, regularly has white petals (very rarely with purple-light tones), but averaging 25–41 leaflets, and with both, the ovary and the pod pubescent. Further south of the distribution of this species, in San Luis Potosi, Querétaro, and Guanajuato, A. potosinus is associated with at least eight species of Astragalus, but only two of them (A. strigulosus y A. tioides) possess oblong, elliptic, ellipsoid or somewhat widened stipitate pods, never triquetrous or inflated like a bladder. Astragalus strigulosus can easily distinguished of those two by its white petals, and A. tioides is discernible by its few flowered (2–5) racemes, larger petals (banner 11 mm, wings 8.9–9.1 mm, and keel 7.1 mm), slightly larger (20–35 mm) pod, and shorter stipe (1–2 mm long). Specimens examined:— DURANGO: 13 August 1959, 6 miles south-west of El Salto, U. T. Waterfall 15476a (NY); 5 October 1965, 3½ miles west of El Salto, H. D. D. Ripley 13974 (NY). GUANAJUATO: 29 October 1969, Mts. n-e. of Guanajuato, H. D. Ripley 13366, R. C. Barneby (NY); 27 April 1949, 5 millas al O de Cerro Zamorano, R. McVaugh 10399 (MEXU). QUERÉTARO: 24 November 1989, E. González P. 1280 (MEXU). SAN LUIS POTOSÍ: 1879, Ex convalli San Luis Potosí, J. G. Schafner 615/821 (MEXU, NY), 822a (MEXU); 1878, Chiefly in the region of San Luís Potosí. Alt. 6000–8000 ft, C. C. Parry 175, E. Palmer (NY); 6 February1963, Rancho El Milagro, Km 37 carretera San Luis Potosí-Río Verde, Mpio. Zaragoza, A. Gómez 842 (ENCB, MEXU); 6 October 1971, Las Ciénegas, en lo alto de la Sierra San Miguelito, Mpio. Villa de Reyes, M. F. Robert 1187 (ENCB).

Published as part of Castillón, Eduardo Estrada, Quintanilla, José Ángel Villarreal, Delgado-Salinas, Alfonso & Rebman, Jon P., 2023, The genus Astragalus (Leguminosae: Papilionoideae: Galegeae) in Mexico, pp. 1921-1935 in Phytotaxa 586 (1) on pages 1921-1935, DOI: 10.11646/phytotaxa.586.1.1, http://zenodo.org/record/7703999