Astragalus tioides (Rydb.) Barneby, Mem.

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

96. Astragalus tioides (Rydb.) Barneby, Mem. New York Bot. Gard. 13: 171. 1964

Type: — MEXICO, San Luis Potosí, Valley of San Luis Potosi, 1876, Schaffner 822 (holotype (based on Athelophragma tioides ):

GH00059443 digital image!; isotype (Schaffner 617 & 822): P00585179 digital image!, PH 00005762 digital image!). Atelophragma tioides Rydb., Bull. Torrey Bot. Club 55: 157. 1928.

Perennial. Stems up to 50 cm long, decumbent or almost ascendant, strigose to pilose, trichomes rigid up to 0.8 mm long, mostly appressed with some longer and ascendant ones. Stipules 2–6 mm long, clasping and connate, bidentate, the upper ones slightly longer and simple. Leaves 3–8 cm long, leaflets 7–21, 2.5–12 mm long, oblong to obovate, entire or notched apically, bicolored, abaxially clearer and glabrate. Peduncles 3.5–10 cm long; the racemes short, 0.4–3 cm long, flowers few, 2–5. Flowers purple; the calyx 5.3–6 × 2–2.7 mm, pilose, con trichomes white and black, the tube 3–3.3 mm long, campanulate, the teeth 2.2–2.7 mm long, subulate; banner 11 × 5–6 mm, obovate, basally narrowed, recurved; the wings 8.8–9.1 × 1.9–2.1 mm, the claw 3.6–3.9 mm long, the blade 6.2–6.5 mm long, apically oblique, straight or almost so; the keel 7–7.1 × 1.9–2.2 mm, the claw 3.8–4.1 mm long, the blade 3.3–3.9 mm long, distally oblique, thence almost obovate, and incurved. Pod 20–35 × 3–6.3 mm, deflexed, stipitate (stipe 1–2 mm long), linear to oblong, straight o somewhat curved, narrowed in both ends, dorsoventrally compressed, ventrally carinate, dorsally wide and openly sulcate, the valves somewhat fleshy, glabrate, turning papery-rigid, ochre to black with age, reticulate, septum almost complete; ovules 18–22; seeds 2.6– 2.6 mm long, mitten shaped, brown, smooth.

Distribution:— Endemic to Mexico, southwestern San Luis Potosí (San Luis Potosí City). This species is very rare and has few specimen collections. We do not know the conservation status of this species, however, a good part of the collections come near the city of San Luis Potosí, where the last recorded collection was made in 1954 on the road from San Luis Potosí to Tampico. Perhaps this path is the last route to find this rare species. Since the areas where it was recorded in the 19th and 20th centuries were in areas near San Luis Potosí, today these localities may no longer exist in their natural landscape ( Fig. 26 ).

Habitat:— No specific locality registered.

Comments:— The region that includes the City of San Luis Potosí and surrounding areas, contains at least 11 species of Astragalus . Only three of them have linear, elliptic, oblong, never triquetrous pods, A. potosinus , A. strigulosus and A. tioides . Astragalus strigulosus can be distinguished by its ochroleucous flowers, never purple as in A. tioides and A. potosinus . Both of these species are easily distinguished, since the latter has racemes with 8–20 flowers, and smaller petals (standard 7.4–8.4 mm, wings 7.1–8.3 mm, and keel 5.8–6.3 mm).

Specimens examined:—SAN LUIS POTOSÍ: 1878, Chiefly in the region of San Luis Potosi, C. C. Parry 176, E. Palmer (NY); 1879, San Luis Potosí, J. G. Schaffner 612 (NY, US); non date, San Luis Potosi, Schaffner 822 (MEXU); En route from San Luis Potosi to Tampico (Tamaulipas), Palmer 176 ( US).

Figures

FIGURE 26. Map showing the distribution of Astragalus strigulosus, A. tephrodes, A. thurberi, A. tijuanensis, and A. tioides in Mexico.