Astragalus micranthus Desv., J. Bot. Agric.

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

58. Astragalus micranthus Desv., J. Bot. Agric. 3: 78. 1814

Perennial. Stems up to 50 cm long, prostrate, creeping or distally ascending, basally single or branched, with minute and strigose pubescence, the trichomes up to 0.6 mm long, appressed or slighlty ascending. Stipules 2–7 mm long, the lowest ones amplexicual and connate, the upper ones somewhat clasping to free, lanceolate to ovate. Leaves 2–11 cm long, leaflets 17–31, 2–20 mm long, linear, oblong, ovate, elliptic, occasionally truncate or notched apically, the leaflets similar or diminishing in size distally, adaxially glabrate or almost so. Peduncles 2–15 cm long, straight o incurved; the racemes 3–16 cm long, oblong, flowers 25–80, sometimes but rarely as much as 100, deflexed since young. Flowers purple, yellow, sometimes pale yellow, becoming ochroleucous, yellow-greenish or brown where it folds and distally yellowish when drying; the calyx 2.5–5.6 × 1.3–2.8 mm, villous to strigose, trichomes mainly black, the tube 1.4–3.3 mm long, campanulate, basally oblique, the teeth 0.5–2.6 mm long, triangular to subulate; the banner 4.4–7 × 3–6 mm, recurved, spathulate to fan-shaped, slightly retuse; the wings 4.4–7.9 × 1.2–2.1 mm, the claw 1.8–3.5 mm long, the blade 2.6–5.1 mm long, oblong to oblanceolate; the keel 3.7–7 × 1.8–2.4 mm, the claw 1.8–3.6 mm long, the blade 2.4–4.3 mm long, semi-obovate, incurved. Pod deflexed, stipitate, (stipe minute to 0.5 mm long or smaller, and the pod apparently sessile), the body lanceolate, oblong to elliptic, 5.4–13 × 2.2–3.5 mm, straight o strongly curved, triquetrous, basally obtuse, distally ending in a triangular beak, ventrally keeled, dorsally widely sulcate, the valves thin, papery, greenish to ochre, turning brow-black to black with age, commonly with black trichomes, sometimes some white trichomes present, imperceptibly reticulate, septum incomplete; seeds 1.5–1.6 mm long, mitten shaped, brown o with purple tints.

Distribution:— Central región of Mexico, State of Mexico, Mexico City, Hidalgo, Puebla, Morelos, south to isolated localities in Oaxaca. In northern Mexico recorded only in southeastern San Luis Potosí.

Comments:— From the nine species found in this area, only two species, with simple trichomes and triquetrous pods are found, A. micranthus and A. esperanzae , the last one with longer flowers (banner 7.4–9.4; wings 7.6–9.6 mm, keel 5.7–7.7 mm) and longer pods (12–18 mm long).

Two varities recognized, based on petals and pod size, as well as number and size of flowers. Stems and racemes size are quite heterogeneous to use them as identification character.

1. Racemes 1–3.5 cm long in fruit, with 15–30 flowers; calyx 2.5–3.1 mm long, the teeth 0.6–1.1 mm long; banner 4.5–5.2 mm long; pod 5.5–8 mm long; Estado de Mexico, Hidalgo, Puebla and Veracruz .......................................................................... var. seatoni

- Racemes 3–16 cm long in fruit, with 30–60 flowers; calyx 3.8–5.6 mm long, the teeth 1.1–2.6 mm long; banner 4.5–7 mm long; pod 8.5–13 mm long; State of Mexico, Mexico City, Guanajuato, Hidalgo, Michoacán, Morelos, Oaxaca; Puebla, San Luis Potosí ......................................................................................................................................................................... var. micranthus