Astragalus didymocarpus Hook. & Arn., Bot. Beechey Voy.

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

19. Astragalus didymocarpus Hook. & Arn., Bot. Beechey Voy. 334, pl. 81. 1840

Annual or perennial but of short duration. Stems up to 45 cm long, erect o decumbent with the stems spreading, branched from base, strigose to canescent, the trichomes up to 0.8 mm long, straight to ascending, appressed. Stipules 0.5–1.5 mm long, triangular, ovate to lanceolate, semi-clasping, not connate. Leaves 1–7.5 cm long, leaflets 9–17, 1–14 mm long, linear, oblong to oblanceolate, retuse, glabrate or slightly pubescent adaxially. Peduncles 1–8 cm long; the racemes 0.5–2.2 cm long, compact, and dense, oblong, cylindrical, ovoid or subglobose, flowers 5–30, ascendant. Flowers white, pale-pink, blue*, blue-purple**, purplish***, purplish-lilac, blue-violet, with lavender to rose-purple tones, occasionally turning bluish when drying; the calyx 3–5.4 × 1.6–3.2 mm, campanulate, ovate o dome shaped (turbinate), dense pubsecent with straight white, black or mix of both trichomes, up to 1 mm long, the tube 1.6–3.2 mm long, the teeth 0.8–2.5 mm long, linear to subulate; the banner 4–9.8 mm long, recurved, spathulate, shallowly retuse; the wings 2.8–7.1 mm long; the keel 3–7.2 mm long. Pod 2–4.2 mm long, ascendant or spread, sessile, inflate, globose to subglobose, laterally compressed, ventrally carinate and dorsally sulcate, inequilateorus, gibous, the valves slightly fleshy, turning hard-papery with age, with scattered or dense pubescense distally only, the trichomes adjacent to the veins, rarely the pod glabrate, greenish, becoming brown with age, occasionally purple speckled, evident reticulate, the veins elevated and prominent, septum complete, the pod thence bilocular or almost so; ovules 2; seeds 1.4–2.7 mm long, ochre, olive, brown to orange.

Distribution:— In Mexico, restricted to Baja California, from Tijuana, Tecate and La Rumorosa spreading south to Sierra Juárez and Sierra San Pedro Mártir to Cataviña; from the west coast, through Rosarito, Ensenada, Vicente Guerrero, San Quintín to El Rosario. Also, distributed in California, Arizona and Nevada ( USA). Three of the infraspecific categories extend their distribution from north California to almost the southern end of Baja California.

Comments:— Three of its four varieties are distributed in Mexico, separated on the basis of petal and calyx teeth size and color of the pubescence. The species is discernible by its annual habit, compact racemes, and small flowers and pods, those always having only 2 seeds.

1. Keel 4.7–7.2 mm long ............................................................................................................................................... var. obispoensis

- Keel 2.4–4.5 mm long ........................................................................................................................................................................2

2. Calyx teeth 1.6–2.4 mm long, or, if shorter, always slightly longer than tube; calyx mainly with white trichomes, rarely the teeth with several black trichomes; stems prostrate ............................................................................................................. var. dispermus

- Calyx teeth shorter than tube, occasionally of the same size, 0.8–1.4 mm long; calyx mainly with black trichomes, rarely the teeth with several spread white trichomes; stems commonly erect ............................................................................... var. didymocarpus