Astragalus nuttallianus DC., Prodr.

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

62. Astragalus nuttallianus DC., Prodr. [A. P. de Candolle] 2: 289. 1825

Annual, short duration. Stems up to 45 cm long, single at base or several, suberect, erect or ascendant, glabrate, subglabrate, strigose or pilose, the trichomes up to 1.4 mm long, sub-appressed or almost extended. Stipules 1–9 mm long, semi-clasping to totally completely clasping, not connate, triangular, ovate to lanceolate. Leaves 1–8.5 cm long, leaflets 3–23, 2–17 mm long, linear, elliptic, oblong, oblong-elliptic to obovate, truncate, slight to distally deeply retuse, sometimes dimorphic, the lowest ones more wide, adaxially glabrate or pubescent. Peduncles 1–10 cm long, straight or incurved; the racemes up to 3 cm long, lax, rarely subcapitate, flowers 1–27. Flowers white, rose, purple, pale purple, purple-white, sometimes, the banner white colored in the fold, turning blue or violet when drying; the calyx 2.4–5.8 mm long, subglabrate, dense villous or pilose, the tube 1.3–3.2 mm long, the teeth 1–3.2 mm long, lanceolate; the banner 3.5–13 mm long, recurved, suborbicular to obovate, basally cuneate, truncate or slightly retuse; the wings 3.6–10.7 mm long, oblanceolate; the keel 3.7–9.3 mm long, distally semi-obovate, lunate, rounded or triangular. Pod ascending, extended or pendulous, sessile, linear, linear-oblong, oblanceolate, straight slight to evidently curved, triquetrous, laterally somewhat compressed when young, dorsally slightly sulcate or turning flat or somewhat convex with age, the valves thin, papery, glabrate, strigose to villous, green, ochre, brown or black to purple, when ripen, finely reticulate, septum complete, the pod thence bilocular or the septum incomplete or almost absent, persistent, opening when maturing on the peduncle; ovules 2–17; seeds 1.3–2.7 mm long, mitten shape, ochre to olivegreen, frequently with purple spots.

Distribution:— One of the species with the widest distribution in Mexico, inhabiting multiple ecosystems, along almost of the Peninsula of Baja California, except the southern part of Baja California Sur. In the north, from Sonora to Tamaulipas, from there to central Puebla.

Notes:— The most closely related species to A. nuttallianus is A. emoryanus var. emoryanus , both species have multiple morphological characteristics in common. They can be distinguished based on the form of keel apex, pubescence of the calyx teeth, leaflets form in some leaves and time of persistence of the pod in the racemes and the dehiscence, in A. emoryanus the keel apex is rounded or blunt, its leaflets are always blunt, obcordate or retuse, it never has elliptic or subacute leaflets, and the caducous pod opens only after it is on the floor.

A nuttallianus is composed of nine varieties ( Barneby, 1964), some of them sympatric, others isolated and locally distributed, six of them occur in Mexico and are differentiated based on leaflet shape, pubescence, and calyx and teeth sizes as well as the ovary and pods pubescence.

1. Leaflets elliptic to ovate, obtuse to acute, sometimes some of them retuse.......................................................................................2

- Leaflets all retuse or truncate .............................................................................................................................................................5

2. Calyx trichomes appressed o slightlty ascendant, 0.3–0.8 mm long..................................................................................................3

- Calyx trichomes hispidous to ciliate, not appressed, 0.6–1.2 mm long .............................................................................................4

3. Leaflets elliptic, none retuse; calyx tube 1.9–2.8 mm long....................................................................................... var. imperfectus

- Leaflets of basal leaves retuse, the ones of the upper ones elliptic and acute; calyx tube… 1.4–1.7 mm long........ var. cedrosensis

4. Pod hirsute, trichomes up to 1mm long; leaflets 11–13 .......................................................................................... var. trichocarpus

- Pod glabrate or strigose, trichomes 0.5 mm long or shorter; leaflets commonly 7–11................................................. var. austrinus

5. Ovary glabrate ........................................................................................................................................................... var. nutallianus

- Ovary pubescent ........................................................................................................................................................... var. zapatanus