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rio fronteras milkvetch, smallflower milkvetch, southern small flower milk vetch

Habit Plants strigulose or hirsutulous. Herbs annual, biennial, or perennial, caulescent; caudex superficial.
Stems

(1–)3–25(–35) cm.

single or few to many.

Leaves

1–6.5 cm;

leaflets 7–11(–17), blades often narrowly elliptic, sometimes broader proximally, apex rounded.

odd-pinnate, petiolate to subsessile;

leaflets (3 or)5–25(or 27).

Racemes

(1–)2–5(–8)-flowered;

axis very short in fruit.

subumbellate or loosely flowered, flowers ascending, spreading, or declined.

Peduncles

3–10 cm.

Flowers

calyx 3.7–5.4 mm, silvery-pilose, tube (1.5–)2–3 mm, lobes 1.8–2.1 mm;

corolla white or tipped pink or purple, banner (4–)5.5–7 mm;

keel apex triangular-acute or sharply deltate, usually beaklike.

Corollas

usually pink-purple, purple or purple-tinged or -tipped, ochroleucous, or lilac, rarely whitish, banner recurved through 20–80°, keel apex acute, round, deltate, or triangular-acuminate, sometimes slightly beaklike.

Calyx

tubes campanulate.

Legumes

13–24 × 1.8–2.8(–3) mm, glabrous or strigulose.

deciduous, usually sessile, rarely short-stipitate, short gynophore sometimes present, ascending, spreading to declined, incurved-ascending, or pendulous, mostly linear to linear-oblanceoloid, oblong, or crescentic, sometimes 3-sided, rarely ellipsoid or fleshy, straight or incurved, rarely slightly decurved, compressed laterally, slightly 3-sided or subterete, bilocular.

Seeds

14–18.

(2–)4–30.

Hairs

basifixed or malpighian.

Stipules

distinct.

2n

= 24.

Astragalus nuttallianus var. austrinus

Astragalus sect. Leptocarpi

Phenology Flowering Mar–May (summer–fall).
Habitat On limestone substrates, in various vegetative types.
Elevation 600–2200 m. (2000–7200 ft.)
Distribution
from FNA
AZ; CA; CO; KS; NM; OK; TX; Mexico (Baja California, Chihuahua, Coahuila, Durango, Nuevo León, Puebla, Sonora)
[BONAP county map]
w United States; se United States; n Mexico
Discussion

Variety austrinus occurs from southern Kansas to the southern tip of Texas and northern Mexico, and westward to Arizona and southern California, where it grades into var. imperfectus (D. Isely 1998).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species 24 (18 in the flora).

Section Leptocarpi is complex morphologically, with eight subsections recognized, one of them, subsect. Coahuilani Barneby, occurring only in northern Mexico. The subsections within the flora area are: subsect. Pringleani Barneby (Astragalus nothoxys); subsect. Arizonici Barneby (A. arizonicus); subsect. Mohavenses Barneby (A. albens, A. mohavensis); subsect. Parvi Barneby (A. hypoxylus); subsect. Tricarinati (Rydberg) Barneby (A. bernardinus, A. tricarinatus); subsect. Californici (A. Gray) Barneby (A. acutirostris, A. breweri, A. claranus, A. emoryanus, A. pauperculus, A. rattanii, A. tener); and subsect. Leptocarpi (M. E. Jones) Barneby (A. leptocarpus, A. lindheimeri, A. nuttallianus, A. nyensis).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 11. FNA vol. 11.
Parent taxa Fabaceae > subfam. Faboideae > Astragalus > sect. Leptocarpi > Astragalus nuttallianus Fabaceae > subfam. Faboideae > Astragalus
Sibling taxa
A. nuttallianus var. cedrosensis, A. nuttallianus var. imperfectus, A. nuttallianus var. macilentus, A. nuttallianus var. micranthiformis, A. nuttallianus var. nuttallianus, A. nuttallianus var. pleianthus, A. nuttallianus var. trichocarpus, A. nuttallianus var. zapatanus
Subordinate taxa
Synonyms Hamosa austrina, A. austrinus
Name authority (Small) Barneby in F. Shreve and I. L. Wiggins: Veg. Fl. Sonoran Desert, 709. (1964) M. E. Jones: Rev. N.-Amer. Astragalus, 266. (1923)
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