Astragalus nuttallianus
Prodr. 2: 289. 1825.
Plants annual or winter-annual, usually slender, (1–)2–30(–45) cm, strigose, strigulose, pilosulous, or hirsutulous, hairs basifixed; taproot slender. Stems rarely more than 15, erect, ascending, prostrate, or decumbent, glabrate, sparsely strigulose, villosulous, or pilose. Leaves 1–6.5(–9.5) cm; stipules (1–)1.5–6(–9) mm, papery at proximal nodes, herbaceous at distal nodes; leaflets (5 or)7–19(–23), blades linear-elliptic and linear-oblong to obovate, 2–14(–17) mm, apex acute to emarginate, surfaces pubescent abaxially, glabrous or pubescent adaxially. Peduncles erect or incurved-ascending, (0.2–)0.5–9(–10) cm. Racemes (1 or)2–10(–27)-flowered, flowers ascending to declined; axis 0–2(–)3 cm in fruit; bracts 0.5–2.5 mm; bracteoles 0 or 1. Pedicels 0.4–1.6 mm. Flowers 3.7–13 mm; calyx (1.7–)3–5.6(–5.7) mm, strigulose, hirsutulous, or pilose, tube (1–)1.3–3.1 mm, lobes linear-setaceous to narrowly lanceolate, (0.7–)1–3.2 mm; corolla whitish, lilac, or pink-purple; banner recurved through 40–45°; keel 3.7–6.8(–9.3) mm, apex obtusely round to sharply deltate, beaklike or not. Styles glabrous. Legumes ascending, spreading, or declined, green or purple-tinged becoming stramineous or brownish then black, ± straight or incurved through 0.3–0.5 spiral, linear or linear-oblanceoloid, 3-sided compressed, dehiscent on plant, (7–)10–26 × (1.6–)2.1–3.5 mm, usually bilocular, rarely ± unilocular, thin becoming papery, glabrous, strigulose, or villosulous, hairs straight; stipe (0–)0.5–0.9 mm. Seeds 10–22.
Distribution
w United States, n Mexico.
Discussion
Varieties 9 (9 in the flora).
The Astragalus nuttallianus complex is a series of forms found in a wide region of the southwestern and south-central United States and adjacent Mexico. There are two groups discernable: a western phalanx wherein varietal differentiation is apparently ecologically and geographically controlled, and there is intergradation where one form meets another; and the central and eastern Texas group where several varieties are sympatric, but apparently do not form intermediates. Astragalus nuttallianus is often confused with A. emoryanus (see discussion under 316. A. emoryanus).
Selected References
None.
Lower Taxa
Key
| 1 | Leaflet blade apex often retuse or truncate-emarginate, sometimes acute. | > 2 |
| 2 | Herbage hirsutulous; legumes loosely strigulose; banners (4–)4.9–6.7 mm; s Texas. | Astragalus nuttallianus var. zapatanus |
| 2 | Herbage sparsely strigulose or strigose-pilosulous; legumes glabrous; banners (4.3–)4.8–13 mm; Alabama, Arkansas, Kansas, Louisiana, Oklahoma, Texas. | > 3 |
| 3 | Banners (4.3–)4.8–7.3 mm, keel apex triangular-acute or sharply deltate; raceme axis to 0.8(–1) cm in fruit; Oklahoma to sc, e Texas, Kansas, Arkansas, Louisiana, and Alabama. | Astragalus nuttallianus var. nuttallianus |
| 3 | Banners (6.4–)8.5–13 mm, keel apex obtusely rounded; raceme axis to (0.5–)1–3 cm in fruit; c, w Texas. | Astragalus nuttallianus var. macilentus |
| 1 | Leaflet blade apex acute, obtuse, round, retuse, or emarginate, usually not retuse or truncate-emarginate for all leaflets. | > 4 |
| 4 | Keel apex obtusely rounded; raceme axis (0–)0.5–3 cm in fruit; legumes usually glabrous, sometimes minutely strigulose; n Arizona, se Colorado, New Mexico, c, w Texas, and s Utah. | > 5 |
| 5 | Banners 6.3–7.6(–9.2) mm; Four Corners area. | Astragalus nuttallianus var. micranthiformis |
| 5 | Banners (6.4–)8.5–13 mm; c, w Texas. | Astragalus nuttallianus var. macilentus |
| 4 | Keel apex sharply deltate or triangular-acute or -subacute, sometimes beaklike; raceme axis (0–)0.2–1(–2) cm in fruit; legumes glabrous, strigulose, or hirsutulous; Arizona, California, Louisiana, Nevada, New Mexico, Oklahoma, Texas, Utah. | > 6 |
| 6 | Calyces strigulose or hirsutulous, lobes (0.7–)1–1.7(–2) mm; s, c Arizona to Utah, se California, s Nevada. | > 7 |
| 7 | Leaflets monomorphic, blades elliptic throughout; calyx tube 1.9–2.8 mm; e Mojave Desert, California, to Utah and w, c Arizona, s Nevada. | Astragalus nuttallianus var. imperfectus |
| 7 | Leaflets dimorphic, blades of proximal leaves cuneate or obcordate, blades of distal leaves linear-elliptic; calyx tube (1–)1.4–1.7 mm; sw Colorado Desert, California, to s Arizona. | Astragalus nuttallianus var. cedrosensis |
| 6 | Calyces hirsute, hirsutulous, or pilose, lobes 1.8–2.1(–3.1) mm; Arizona, Louisiana, New Mexico, Oklahoma, Texas. | > 8 |
| 8 | Banners 7–9(–9.5) mm; racemes 4–9(–12)-flowered; legumes glabrous; Cameron Parish, Louisiana, e Texas, from Red River to Edwards Plateau and Sabine River. | Astragalus nuttallianus var. pleianthus |
| 8 | Banners (4–)5–7 mm; racemes (1 or)2–6(–8)-flowered; legumes glabrous, strigulose, or hirsutulous; s Kansas to s Texas, westward to s California. | > 9 |
| 9 | Legumes hirsutulous; leaflets 11 or 13; e, s Texas, mostly on Coastal Plain, and w Oklahoma to sw New Mexico. | Astragalus nuttallianus var. trichocarpus |
| 9 | Legumes glabrous or strigulose; leaflets 7–11(–17); s Kansas to s Texas, westward to s California. | Astragalus nuttallianus var. austrinus |