Astragalus purshii |
Astragalus tetrapterus |
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Pursh's milkvetch, woollypod milkvetch |
four-wing milkvetch |
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Habit | Plants perennial, acaulescent to shortly caulescent, densely villous to villous-tomentose, hairs basifixed. | Plants perennial, caulescent, strigillose, hairs basifixed. |
Stems | prostrate, loosely to densely tufted, 0–20 cm. |
several, ascending to erect, becoming decumbent in fruit, 10–35(45) cm. |
Leaves | 1–12(17) cm; leaflets (3)5–17(21), elliptic to oblanceolate, 2–14(20) × 1–7 mm; tips obtuse to acute; surfaces densely villous; stipules 2.5–15 mm; free. |
1.5–9 cm; leaflets 9–23, linear, narrowly oblong or elliptic, 1–33 × 0.3–3.2 mm; tips obtuse to acute; surfaces glabrous to strigose; terminal leaflets confluent with rachis in the uppermost leaves; stipules 2–5.5 mm; free. |
Inflorescences | racemes or subumbels, 1–12-flowered; peduncles 1–14 cm; bracts 4–9 mm; pedicels 2–4.3 mm; bracteoles 0–2. |
racemes 6–15-flowered; peduncles 1–6.5 cm; bracts 1.5–3.5 mm; pedicels 1.4–4.3 mm; bracteoles 0–2. |
Flowers | ascending at anthesis; calyces 5.5–16(19) mm, often purple, villous-pilose with white or mixed white and black hairs; tubes 8.5–12.5 mm; teeth subulate, 2.2–6 mm; corollas 19–27 mm; whitish to ochroleucous or pink-purple; ovules 14–40(46). |
ascending at anthesis; calyces (4)5.5–8.7 mm, strigose with black or mixture of black and white hairs; tubes 3.5–7 mm; teeth subulate or triangular, 0.5–2.8 mm; corollas 15–19 mm, white to yellowish and pink or bright pink-purple-tinged; keel faintly to darkly purple-tipped; ovules 28–42. |
Fruits | unilocular, ascending, obliquely ovoid, usually curved, obcompressed, scarcely to deeply sulcate; (7)13–27(30) × 3.5–11 mm, densely white to tawny tomentose or densely villous; hairs nearly always concealing valve surfaces; valves coriaceous, sessile or on gynophores 0–1.6 mm. |
unilocular, declined or pendulous, obliquely oblong or clavate-oblong, curved or coiled, strongly carinate, obcompressed early, becoming sharply tetragonal and 4-winged; wings up to 2.5 mm wide at maturity; (16)20–40 × (4)6–10 mm, glabrous to strigose; valves stiffly papery to subcoriaceous; stipes 0. |
2n | =22. |
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Astragalus purshii |
Astragalus tetrapterus |
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Distribution | ||
Discussion | Western North America. ~8 varieties; 4 varieties treated in Flora. Throughout western North America, particularly in the Intermountain Region, this is a low, tufted milkvetch with white or gray villous hairs and pods resembling balls of cotton. Barneby (1964) stated, “Attempts to devise a practical key to the varieties of A. purshii are never wholly successful.” Variety ophiogenes, the Snake River milkvetch, a native of Idaho, has been reported from Malheur County, but this is apparently based on misidentifications of A. purshii var. lagopinus. Variety ophiogenes has 3–11-flowered racemes and 9–17 leaflets. |
Hillsides of ash-clay-tuff, sandy soils, sagebrush. Flowering May–Jun. 900–1700 m. BR, ECas, Owy. ID, NV; southeast to AZ. Native. The four-winged fruits of this species are unique among Oregon milkvetches. |
Source | Flora of Oregon, volume 2, page 671 Richard Halse |
Flora of Oregon, volume 2, page 675 Richard Halse |
Sibling taxa | ||
Subordinate taxa | ||
Synonyms | Astragalus purshii var. ophiogenes | Astragalus cinerascens, Astragalus tetrapterus var. cinerascens, Astragalus tetrapterus var. tetrapterus |
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