Astragalus oreganus

  • Title

    Astragalus oreganus

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus oreganus Nutt. ex Torr. & A.Gray

  • Description

    189.  Astragalus oreganus

    Low, rather stout and leafy, with an initial taproot and creeping, cordlike rhizomes, densely strigulose, strigose, or subvillosulous with flattened, straight and appressed, or somewhat twisted and loosely ascending hairs up to 0.6-1.2 mm. long, the stems and herbage pallid green beneath the ashen vesture, the leaflets somewhat bicolored, yellowish-green and sometimes less densely pubescent above; stems arising singly or few together from buds on the horizontal or obliquely ascending rhizomes, 6—20 cm. long, naked, simple, slender and subterranean for a space of 3—10 (14) cm., upon emergence stouter, decumbent with ascending tips, branched or spurred at nearly all nodes below the first peduncle, the internodes all short, not over 3 cm. long and mostly shorter, becoming stiffly flexuous or abruptly zigzag distally; stipules papery, pallid or early becoming so, (2.5) 3.5-11 mm. long, amplexicaul and connate through at least half, the lowest through more than half their length into a loose, bidentate sheath; leaves divaricate or ascending, (2.5) 5-15 cm. long, shortly petioled, with (7) 9-15 (reportedly 21) broadly obovate or suborbicular-obcordate, obtuse or widely and shallowly notched, flat leaflets 4-20 mm. long, these usually diminishing upward along the rachis; peduncles erect or divaricate from the stem, vertical to the ground, 1.5-5.5 cm. long, much shorter than the leaf; racemes rather densely (15) 20-35-flowered, at full anthesis shortly oblong-cylindric, sometimes interrupted at base, the flowers nodding, the axis somewhat elongating, 3-7.5 cm. long in fruit; bracts scarious, ovate, lance-elliptic, or oblanceolate, 2-5.5 mm. long; pedicels ascending or a little arched outward, at anthesis 0.6-1.3 mm., in fruit thickened, 1.2-2.2 mm. long, persistent or sometimes very tardily disjointing under pressure; bracteoles linear-setaceous, up to 1.5 mm. long, attached at or below base of calyx; calyx 6.5-10 mm. long, thinly strigulose with white and often some fuscous hairs, the oblique disc 0.8-1.6 (2) mm. deep, the deeply campanulate or subcylindric tube obliquely truncate or dorsally subgibbous at base, 5.5-7.3 mm. long, 3.2-4.8 mm. in diameter, the subulate teeth 1-3 mm. long, the whole pallid, becoming papery, ruptured, marcescent; petals ochroleucous, concolorous, subpersistent; banner recurved through 50-90°, 15.5-19 mm. long, the cuneate claw expanded into an oblong or ovate-oblong, deeply notched blade 7.5-9 mm. wide; wings 13.2-17.6 mm. long, the claws 5.3-7.2 mm., the narrowly oblong or oblanceolate, truncate or retuse, nearly straight blades 8.4-12.4 mm. long, 2.7-3.1 mm. wide; keel 11.513.5 mm. long, the claws 5.4-6.7 mm., the lunate or lunately elliptic blades 6-7.2 mm. long, 2.9-3.2 mm. wide, incurved through 50-80 (90)° to the bluntly triangular apex; anthers 0.6-0.8 mm. long; pod erect or ascending at a narrow angle, sessile, persistent, oblong in profile, nearly straight or incurved through up to ¼-circle, 1—1.5 (1.8) cm. long, (3) 4—6 mm. in diameter, rounded or subtruncate at base, abruptly contracted at apex into a shortly triangular-acuminate, erect or slightly declined, rigidly cuspidate beak, a trifle obcompressed, bluntly keeled ventrally by the thick, prominent suture, openly and shallowly grooved dorsally, the fleshy, green, thinly strigulose valves becoming brown and leathery, almost smooth or transversely rugulose-reticulate, inflexed below the unilocular beak as a complete septum; ovules (17) 20-28; seeds not seen ripe.—Collections: 17 (v); representative: A. Nelson 7051 (GH, K, MO, NY, RM); C. L. Porter 4242 (NY, RM, SMU, TEX); Ripley & Barneby 7980 (CAS, NY, RSA, UTC), 7999 (CAS, RSA); W. E. Booth 54,560 (RSA).

    Barren bluffs, gullied knolls, dunes, and detritus under cliffs or buttes, in sandy or sandy clay soils derived from weathered sandstone, sometimes on alkaline clay flats moist in spring, 3800-6800 feet, locally abundant along the upper Big Horn and Wind Rivers, from a point a few miles below Dubois, Fremont County, Wyoming, downstream just into southern Carbon County, Montana, and south just across the Continental Divide to the edge of the Red Desert in Sweetwater County, Wyoming,—Map No. 75.—June to August.

    Astragalus oreganus (of the Oregon or Snake River, a misnomer) Nutt, ex T. & G., Fl. N. Amer. 1: 335. 1838 ("Oreganus").—"Plains of the Rocky Mountain Range towards the sources of the Oregon ... Nuttall."—Holotypus, BM! isotypus, NY!

    Astragalus ventorum (of the winds, or Wind River) Gray ex Wats. ap. Parry in Amer. Midl. Nat. 8: 212. 1874.—"Collected on Wind River."—Holotypus, C. C. Parry 65, collected in 1873 on the Northwest Wyoming Expedition, GH! isotypus, K!—Tragacantha ventorum (Gray) O. Kze., Rev. Gen. 949. 1891.

    The Wind River milk-vetch, A. oreganus, is presumably a recent derivative of A. canadensis var. brevidens with which it has in common almost all important technical characters. The flowers and pods are essentially identical in structure, but A. oreganus has acquired a certain individuality of aspect correlated with its adaptation to an arid environment Wherever I have seen it, A. oreganus is a pronounced xerophyte, but the xerophytic specialization is not absolute, for the species has been found in Fremont County in "wet places on alkaline flats" (Beetle 4545, RM), a situation where one would expect to find var. brevidens at home. As compared with the average var. brevidens, the Wind River milk-vetch is a dwarfer plant, remarkable for the slenderness and length of the cordlike rhizomes, for the short stems commonly branching into fan-shaped sprays of foliage, and for the comparatively few pairs of broad, emarginate leaflets. As a rule, the peduncles are shorter and the pod proportionately or absolutely broader than in var. brevidens. Nevertheless it has become increasingly difficult, as material has accumulated, to distinguish A. oreganus by constant or substantial differential characters. Its range fits neatly into a gap in that of var. brevidens, fulfilling the conditions of a geographic subspecies. In habit of growth A. oreganus resembles A. camptopus of southwestern Idaho, a species also found on dunes and barren sandy bluffs or knolls. The affinities of the two species are exceedingly remote, but the similarity is worth noting as an example of parallel evolution shaped by circumstance.

    Long known only from Nuttall's meagre type-collection, which has flowers only, A. oreganus was referred by Gray (1864, p. 202) to sect. Ocreati next to A. flavus and A. humistratus. This interpretation was natural enough in absence of the bilocular fruit, for A. oreganus has the connate stipules and dolabriform vesture of the Ocreati and Humistrati, even though its rhizomatous habit and nodding flowers are so very different. Because of Gray’s misunderstanding of its true nature and affinity, A. oreganus was not recognized in Parry’s rediscovery on the Wind River, and this accounts for the description of A. ventorum. A much later collection from the Red Desert near Superior, Wyoming (Steamboat Mountain, A. Nelson 7051, cited above) was distributed under a third name, A. solitudinis. This name appeared in print in a fragmentary discussion (probably intended to be withdrawn in press) in Nelson’s "New Plants from Wyoming XIV" (in Bull. Torr. Club 29 : 402. 1902, following a note on Trifolium scariosum). So far as I can learn, A. solitudinis was not associated with a published description and is a nomen nudum.