Astragalus speirocarpus
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Title
Astragalus speirocarpus
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Authors
Rupert C. Barneby
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Scientific Name
Astragalus speirocarpus A.Gray
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Description
82. Astragalus speirocarpus
Rather slender, with a woody taproot and shortly forking or knotty caudex, densely strigulose with subappressed and arcuate-incumbent hairs up to 0.3-0.5 mm. long, the herbage cinereous or rarely greenish, the leaflets often brighter green and more thinly pubescent above than beneath; stems several or numerous, weakly ascending or diffuse, 1-3.5 dm. long, simple and leafless at base, usually branched or spurred at 1-3 nodes preceding the first peduncle, the main axis composed of ± 6-11 intemodes; stipules (1) 1.5-4 (5) mm. long, the lowest mostly ovate, obtuse, early becoming papery and brownish, amplexicaul-decurrent around 1/2-4/5 the stem’s circumference, the median and upper ones shorter, narrower, with deltoid or triangular, erect or deflexed blades; leaves 1.5-7.5 cm. long, all subsessile or the lowest shortly petioled, with 7-17 (21) cuneate-oblanceolate, oblong, cuneate-obcordate, or inversely deltoid, truncate to deeply retuse, mostly flat leaflets 2-10 (12) mm. long; peduncles erect or incurved-ascending, (1) 2-5 (6.5)
cm. long, usually much shorter than the leaf; racemes loosely, at first anthesis rather closely, (3) 7-17 (20)-flowered, the axis a little elongating, 1-3.5 (5) cm. long in fruit; bracts membranous, ovate or lanceolate, 1-2.5 mm. long; pedicels at anthesis slender, ascending, 1-1.5 mm. long, in fruit thickened, arcuately spreading or declined, 1—2 (2.5) mm. long; bracteoles commonly 2; calyx 5.2-8 (9.1) mm. long, villosulous with spreading and incumbent, black or mixed black and white hairs, the somewhat oblique disc 0.9-1.4 mm. deep, the deeply campanulate or subcylindric tube 4.7-7.3 mm. long, 2.6-3.8 mm. in diameter, the broadly subulate or triangular, obtuse teeth 0.5-1.2 mm. long, the ventral pair commonly shortest and broadest, the whole becoming papery, marcescent unruptured; petals whitish or lilac-tinged, the keel tipped with dull purple; banner rhombic-obovate or -oblanceolate, 14.7-20 mm. long, 5.8-9 mm. wide; wings 12.1—17.2 (18) mm. long, the claws 6.2—8.1 (9.1) mm., the narrowly oblong, obtuse or subemarginate, nearly straight blades 7-10.2 mm. long, 1.6-2.7 mm. wide; keel 10.6-13 (14.5) mm. long, the claws 6.3-8 (9) mm., the broadly half- elliptic blades 4.8-6 (6.4) mm. long, 2.3-3.2 mm. wide, incurved through 85-95° to the rounded apex; anthers 0.5—0.75 mm. long; pod pendulous, declined, or (from humistrate peduncles) horizontally spreading, stipitate, the stipe (4) 5-11 mm. long, proximally straight or slightly arched downward, then incurved and gradually expanded into the body, the body linear-oblong, (2-7) 3.2-5 (6) mm. wide, coiled into a flat spiral through 1¼-2½ circles, or by twisting through different planes elaborately and irregularly contorted, acuminate at apex, strongly compressed, bicarinate by the salient sutures, the ventral one often produced as a narrow, low-dentate wing, the faces nearly flat to low-convex, the somewhat fleshy, green or faintly mottled, strigulose valves becoming stiffly leathery and stramineous or brownish, the coarsely reticulate exocarp ultimately splitting along the sutures and exfoliating irregularly from the nearly smooth endocarp, the tardily splitting ventral suture tending to become detached and separating into two tough fibres; ovules (14) 20-28 (30); seeds (little known) soot-black, sparsely pitted, dull, (?1.8) 2.7—3.1 mm. long.—Collections: 29 (ii); representative: Griffiths & Cotton 45 (POM, WS); Piper 2758 (NY, WS); Hitchcock & Marsh 3331 (CAS, WS, WTU); J. W. Thompson 11,439 (CAS, NY, RSA, WS, WTU), 14,298 (CAS, NY, WTU).Dry hillsides and valley flats in stony or sandy soils overlying basalt, commonly in sagebrush scabland, 900—2000 (2600) feet, locally plentiful in the valleys of the Yakima and Columbia Rivers in Yakima and Kittitas Counties, Washington, extending south just into eastern Klickitat and western Benton Counties.—Map No. 30.—May to July.
Astragalus speirocarpus (with coiled pod) Gray in Proc. Amer. Acad. 6: 225. 1864.— "Wenass, in the valley of the Upper Columbia River, Dr. Lyall. ex herb. Kew."—Holotypus, Lyall's Phaca No. 1, collected in 1860, GH! isotypus, K!—Tragacantha speirocarpa (Gray) O. Kze., Rev. Gen. 948. 1891. Phaca speirocarpa (Gray) Piper in Contrib. U.S. Nat. Herb. 11: (Fl. Wash.): 370. 1906. Homalobus speirocarpus (Gray) Rydb. in Bull. Torr. Club 51: 18. 1924.
At anthesis the medick milk-vetch, A. speirocarpus, is not an especially distinguished astragalus, although the neat gray foliage and lilac-tinged (when dry, mostly ochroleucous) flowers are quietly attractive. The pod, however, is most remarkable, not only for its exactly spiral or sometimes spirally contorted curvature, but also for its mode of dehiscence, of which the last stage is still unknown. Gray (1864, l.c.) remarked of this and the preceding species, A. sclerocarpus, that both sutures of the pod tend to separate in age from the body in the manner of some Mimosoideae, but this does not always occur. The ventral suture, which is often narrowly winged, seems normally to split lengthwise into two parts as the pod ripens; and at the same time the exocarp, containing the externally prominent nervature, separates from both sutures and exfoliates from the endocarp in an irregular manner. The true dehiscence proceeds only a short way downward through the narrowly gaping beak and also a short distance upward through the stipe, but it is not known how the seeds near the middle of the spiral escape to the ground. Possibly they are released only through disintegration of the pod by winter weathering.
The close relationship between A. speirocarpus and A. sclerocarpus is evident especially in flowering plants, which are sometimes difficult to distinguish, and it is that much more remarkable that the range of the medick milk-vetch lies wholly within that of its commoner relative. There is no evidence that they are ever found closely associated; very possibly a more exact knowledge of their ecology will reveal that they are kept apart by some edaphic factor. So far as I can learn, A. speirocarpus is nearly always associated with sagebrush in a variety of light sandy or stony soils, whereas A. sclerocarpus is found most often on dunelike barrens of semidesert character where competition is less severe.