Astragalus argophyllus Nutt.
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Authors
Rupert C. Barneby
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Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
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Family
Fabaceae
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Scientific Name
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Type
"Vallies of the Rocky Mountains, near the sources of the Platte, Nuttall! -Holotypus, labeled "Astragalus * argophyllus. R. Mts., Columbia slope." BM! isotypi, GH, NY, P!
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Description
Species Description - Acaulescent or shortly caulescent, densely pilose or strigose throughout with appressed to narrowly or loosely ascending, straight, or sometimes partly sinuous hairs up to (0.65) 1-1.65 mm. long, the herbage silvery-silky, or somewhat greenish in age; stems 0-1 (1.5) dm. long, when developed prostrate and radiating, the internodes all short, rarely up to 2 cm. long, usually little longer or all shorter than the loosely imbricated stipules; stipules submembranous becoming papery, often brownish when old, 2-8 (10) mm. long, the lowest (often dorsally glabrate) and sometimes all ovate or broadly lanceolate, the upper ones commonly longer and narrower, decurrent-amplexicaul around half to the whole stem’s circumference, but the margins, even when in contact, not united; leaves 1.5-12 (15) cm. long, those subtending the peduncles sometimes much longer than the rest, all slender- petioled, with 7-21 rhombic-elliptic, oval-oblanceolate, or obovate-cuneate, acute or obtuse, distant or crowded, flat or loosely folded leaflets 2-15 mm. long; peduncles almost 0 to 9 cm. long, usually much and always a little shorter than the leaf, incurved-ascending at anthesis, arcuately reclinate or prostrate in fruit; bracts membranous or broadly membranous-margined, ovate or lanceolate, 1.8-6.5 mm. long; pedicels ascending or a trifle arched outward, at anthesis slender, 1.2-3.2 mm. long, in fruit a little thickened, 1.8-3.8 mm. long; bracteoles commonly 0, exceptionally present and up to 2.5 mm. long; calyx 9-16.8 mm. long, pubescent like the herbage with white and often some or nearly all black hairs, the somewhat oblique disc 1-2.5 mm. deep, the cylindric, pallid or purplish tube 6.5-11.8 mm. long, 2.8-4.6 mm. in diameter, the subulate or linear-subulate teeth 1.6-5 (5.8) mm. long, the whole becoming papery, ruptured, marcescent; petals either bright pink-purple (drying bluish), or tinged with lilac or dull purple; banner oblanceolate, broadly rhombic-oblanceolate, or spatulate, notched, 15-24 mm. long; wings a little shorter, the lance-oblong, obtuse blades rather abruptly narrowed and usually a little incurved in the distal third; keel 12.1-20.3 mm. long, the half- obovate or lunately elliptic blades 4.6-7.4 mm. long, gently incurved through 8090 (95)° to the blunt apex; anthers 0.45-0.85 mm. long; pod ascending (humistrate), varying from plumply ovoid-acuminate to narrowly lance-elliptic in profile, 1.5-3.2 (3.7) cm. long, 5-12 (13) mm. in diameter, either straight proximally and incurved into the deltoid or triangular-acuminate, laterally compressed beak, or gently incurved (through up to ½-circle) its whole length, obcompressed and dorsally flattened or very shallowly and widely sulcate in the lower ?, the ventral suture thick and prominent but sometimes depressed and lying in a double groove, the ± fleshy, green valves becoming brownish, stiffly leathery or woody, faintly to quite strongly rugulose-reticulate and sometimes also wrinkled lengthwise on the ventral side, thinly to densely strigulose or sometimes villous-villosulous, not inflexed; dehiscence apical, the ventral suture finally splitting but not separating; ovules 25-43; seeds brown, smooth or sparsely pitted, dull, 1.7-3 mm. long.
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Discussion
The silver-leaved milk-vetch, the species nomenclaturally typical of its section, is also by some happy chance the one which seems most nearly to represent a generalized prototype of the Argophylli. From A. argophyllus var. Martini it is possible to follow through several lines of modification involving small and sometimes parallel steps the probable course of evolution which has culminated in the more specialized forms. Being morphologically central to the section and serving as a point of contact (either directly or through its closest kindred) between subsections Eriocarpi and Newberryani (which lead on toward the more aberrant or peripheral groups), A. argophyllus might be thought directly ancestral to the remaining Argophylli. The species is, however, highly polymorphic and variable, characteristics which are seldom associated with age or a primitive condition.
The geographic races of A. argophyllus vary considerably in orientation of the vesture, in size and color of the flowers, and in ecology. It is only with difficulty that the material may be sorted into three main categories, and even if these pretty clearly correspond with real divergent lines of development, individual plants will surely be met with which cannot be placed satisfactorily by use of the following key.