Astragalus alpinus L.
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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(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
"Habitat in Alpibus Lapponicis, Helveticis."—Holotypus labeled "Astragalus alpinus. Lapp.," LINN!
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Description
Species Description - Low, weak-stemmed, caulescent or apparently acaulescent, with a slender, oblique or vertical (seldom collected) initial taproot giving rise to horizontally creeping or obliquely ascending, at length repeatedly forking and adventitiously rooting, subterranean caudex-branches, the stems of the year aerial for a space of (0) 1-30 cm., commonly branched at the early emersed nodes, decumbent or incurved-ascending, each forming a small individual leafy tuft but these often running together into extensive patches or loosely woven carpets, the herbage ± strigulose, pilosulous, or villosulous with straight and appressed, straight and ascending, or more rarely ascending and curly or sinuous hairs up to (0.45) 0.5-0.9 mm. long, the leaflets sometimes equally pubescent on both sides but more often less densely so, or medially glabrescent, or quite glabrous above, the inflorescence nearly always black-hairy; stipules herbaceous becoming papery and brownish, or in age pallid and scarious, ovate, obovate, or broadly lanceolate, obtuse or subacute, 1.5—8 mm. long, mostly broader than the stem, the lowest ones shortest, connate at least at base and often through half their length into a loosely amplexicaul sheath; leaves (2) 3—11 (14) cm. long, with slender petiole and (11) 15-25 (27) mostly oval-ovate or -obovate, or suborbicular, obtuse or retuse, sometimes lance-elliptic and then either obtuse or subacute, flat, thin- textured leaflets 2—20 (24) mm. long; peduncles erect or incurved-ascending, (2) 3-13 (17) cm. long, either longer or shorter than the leaf; racemes shortly and at early anthesis rather densely (5) 7-17 (23)-flowered, the flowers ascending in bud, early spreading and at full anthesis nodding (therefore ± retrorsely imbricated), the axis little elongating, 0.5—4 (7) cm. long in fruit; bracts submembranous, pallid or green-tipped, ovate-triangular, lanceolate, or linear-lanceolate, 1-2.5 mm. long; pedicels slender, very early arched out- and downward, at anthesis 0.5—1.6 mm., in fruit 0.7—2.3 mm. long, not or scarcely thickened; bracteoles O; calyx 3.2—6.3 mm. long, densely (sparsely) strigulose-villosulous with black and often some (as long or longer) white, exceptionally all white hairs, the slightly oblique disc 0.5—1 mm. deep, the membranous tube 2-4.1 mm. long, 1.3-3.6 mm. in diameter, the subulate or triangular-subulate teeth 0.9-2.8 mm. long, the ventral pair nearly always broadest and shortest, the orifice ± oblique, the whole becoming papery, marcescent unruptured; petals commonly bicolored, whitish proximally, the banner- blade broadly margined and veined or striped, the keel-tip maculate with pale or dark bluish-lavender, the wings pallid or white, rarely all purple (drying bluish- purple); banner moderately to quite strongly recurved, ovate-cuneate or somewhat rhombic-ovate, deeply or shallowly notched, (6.2) 7.4-13.6 (14.8) mm. long, (3.8) 4.6-8 (8.8) mm. wide; wings a little shorter, (6) 7-11.6 (13.1) mm. long, the claws gently incurved, the blades linear-oblong, narrowly elliptic-oblanceolate, rarely lanceolate, obtuse, or more rarely obovate and obtuse to erose-emarginate, straight or nearly so; keel varying from 0.5 mm. longer to 2.2 mm. shorter than the banner and from 1.8 mm. longer to 1.6 mm. shorter than the wings, the claws relatively short, the blades large, prominent, obliquely triangular or triangular-obovate, abruptly incurved through 75-90° to the broad, blunt apex; anthers 0.4-0.65 (0.7) mm. long; pod pendulous, stipitate, the slender stipe 1.4-3.5 mm. long, the body ellipsoid or half-ellipsoid, (6) 7-15 mm. long, 2.5-4.2 mm. in diameter, straight or gently lunate-incurved, abruptly cuneate or cuneately tapering at base, contracted distally into a short, subulate, cusplike beak, triquetrously compressed, carinate ventrally by the slender, straight or gently concave suture, the lateral angles obtuse, the lateral faces almost flat, the dorsal face widely and shallowly sulcate, the thin, green, finally papery-membranous and greenish-stramineous valves either villosulous or strigulose with black, mixed black and white, rarely all white hairs up to 0.2-0.8 mm. long (exceptionally glabrous), inflexed as a hyaline partial septum 0.2-0.7 mm. wide; ovules (5) 6-9 (11); seeds brown, reddish-brown, ochraceous, or pale yellowish, smooth or nearly so, dull, 1.8-3 (3.2) mm. long.
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Discussion
The alpine milk-vetch is the most widely dispersed of all astragali, yet when due allowance has been made for the diversity of soils, climates, and environments to which it has become adapted, it is a comparatively little variable species. Throughout a vast spatial and altitudinal range of dispersal the pod remains essentially uniform within a comprehensible (and in the context of the genus expectable) span of variation in length, width, and curvature. The principal segregates from A. alpinus distinguished in the past have been characterized by slight differences in size, coloring, and relative lengths of the petals, the taxonomic value of which is discussed below under the heading of the typical variety. An informed opinion on the whole racial situation in the species must be based on representative material from its whole range. Ample material of A. alpinus from Scandinavia and the European Alps has been available for comparison with the American plant, but a disproportionately small sample of central, eastern, and arctic Asian populations has prevented a thorough review of the whole problem. The following key is designed primarily for use in America.