Astragalus americanus

  • Title

    Astragalus americanus

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus americanus (Hook.) M.E.Jones

  • Description

    2.  Astragalus americanus

    Robust, often coarse, amply leafy, the base of the stems and lower surface of the earliest (sometimes of all) leaves thinly villous with fine, spreading, and some retrorse, nearly straight or curly hairs up to 1-1.5 mm. long, the vesture commonly becoming shorter, sparser, and sometimes subappressed upward, the herbage green, but the leaflets conspicuously bicolored, pallid or subglaucescent beneath, green and glabrous above; stems erect and ascending, 3-7 (10, exceptionally only 1.5-2) dm. long, stout, striate, stramineous, usually hollow, leafless at base, simple or bearing slender spurs or branchlets at 1-4 nodes preceding the first peduncle; stipules very large and conspicuous, thinly herbaceous becoming papery-membranous in age, several-nerved, the lowest united behind the suppressed petiole into an entire, semiamplexicaul sheath, the rest broadly oblanceolate to elliptic-obovate, obtuse, embracing half or less than half the stem’s circumference, early deflexed; leaves 6-16 cm. long, shortly petioled or the uppermost subsessile, with (7) 9-13 (15) broadly lance- or ovate-oblong, or elliptic, obtuse (sometimes minutely mucronulate) or shallowly emarginate, flat, thin-textured, reticulately veined leaflets (0.8) 1.5-6 cm. long; peduncles erect, rather slender, (3.5) 5-14 (19) cm. long, mostly equaling or shorter than (the lowest sometimes surpassing) the leaf, the racemes usually not projected beyond the uppermost leaves; racemes loosely but shortly 10-25 (30)-flowered, the flowers nodding, the axis not much elongating, (1) 2-5 cm. long in fruit; bracts thinly herbaceous, several-nerved, becoming deflexed and papery, oblanceolate, obtuse, 4.5-9 mm. long; pedicels subfiliform, thinly or minutely strigulose-villosulous with white or black hairs, ascending in bud, early arched outward or bent at base and horizontally spreading, or loosely refracted, at anthesis (3) 3.5-5 mm., in fruit 4.5-9 mm. long; bracteoles either 0, or when present attached to the pedicel at a point 2-3 mm. below the calyx; calyx (4.5) 5.3-6.3 mm. long, glabrous or nearly so below the white- or sometimes partly black-ciliate teeth, the oblique disc 1—1.4 mm. deep, the pallid, campanulate tube (4.3) 4.9—5.8 mm. long, 3—3.8 mm. in diameter, the broadly low-deltoid teeth 0.2-0.7 mm. long, often reduced to a shallow crenulation of the obliquely truncate orifice, the whole becoming papery, marcescent unruptured; petals white or pale cream-colored, little graduated; banner gently recurved through ± 35°, spatulate or broadly rhombic-oblanceolate, shallowly notched, (10.6) 11.6-14.2 mm. long, 6.3-8 mm. wide; wings (0.1-1.4 mm. shorter) 10.5-13.4 mm. long, the claws 5.6-7.4 mm., the narrowly oblong, obtuse or suberose blades (5.5) 6.2-7.4 mm. long, 1.6-2.3 mm. wide; keel 10.3-12.7 mm. long, the claws (5.5) 6-7.3 mm., the lunately half-elliptic blades (5) 5.3—6 mm. long, 2—2.5 mm. broad, gently incurved through 40-85° to the rounded apex; anthers (0.4) 0.45-0.6 (0.65) mm. long; pod loosely pendulous, stipitate, the stipe 4.5-7 mm. long, the obliquely ellipsoid body 2-2.8 mm. long, 6.5-9.5 mm. in diameter, tapering at both ends, bladdery- inflated, laterally compressed at base and the ventral suture there strongly convex- arcuate and prominent, thereafter somewhat dorsiventrally compressed, the ventral face low-convex, the dorsal face flattened, the thin, green, glabrous or minutely black-strigulose valves becoming papery and subdiaphanous, not inflexed; ovules 6-8 (9), commonly 7; seeds olive-brown, smooth but dull, 2.4-2.8 mm. long.—

    Collections: 77 (o); representative: Eastwood 421 (CAS, WS);Porsild & Breitung 10,684 (NY); Cody & McCanse 2718 (CAS); /. W. & E. M. Thompson 338 (CAS, NY, RSA, WS, WTU); W. A. Weber 2365 (NY, WS, WTU); Hitchcock & Martin 7876 (WS, WTU); J. Macoun 65,087, 65,088 (NY); C. L. Hitchcock 16,786 (NY, RSA, WS), 18,345 (ID, NY, RSA, WS); Cronquist 8094 (NY, RSA, widely distributed); Hall & Harbour 137 (CAS, NY); Marie-Victorin & al. 33,844 (CAS, NY, OB, PH).

    Meadows, brushy stream banks and lake shores, often about willow thickets and aspen groves, or at the edge of fir or spruce woods, sometimes on rock debris at the foot of cliffs or on shaded rock ledges, near sea level northward and up to 7200 feet in the Rocky Mountains, widespread and locally plentiful from upper Yukon Valley, eastern Alaska and Yukon, to Great Slave Lake, south to southern British Columbia and (east of the Continental Divide) along the main Cordillera to northwestern Wyoming; isolated in Colorado (± lat. 40° N., perhaps on the headwaters of the South Platte, not seen since Hall & Harbour), in the Black Hills, South Dakota, and in the Cypress Hills, southern Saskatchewan; east interruptedly through central Manitoba to the south shore of Hudson Bay, Ontario, and on Gaspe Peninsula, Quebec.—Map No. 1.—Late June to August.

    Astragalus americanus (Hook.) Jones, Contrib. West. Bot. 8: 8. 1898 ("Americanus"), based on Phaca frigida P americana (American) Hook., FI. Bor .-Amer. 1: 140. 1831 ("Americana"""" ).—Woody regions of the Rocky Mountains in lat. 52° to 56°, to Slave Lake in lat. 61°. Dr. Richardson and Drummond."—Holotypus, Richardson 276, K! paratypus (Drummond from the Rocky Mountains), K!—Astragalus frigidus var. americanus (Hook.) Wats., Bibl. Ind. 193. 1878 ("Americanus"). A. alpinus var. americanus (Hook.) Sheld. in Minn. Bot. Stud. 1: 133. 1894. Phaca americana (Hook.) Rydb. ap. Britt. & Br., Lll. Fl. 2: 304, fig. 2148. 1897.

    Astragalus americanus fma. glabrescens (becoming hairless) Rouss. in Contrib. Lab. Bot. Univ. Montreal 24: 50. 1933.—"...Kicking Horse Lake, British Columbia, Aug. 11th, 1890, Jas M. Macoun ... "—Holotypus, US!

    Astragalus americanus fma. pallescens (turning pale) Rouss. in op. cit.: 51. 1933.— "Dakota du Sud: Deerfield, July 11, 1930 (A. C. McIntosh 1476)... "—Holotypus, collected July 18, 1930, NY!

    Astragalus americanus fma. Williamsii (Thomas Albert Williams, 1865-1900) Rouss. in op. cit.: 51. 1933.—"Wyoming: Welcome, July 26, 1897, T. A. Williams ... "—Holotypus, NY!

    Astragalus gaspensis (of Gaspé) Rouss. in op. cit.: 51, figs. 13, 15, 16. 1933.—"Province de Quebec, p6ninsule de Gaspé... Little Cascapedia River, July 17, 1905 (Collins & Fernald, 107; specimen en fleurs. Cotype: Gray Herbarium...); riviere Petite Cascapedia, sur le talus rocheux a 5 milles de 1’embouchure, 10 aout, 1930 (Victorin, Rolland & E. Jacques, 33826; specimen en fruits. Type dans l’herbier de l’Universite de Montreal)."—Holotypus, not examined; cotypus, GH!—A. frigidus var. gaspensis (Rouss.) Fern. in Rhodora 39: 312. 1937.

    The American milk-vetch is easily distinguished from other tall, amply leafy Astragali of moist montane and forested regions of North America by its unifoliolate lower stipules and its pendulous, stipitate, swollen pod of subdiaphanously papery texture. It was subordinated by early writers to the Eurasiatic A. frigidus, from which it differs in its ordinarily greater stature, shorter, glabrous calyx-tube, long fruiting pedicels, and glabrous or minutely pubescent (not villosulous) pod. Despite its wide and interrupted range it is a comparatively uniform and stable species, the formae described by Rousseau being taxonomically insignificant variants of an extremely minor nature. The fma. glabrescens is the state characterized by a puberulent pod, sometimes found in the same population as the more ordinary glabrous one (e.g., Hitchcock & Muhlick 13,486, strigulose at NY, RSA, hairless at CAS; or Tweedy 3174, pubescent at WS, glabrous at NY). The fma. pallescens, described from fairly fresh material, supposedly had a whitish calyx and pure white rather than creamy petals, but the typus can no longer be distinguished from other specimens of the same age. The fma. Williamsii had wing-petals bearing a rudimentary auricle on the exterior margin, an approach to symmetry which occurs sporadically in perhaps half our species. The case of A. gaspensis is different chiefly on account of its great spatial isolation from the main Cordilleran range of A. americanus, although intermediate stations are now on record from Manitoba and Hudson Bay. Rousseau distinguished A. gaspensis on the basis of longer calyx-teeth separated by narrower sinuses and a pod supposedly shorter and obtuse rather than attenuate at either end. The difference in shape of the fruit as illustrated by Rousseau (op. cit., fig. 13) is considerably exaggerated; the photograph (fig. 15) portrays a fruit which can be matched very precisely by some Rocky Mountain examples of A. americanus. The calyx-teeth of the Gaspesian plant are sometimes as little as 0.5 mm. long, when they lie well within the range of variation of the Cordilleran type. Calyx-teeth averaging a few tenths of a millimeter longer seem to be the only differential character of A. gaspensis and scarcely justify even the varietal rank to which it was reduced by Fernald.