Monographs Details: Astragalus pauperculus Greene
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

328.  Astragalus pauperculus

Slender, delicate, sometimes dimunitive, with one erect or more often 2-5 incurved-ascending stems arising from the cotyledons or first nodes, strigulose nearly throughout with straight, appressed or narrowly ascending hairs up to 0.3-0.5 mm. long, the herbage green or (when young) cinereous, the leaflets glabrous or thinly pubescent toward the margins above; stems 1-8 (11.5) cm. long, simple or bearing a slender spur or branchlet at 1—2 nodes preceding the first peduncle, purple-tinged, commonly floriferous from the middle or below; stipules broadly ovate or triangular-acuminate, 1-3 mm. long, submembranous, greenish or purplish becoming papery and brownish, about semiamplexicaul, glabrous or nearly so dorsally, the margins black- or white-ciliate and sometimes beset with a few minute processes; leaves 1.5-5 cm. long, with filiform petioles and (5) 7-11 rather remote, oblong-oblanceolate, obovate-cuneate, or exactly cuneate, truncate or commonly retuse, flat or loosely folded leaflets 2-8 mm. long; peduncles subfiliform, ascending or incurved-ascending at anthesis, divaricate or declined in fruit, 2.5-7 cm. long, surpassing the leaf; racemes loosely 2-5 (7)- flowered, the flowers at first ascending, usually declined and secund in age, the axis more or less elongating, (0.4) 0.7-2 cm. long in fruit; bracts membranous, pallid or purplish, ovate or lanceolate, 0.8-1.5 mm. long; pedicels at anthesis slender, ascending, 0.5-1.3 mm. long, in fruit thickened, either straight and ascending, arched outward and downward, or recurved and contorted, 0.8-1.5 mm. long; bracteoles 0, rarely a minute scale; calyx 2.9-4.3 mm long, strigulose with black and sometimes a few intermingled white hairs, the subsymmetric disc 0.4-0.7 mm. deep, the membranous, purplish tube 2.2-2.8 mm. long, 1.5-2.1 mm. in diameter, the subulate teeth 0.7-1.5 mm. long, the whole becoming papery-membranous, ruptured, marcescent; petals pink- or violet-purple, the banner with a pale, striate eye in the fold, the inner margins of the wings pale or white; banner recurved through ± 40°, ovate-cuneate, deeply notched, 5.4-10.5 mm. long, 3.7-7.3 mm. wide; wings a little shorter, 5.3-10.2 mm. long, the claws 1.8-2.5 mm., the oblanceolate, obtuse, truncate, or emarginate, nearly straight blades 4.1-8.4 mm. long, 1.4-2.9 mm. wide; keel much shorter than either wings or banner, 4.3-5.8 mm. long, the claws 1.9-2.7 mm., the half-obovate or nearly halfcircular blades 2.7-3.7 mm. long, 1.5-2.3 mm. wide, incurved through 95-110° to the broadly deltoid, sometimes minutely porrect apex; anthers 0.3-0.5 mm. long; pod deflexed, declined, or ascending and then commonly resupinate, sessile, narrowly crescentic in outline, 1.2-2 cm. long, 2.6-3.4 mm. in diameter, rounded at base, tapering distally into a short, triangular-acuminate, laterally flattened beak, otherwise bluntly triquetrous (becoming somewhat quadrangular when fully ripe), carinate ventrally by the thick suture, the lateral angles obtuse, the lateral faces at first low-concave becoming distended by the seeds, a little wider than the shallowly sulcate dorsal face, the thin, purplish or brightly purple-mottled, sparsely and minutely strigulose or rarely glabrous valves becoming papery, finely cross-reticulate, inflexed as a complete or subcomplete septum 1.4—2.3 mm. wide; ovules 8-12; seeds subquadrate, brown, sometimes purple-speckled, wrinkled but sublustrous, 2.2-3.2 mm. long.—Collections: 13 (ii); representative: A. Heller 11,286 (CAS, G, MO, ND, NY, US); Hoover 3236 (NY, WS); Barneby 11,491 (CAS, NY, RSA), 11,496 (CAS, RSA); /. T. Howell 2304 (CAS).

Stony flats and about shallow depressions or ephemeral rain pools in the foothills and rolling plains, in red sand or clay of volcanic origin, 450—2050 feet, locally plentiful in scattered stations along the west base of the Cascade Range about the upper waters of the Sacramento River in Shasta, Tehama, and Butte Counties, California.—Map No. 148.—March to early May.

Astragalus pauperculus (poor and little) Greene in Pittonia 3: 224. 1897.—"... first collected by myself now more than twenty years since, on a dry hillside of the upper Sacramento, but in flower only ... Fruiting specimens sent in recently from the same district indicate its close relationship to A. tener and A. Rattani—No Greene collection and no fruiting typus found at CAS, ND, or UC. Presumed holotypus, identified by Greene as A. pauperculus, labeled "Bluffs of Little Chico Creek, May, 1896, Mrs. R. M. Austin," in flower only, ND!

Astragalus tener var. Bruceae (Carola Josephine, daughter of Rebecca Merritt Austin, afterward Mrs. Charles Clinton Bruce, 1865-1931, amateur botanist active in n.-e. California and adjoining Oregon, often in the company of her mother) Jones, Rev. Astrag. 268, Pl. 68. 1923 ("Brucae").—"No. 2430 Mrs. Bruce, plains of Butte Co., blooming in March."—Holotypus, collected in 1898, POM! isotypus, NY!—Hamosa Bruceae (Jones) Rydb. in N. Amer. Fl. 24: 426. 1929. Astragalus Bruceae (Jones) Abrams, I11. Fl. Pac. St. 2: 603, fig. 2893. 1944.

The Bruce milk-vetch, A. pauperculus, is a delicate and delightful little astragalus, closely related to A. tener and A. Rattani as Greene pointed out, but easily distinguished from both by its loose fruiting raceme (over 1 cm. long when, as most often, over 2-flowered), and from A. Rattani var. Jepsonianus in particular by its comparatively short pod rounded rather than acuminately tapering at base. In the related species the pod is either green or suffused with purple on the side exposed to maximum sunlight, while that of the Bruce milk-vetch is nearly always brightly mottled with purplish-red, the mottlings sometimes running together into a deep purple field. Because of the great variation in the curvature of the fruiting pedicels, the ripe pod is variably oriented, perhaps most often declined or deflexed, but almost as often ascending and resupinate as in the desert-dwelling A. acutirostris. Quite variable in stature, some plants of A. pauperculus flower from very early nodes close to the ground, and even the most vigorous individuals rarely exceed a decimeter in height.

So far as my information goes, A. pauperculus is the only representative of its group on the west slope of the Sacramento Valley in Shasta and Tehama Counties, where it is apparently confined to volcanic soils. In Butte County it has been found at low elevations on the valley floor, where it overlaps the range of A. Rattani var. Jepsonianus (poorly illustrated by the map, due to lack of precise data). Field studies should be undertaken in this area to determine whether and in what way the species are ecologically separated. Although sometimes occupying the bed of shallow vernal pools in the foothills, the Bruce milk-vetch is by no means characteristic, as is A. tener, of soils waterlogged in early spring. It seems most vigorous and most at home on well-drained slopes, rooting in a porous medium of red, tindery gravels mixed with a little humus.