Astragalus pterocarpus

Sparsely leafy, somewhat wiry or junceous, with a shortly forking caudex or stout, multicipital root-crown just below soil-level, strigulose with filiform or commonly flattened, straight, appressed hairs up to 0.35—0.65 mm. long, the stems and lower leaf-surface thinly so, the herbage pallid or bluish-green when fresh, the leaflets densely silvery-canescent above; stems many, erect, the outer ones decumbent and ascending, (1) 1.5-3.5 (4) dm. long, simple and leafless at base, branching at 1—3 nodes preceding the first peduncle, flexuous or zigzag distally, the branches interlacing and forming bushy clumps of low, rounded outline; stipules 2.5—7 mm. long, the lowest ones scarious, obtuse, almost fully amplexicaul, free, the upper ones firmer or herbaceous, narrower, with deltoid, triangular-acuminate, or lanceolate, erect or deflexed blades; leaves (3.5) 5-10 cm. long, shortly petioled, with 1—3 (4) distant pairs of linear-acuminate or linear, acute or subacute, flat, dorsally keeled leaflets 1—5 cm. long, all continuous with the slender, grooved rachis, sometimes reduced in size or absent in the uppermost leaves, the terminal one represented by a linear, tapering production of the rachis and usually much longer than the last pair; peduncles at first ascending, then bent downward by weight of the succulent fruits, (4) 5—11 (15) cm. long, usually surpassing the leaf; racemes loosely but shortly 5—15-flowered, the flowers ascending, becoming horizontal in age, the axis little elongating, (1) 2—8 cm. long in fruit; bracts membranous, ovate- or lance-acuminate, 1-5 mm. long; pedicels at anthesis ascending, 1.2-2.2 mm. long, in fruit arched out- or downward, thickened, 1.8-2.8 mm. long; bracteoles 0-2, usually present, scarious; calyx 9-12 mm. long, pilosulous with black or mixed black and white hairs, the pallid, membranous, cylindric but often basally tapering tube 7-8.5 mm. long, 2.8-3.6 mm. in diameter, the subulate teeth 2-4 mm. long, the ventral pair often a trifle the longest, the whole becoming hyaline, irregularly circumscissile; petals purple or whitish tipped with purple (not seen fresh), the banner with a pale, striate eye in the fold; banner broadly rhombic- oblanceolate, 16.3-19 mm. long, 7.4-9.2 mm. wide; wings 13.8-16.7 mm. long, the claws 7.4-9 mm., the oblong or oblong-obovate, obtuse, straight or distally incurved blades 7-8.6 mm. long, 1.9-2.8 mm. wide; keel 12.8-15.5 mm. long, the claws 7.5-9 mm., the half-obovate blades 5.9-7 mm. long, 2.6-3.2 mm. wide, gently incurved through 80-95° to the blunt apex; anthers (0.55) 0.6-0.9 mm. long; pod pendulous, sessile, elliptic or broadly oblong-oblanceolate in dorsiventral view, (2.5) 3-4.5 cm. long, (1.1) 1.3-1.7 cm. wide, nearly straight or obscurely sigmoid-arcuate below the decidedly incurved, triangular-acuminate, laterally flattened beak, the body very strongly obcompressed and hardly more than 3 mm. thick, the ventral face widely and shallowly grooved, the dorsal face flat or commonly low-convex, the lateral angles narrow but obtuse when fresh, at length margined all around, except at very base and in the beak, with a thin, rigid wing 2-3 mm. wide, the sutures both prominent, the ventral one depressed and the two subcontiguous within the cavity, the pale green, subtranslucent, smooth, fleshy, glabrous valves shrinking in ripening, ultimately leathery, stramineous, lustrous, transversely rugulose-reticulate, not inflexed; dehiscence basal and upward through the ventral suture, and simultaneously through the beak; seeds brown, smooth or sparsely punctate, 2—3.4 mm. long.—Collections: 8 (ii); representative: Jones 3835 (CAS, ORE, POM), in May, 1903 (CAS, POM, US, WS), 25,439 (CAS, POM); Ripley & Barneby 6169 (CAS, GH, NA, NY, RSA).

Low gullied hills and alkaline sandy flats, saltgrass meadows, and openings among halophytic shrubs, 4450—4500 feet, local but forming colonies, fairly frequent along the Humboldt River from near Battle Mountain downstream about 10 miles, in southeastern Humboldt and adjacent Lander Counties, Nevada; also about 80 miles to the west in southcentral Humboldt County (near Jungo).—Map No. 108.—April to June.

Astragalus pterocarpus (with winged fruits) Wats., Bot. King 71, Pl. XII, fig. 1. 1871. —"... near the junction of Reese River with the Humboldt, Nevada ... [Watson No.] 272.—Holotypus, collected in September, 1868, US! isotypi, GH, NY!—Tragacantha pterocarpa (Wats.) O. Kze., Rev. Gen. 947. 1891. Pterophacos pterocarpus (Wats.) Rydb. in N. Amer. Fl. 24: 308. 1929.

The sparsely leafy, somewhat rushlike stems of the winged milk-vetch and its few decurrent leaflets, often reduced in size or altogether lacking in the upper leaves, are reminiscent of some seleniferous Pectinati, but these differ greatly in their connate stipules and persistent fruits of altogether different shapes. Only A. toanus of sect. Pectinati extends west as far as the Humboldt Valley, and this is distinguished further by its short leaflets and narrowly ascending, more loosely racemose flowers. The exceptionally long and narrow leaflets of A. pterocarpus, silvery-canescent above and glabrescent beneath, are remarkable enough in their own way, but the pod cannot fail to arouse a sentiment of admiration mingled with wonder. The large, fully formed but as yet unripe, shieldlike fruit is perfectly smooth, succulent, and of a pale green, semitranslucent substance suggestive of worked jade. At this stage the lateral angles (illustrated in Barneby, 1956, frontispiece) are relatively thick and rounded and the whole fruit heavy with juice. During the process of ripening, the sap is withdrawn from the fleshy mesocarp, as the watery tissues collapse inward, the sharp, thin, but rigid wings assume their characteristic form. The dry, fully ripe pod is leathery, straw-colored, lustrous, and prominently cross-reticulate. In the sum of all its characters the fruit of the winged milk-vetch is unique, but it is interesting that laterally winged pods, comparable in external form even though much smaller, thinner-textured, and bilocular, have evolved in two annual astragali, closely related neither to one another nor to A. pterocarpus, the central Asiatic A. Thlaspi Lipsky and the Mexican A. scutaneus.

The winged milk-vetch was said by Jones (Contrib. West. Bot. 17: 12) to have been "obliterated at the type-locality" by 1930. However, a vigorous colony was still thriving at the mouth of the Reese River in the summer of 1944, and the species is certainly holding its own on the flood-plain of the Humboldt River downstream from Battle Mountain. Colonies vary in extent from year to year, but as the plants are apparently avoided by cattle, the species is in no immediate danger of extermination.