Astragalus recurvus

  • Title

    Astragalus recurvus

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Astragalus recurvus Greene

  • Description

    28. Astragalus recurvus

    Low, diffuse, rather slender perennial, with a woody, ultimately very stout taproot and shallowly buried, pluricipital root-crown or shortly forking caudex, thinly strigulose with fine, straight, appressed hairs up to 0.3-0.45 mm. long, the herbage green, the leaflets glabrous above; stems several or many, decumbent with ascending tips, 1-2 dm. long, leafless and subterranean for a space of 1-4.5 cm., simple or sparingly branched from near the base or at 1-3 nodes preceding the first peduncle; stipules 1.5-4 mm. long, membranous becoming papery, often purple-tinged, connate-amplexicaul, the lowest into a bidentate or subtruncate sheath, the median and upper ones united through half their length or less, with triangular, mostly erect blades; leaves (1.5) 3-7 cm. long, petioled but the uppermost shortly so, with 9-19 oblong-obovate, elliptic, or linear-oblong, obtuse or emarginate, flat or loosely folded leaflets 2-10 mm. long; peduncles mostly incurved-ascending, 3—10 cm. long; racemes loosely (5) 7—25-flowered, the flowers at first ascending, then spreading, ultimately declined, the axis 1.5—9 cm. long in fruit; bracts membranous, ovate or triangular-lanceolate, 0.5—1.5 mm. long; pedicels at anthesis slender, ascending or a trifle curved, 0.5—1.5 mm. long, in fruit somewhat thickened, arched outward, downward, or deflexed, 1—2.4 mm. long, tardily disjointing with the fruit; bracteoles 0; calyx 3.5—4.7 mm. long, strigulose with white, or with white and black hairs, the subsymmetric disc 0.5—0.9 mm. deep, the campanulate tube 2—3.2 mm. long, 1.8—2 mm. in diameter, the subulate teeth 1-1.6 mm. long, the whole becoming papery, marcescent usually unruptured; petals whitish tinged with sordid lilac; banner recurved through 65—90 , ovate- cuneate, 5.2-1.1 mm. long, 4-5.8 mm. wide; wings nearly as long or a trifle longer, 8 mm. long, the claws 1.7—2.6 mm., the obliquely elliptic-oblanceolate or tri- angular-obovate, obtuse blades 3.9—6 mm. long, 1.8—2.7 mm. wide, the left one more strongly incurved than the right; keel 5—6.5 mm. long, the claws 1.9—2.7 mm., the crescentic blades 3.5—4.7 mm. long, 1.8-2.3 mm. wide, incurved through 50-95° to the sharply triangular apex; anthers 0.4-0.65 mm. long; pod pendulous, sessile or nearly so, the stipe when present not over 0.7 mm. long, the body linear- oblong or -elliptic in profile, strongly curved downward, 1.3—2.5 cm. long, 2.3—3 mm. in diameter, cuneate or acuminately tapering at either end, compressed-triquetrous, keeled ventrally by the prominent suture, the low-convex lateral faces much wider than the narrowly and rather deeply grooved dorsal face, the thin, green, sometimes purplish-tinged, finely strigulose valves becoming papery, stramineous, cross-reticulate, inflexed as a nearly complete septum 0.7-1.5 mm. wide; dehiscence through the length of the ventral suture, the walls of the septum also separating in age; ovules 12—18; seeds brown or olivaceous, rugulose-punctate but somewhat lustrous, 1.9-2.8 mm. long.—Collections: 12 (iv); representative: Deaver 2475 (CAS); Ripley & Barneby 8458 (CAS, NY, RSA, UTC); Barneby 12,648 (CAS, POM, RSA, US), 12,650 (CAS, NY, RSA); MacDougal 72 (ARIZ, NY).

    Open places in forest of yellow pine, mixed oak and pine, or juniper, in dry stony volcanic soils, 4800-7050 feet, locally plentiful but not frequent, Flagstaff Plateau and headwaters of the Verde River, southern Coconino and central Yavapai Counties, southeast to Sierra Ancha and the head of Tonto Creek on the slopes of the Mogollon Escarpment in northwestern Gila County, Arizona.—Map No. 11—April to early July.

    Astragalus recurvus (bent backward, of the decurved pod) Greene in Bull. Calif. Acad. Sci. 1: 157. 1885.—"Mountains of the northern part of Arizona, 1883, Dr. H. H. Rusby."— No typus found at CAS, ND, NY, UC, or US, but possibly overlooked or mislaid, as Rydberg (1931, p. 405) cities "Rusby in 1883 (type)" and Jones (1895, p. 636) mentioned a type- specimen being "very poor and in fruit only." The holotypus should be at CAS, and was possibly lost at the time of the San Francisco fire.—Tium recurvum (Greene) Rydb. in N. Amer. Fl. 24: 397. 1929.

    The recurved milk-vetch was appropriately named in reference to its slenderly oblong- ellipsoid pod which is arched downward in a gentle lunate curvature to form in profile the figure of an inverted crescent. The detached fruit is similar in form to that of A. atratus with which it was referred by Rydberg (1929, l.c.) to Tium sect. Atrata, a group remote from Strigulosi by reason of its free stipules and differently shaped flowers. The relationship of A. recurvus to the present section was appreciated by Jones, although he associated it with A. straturensis, another species with free stipules, here referred to sect. Miselli. The recurved milk-vetch and A. straturensis both have small, loosely racemose flowers; specimens of the latter with immature fruits have been misidentified as A. recurvus, giving rise to reports of it from the Grand Canyon (Jones, 1923, p. 186) and southern Utah. Apart from the morphological differences, A. straturensis is strongly calciphile, whereas A. recurvus is known only from soils derived from the decay of comparatively recent lavas and volcanic cinders.

    While mature fruiting material of A. recurvus is easily recognized, care should be taken to distinguish younger specimens from the related A. Rusbyi, also endemic to basaltic soils in central Arizona, and similar in most technical characters. The latter differs in its slightly more numerous (17—25 rather than 9—19) leaflets in vigorous leaves, and in the wing-petals which very prominently surpass the strongly recurved banner. The recurved milk-vetch begins to flower in April or early May and is commonly in fruit by the end of May or the first week in June, while the earliest flowers of A. Rusbyi appear no earlier than mid-June, and fruit cannot be obtained before July. The pod of A. Rusbyi is nearly straight and borne on a stipe 2-5 mm. long.