Astragalus gypsodes

Low, robust, commonly quite coarse, strigulose throughout (except the fruit) with fine, sometimes flattened, stiff, straight, appressed hairs up to 0.25-0.5 (0.7) mm. long, the herbage silvery or greenish-canescent, the leaflets pubescent on both sides, often a little more densely so above than beneath; stems several, stout, commonly purplish, (1.5) 1-3 (3.5) dm. long, ascending and radiating from a pluricipital root-crown at or up to 6 (9) cm. below soil-level, simple or few-branched at base, and often spurred at 1 or more nodes preceding the first peduncle, together forming low, bushy plants, the main axis (unless inhibited by drought) elongating beyond the topmost inflorescence and the fruits thus borne at or below the middle of the stems; stipules membranous or subherbaceous, early becoming pallid and papery, deltoid or deltoid-acuminate, 2-7 (9) mm. long, decurrent around half, or the lowest around nearly the whole stem’s circumference, the upper ones spreading or deflexed, their margins sometimes beset with a few minute processes; leaves (4) 6-18 cm. long, with short, stiff petiole and (11) 15—25 (29) elliptic, narrowly ovate-lanceolate, or rhombic-elliptic and obtuse or subacute, or (in some leaves) oblong-obovate and retuse, flat leaflets 5—20 mm. long; peduncles stout, at anthesis erect or stiffly ascending, ultimately weighed down by the heavy fruits, 3.5-10 cm. long, shorter than the leaf; racemes loosely (10) 15—30-flowered, the flowers ascending or spreading in age, the axis (2.5) 3.5—11.5 cm. long in fruit; bracts submembranous, ovate, lanceolate, or triangular- lanceolate, 2.5-6 mm. long; pedicels at anthesis ascending, 1.3-2.3 mm. long, in fruit a little thickened, usually arched outward, (1.6) 2-3.4 mm. long; bracteoles nearly always 2, setaceous or membranous; calyx 10.4-14.7 mm. long finely strigulose with white or largely black hairs, the oblique disc 1.7-2.8 mm. deep the cylindro-campanulate, purplish or reddish tube 7.3-10 mm. long 3 8-5 mm. in diameter, the subulate or lanceolate teeth (2.6) 3-5 mm. long, the whole becoming scarious, irregularly ruptured but partially marcescent; petals bright pink-purple above the pale claws, drying bluish, the keel-tip deeply maculate; banner broadly rhombic-oblanceolate, 16-23 mm., long, 7.5-12 mm. wide; wings 17.6-19.5 mm. long, the claws 8.8-10.4 mm., the lance-oblong, obtuse blades 10.2-11.7 mm. long, 2.4-3.1 mm. wide, slightly incurved in the tapering distal half; keel 15.4-18.1 mm. long, the claws 8.9-10.8 mm., the lunately half-obovate blades 7.5-9 mm. long, 3.1-3.5 mm. wide, incurved through 85-90° to the rounded apex; anthers 0.7—0.9 mm. long; pod loosely ascending or spreading (nearly always humistrate), broadly and plumply oblong-cylindroid, oblong-ellipsoid, or more narrowly cylindro- or clavate-ellipsoid, 2.5-4.5 (5) cm. long, (0.8) 1-2.1 cm. in diameter, straight or rarely a little incurved, subtruncately rounded to broadly turbinate at base, abruptly contracted at apex into a minute, conic-subulate beak, terete or a trifle compressed either laterally, dorsiventrally, or (especially when incurved) shallowly sulcate dorsally at maturity, the extremely thick, succulent, smooth and shining, glabrous, pale green but brightly purple-cheeked valves becoming alveolate-spongy and 1.7—2.3 mm. thick when ripe, the exocarp becoming stramineous or ± brownish-purple and finely reticulate-wrinkled, the endocarp inflexed as a complete septum nearly as wide as the pod’s diameter; dehiscence tardy, after falling, primarily basal and upward through the ventral suture, the seeds apparently discharged basally; ovules (41) 45-66; seeds khaki- or ocher-brown, or soot-black, sparsely pitted or wrinkled, dull, (2.9) 3.2-3.9 mm. long.—Collections: 10 (v); representative: McVaugh 8106 (DS, G, SMU, TEX); Warnock 5490 (SRSC); Ripley & Barneby 10,099 (CAS, RSA), 11,143 (CAS, NY, RSA), 11,152 (CAS, NY, RM, RSA, SMU).

Dry flats, gullied knolls, and low rolling hills, on gypsum or stiff gypseous clay soils, 2600-3900 feet, locally plentiful in the valley of the Black River near Carlsbad Cavern, southern Eddy County, New Mexico, and extreme northern Culberson and adjacent Reeves Counties, Texas.—Map No. 102.—March to May.

Astragalus gypsodes (of gypsum) Barneby in Amer. Midl. Nat. 55: 499. 1956.—"New Mexico. Gypsum flats and low gullied gypseous hills, altitude 3650 ft., 7 miles SW of White’s City, Eddy Co., 17 May, 1953, Ripley & Barneby No. 11138 ... "—Holotypus, CAS! isotypi, GH, K, NY, OKLA, POM, RM, RSA, SMU, US, WS, WTU!

The gypsum milk-vetch is a handsome, coarse plant, a member of a small, distinctive flora confined either to pure gypsum or to soils of high gypseous content. Against a background of whitish clay barrens, the plants with their silvery foliage and abundant purple flowers stand out with equal advantage in early spring as later in the season when the relatively enormous, red-cheeked, juicy fruits have reached their full size. By the middle of June, when tardier gypsophytes, such as Anulocaulis leiosolenus (Torr.) Standl. and Nama carnosum (Woot. & St.) C L. Hitchc. are beginning to dominate the scene, the pods of the astragalus are long shed; light as cork after evaporation of their succulent sap, they have been scattered by the wind.

The species is notable among the Sarcocarpi for its subcylindrical, commonly sausageshaped pod which, even though fully as thick-walled as that of A. crassicarpus, tends to fall and dehisce earlier and more readily. It differs further from var. crassicarpus in its looser, more numerously flowered racemes which are held erect at anthesis and only become humistrate when weighed down to the ground by the heavy fruits. A loosely flowered form of var. crassicarpus, local in southeastern Colorado and eastern New Mexico (already mentioned above), is less suggestive of direct passage between the species as of the probable origin of the rare and physiologically specialized A. gypsodes by mutation from some antecedent form of the widely dispersed and adaptable A. crassicarpus. The extra pair of chromosomes reported by Head (1957) must, however, isolate A. gypsodes genetically from its near kindred.