Astragalus allochrous

Low, commonly coarse, biennial or short-lived perennial, usually flowering and often perishing the first summer, strigulose nearly throughout with straight or mostly straight, appressed or subappressed hairs up to 0.45-0.7 mm. long, the herbage green or when young cinereous, the leaflets either pubescent or glabrous above; stems several or many, ascending and radiating from the shortly forking root-crown to form low, rounded clumps, the principal ones (1) 1.5-5 dm. long, simple or commonly branched or spurred at 1-several nodes preceding the first peduncle, purplish at base; stipules thinly herbaceous or submembranous, the lowest early becoming papery, triangular or ovate-acuminate, 1.5-7 mm. long, decurrent around half, or the lowest around the whole stem’s circumference, the margins of the latter ordinarily free, rarely very shortly and obscurely connate (but then more strongly adnate than connate); leaves 4-10 mm. long, the uppermost either shortly petioled or subsessile, with (9) 11-21 oblong-obovate, oblanceolate and obtuse or retuse, or (especially in some upper leaves) elliptic or narrowly oblong-elliptic and either obtuse and mucronulate or acute, flat or loosely folded leaflets (4) 6-21 mm. long; peduncles incurved-ascending, 3-9 (11) cm. long, commonly shorter, rarely surpassing the leaf; racemes loosely 10-20 (30)-flowered, the flowers ascending at anthesis, the axis (1.5) 3.5-12 cm. long in fruit; bracts submembranous, pallid or purplish, ovate or lanceolate, 1.2-2.5 mm. long; pedicels at anthesis ascending, straight, 1-2 mm. long, in fruit arched outward, a trifle thickened, 2-4 mm. long, persistent; bracteoles 2, often minute, attached at or below base of the calyx; calyx (3.6) 4.1-5.7 mm. long, strigulose with white or mixed black and white hairs, the subsymmetric disc 0.5-1.1 mm. deep, the campanulate or turbinate-campanulate tube 2.4-3.5 mm. long, 1.9-3.6 mm. in diameter, the lance-subulate teeth (1.1) 1.6-2.5 mm. long, the ventral pair often longest, the whole becoming papery-scarious, ruptured, marcescent; petals pink- or reddish-purple, drying violet; banner recurved through ± 50°, broadly ovate -cuneate or obcordate, 7.2-9.4 mm. long, (4.9) 5.5-7.2 mm. wide; wings 6.6-8.3 mm. long, the claws 2.3-3.1 mm., the obliquely oblong-obovate, broadly obtuse or undulate-erose blades 4.7-5.7 mm. long, 22-2.1 mm. wide, both incurved but the left one more abruptly and further than the right; keel 6.2-7.5 mm. long, the claws 2.5-3.2 mm., the obliquely triangular blades 3.8-4.5 mm. long, 2.1-2.5 mm. wide, incurved through ± 95° to the blunt or subacute, slightly porrect apex; anthers 0.45-0.55 (0.6) mm. long; pod loosely spreading or declined, those of some outer stems often humistrate and ascending, sessile on the slightly elevated receptacle and readily deciduous, very obliquely ellipsoid or half-ellipsoid, bladdery-inflated, (2) 2.5-4 (4.5) cm. long, 1-1.7 (or when pressed apparently to 2) cm. in diameter, obconic at base, contracted ± 3-6 mm. below the apex into a triangular, compressed, slightly incurved beak, the ventral suture straight or nearly so, the dorsal one strongly convex, the thin, pale green or purple-cheeked, finely strigulose valves becoming papery-diaphanous, stramineous, lustrous, delicately cross-reticulate, not inflexed, the funicular flange 0.4-0.8 mm. wide; dehiscence apical, after falling; ovules (10) 14-21; seeds brown, ocher- or greenish-brown, sometimes purple-speckled, nearly smooth or irregularly pitted, dull, 2.6-3.2 mm. long.—Collections: 61 (viii); representative: Peebles 6862 (ARIZ, NY); Barneby 12,624 (CAS, RSA); Jones (from Skull Valley) in 1903 (CAS, NY, POM, TEX); Metcalf 34 (ND, NMC, NY); Bigelow, Mex. Bound. Surv. 261 (NY)\ Ripley & Barneby 4210, 11,172,11,182 (CAS, RSA).

Plains, foothills, and open valleys, on light sandy or gravelly soils of various origin and composition but apparently not or seldom on calcareous bedrock, in desert-grassland, scattered scrub-oak or juniper forest, rarely on dunes, (reportedly 1500) 2000-6200, exceptionally up to 7500 feet, common and locally abundant nearly throughout the Gila River drainage system in central and southeastern Arizona and southwestern New Mexico, extending sparingly northwest to the Big Williams River in Yavapai County, north in New Mexico to Acomita in Valencia County, and east across the Black Range to the lower Rio Grande Valley in New Mexico and extreme western trans-Pecos Texas; to be expected in adjoining Mexico.—Map No. 118.—April to July, sometimes again in fall.

Astragalus allochrous (of different color, the petals purple as contrasted with those of A. Douglasii) Gray in Proc. Amer. Acad. 13: 366. 1878.—"Near Wickenburg, Arizona, Dr. E. Palmer, 1876."—Holotypus (Palmer 588 in 1876), GH! isotypi, MO ("Hassayampa Valley"), NY (2 sheets), US!—Phaca allochroa (Gray) Rydb., Fl. Rocky Mts. 1063. 1917.

The Hassayampa milk-vetch, A. allochrous, is closely related to A. Wootoni, differing ideally if not quite consistently in its more robust growth-habit, slightly larger, usually more numerous and always purple flowers, and strongly oblique, half-ellipsoid pods contracted distally into a well-defined beak. The flowers in A. Wootoni vary from whitish to purple, but the anthocyanin when present is commonly of a more vinous, reddish, or amethystine tint in the living state; the racemes are seldom over 10-flowered; and the pod is subsymmetrically ellipsoid or subglobose and beakless or nearly so. By virtue of a wider climatic and altitudinal tolerance A. Wootoni is the more widely dispersed of the two species, but they are sympatric over a large part of southern Arizona and New Mexico. In the Gila Basin proper, where A. Wootoni seems to be commoner on the open plains and A. allochrous more abundant in the foothills, the species are almost always clearly distinguished. In the Rio Grande Valley, and along the Mogollon Escarpment in the Colorado drainage, occasional populations or samples of perhaps polymorphic colonies are difficult to assign to either species, some combining the small, whitish flower of A. Wootoni with an oblique pod, others a larger, purple flower with symmetric or subsymmetric pod. The great number of specimens collected during the past half-century in Mesilla Valley between Las Cruces and El Paso includes typical material of both species, but also many intermediate forms suggestive of a long period of introgressive hybridization. I have, however, no positive evidence bearing on this point. Judging from these gatherings alone (and occasional but truly rare examples from Arizona) I might be persuaded that only one variable species was involved. To the north, east, and west of A. allochrous, however, A. Wootoni retains a consistent identity. The relatively numerous flowers and often broad leaflets of the Hassayampa milk-vetch are reminiscent of A. Douglasii, with which Gray at first contrasted it; but the latter is Californian, strongly perennial, and differs greatly in the finer details of petal-shape and -proportion, as well as in the easily observed ochroleucous flowers and much more numerous ovules and seeds.

Variation in A. allochrous, other than already described in relation to A. Wootoni, is scarcely noticeable. In Arizona and immediately adjoining New Mexico the leaflets are pubescent on both sides, whereas farther northward and eastward in New Mexico and Texas the upper surface is glabrous. Although the geographic segregation of the two forms is (to my present knowledge) perfect, they differ too little to be considered as more than minor variants.

From time to time in the past A. allochrous has been reported as ranging north to Albuquerque in New Mexico and east to the White Sands, and even into Utah and Colorado. No corresponding specimens have been encountered, and the burden of confirmation must be laid on future exploration. There can be little doubt that the species extends south into Chihuahua, where it may have been collected long ago by the botanists of the Mexican Boundary Survey.