Astragalus giganteus

Robust, amply leafy, with a thick, woody taproot, densely tomentulose and pilose throughout with shorter, curly or sinuous, and longer, nearly straight, spirally twisted, loosely ascending hairs up to 1.3—2.5 mm. long, the herbage silky-canescent or greenish in age, the vesture tending to turn rufous or rusty when dry; stems solitary or few together (rarely several in a clump), stout (4-9 mm. in diameter just above the root-crown), erect or stiffly ascending, (0.7) 2-6 dm. long, simple or shortly spurred below the middle; stipules herbaceous becoming dry but firm, broadly to narrowly deltoid, triangular, or lance-acuminate, 6-17 mm. long, ± semiamplexicaul-decurrent, densely silky-pilose dorsally; leaves (9) 13-35 cm. long, with stout, rather short petioles and 17-35 broadly to narrowly elliptic, ovate, oblong- or rhombic-elliptic, acute or abruptly short-acuminate, often callous- mucronulate, flat leaflets (0.7) 1-5.5 cm. long, all carinate dorsally by the prominent, pale, densely pilose midrib, the larger ones distinctly pinnate-veined; peduncles stout, erect, (0.8) 1-2.7 dm. long, either a little longer or shorter than the leaf; racemes at first rather closely (15) 20-55 (65)-flowered, the flowers ascending in bud, early horizontal and at length declined, the axis somewhat elongating, (3) 5-20 (24) cm. long in fruit; bracts lance- or linear-acuminate, 2-6 mm. long, scarious-margined, densely pilose; pedicels at first ascending, becoming arched outward or recurved and then again erect in fruit, at anthesis (1.2) 1.5-4 mm., in fruit (3) 4-9 mm. long; bracteoles 0; calyx (7.8) 10-14.7 mm. long, silky- pilose or tomentulose with pale hairs, the somewhat oblique disc 1.3-1.7 mm. deep, the deeply campanulate or subcylindric tube (6) 7-8.7 mm. long, (3) 3.3-5.1 mm. in diameter, the lance-acuminate or linear-lanceolate teeth 3-6.5 mm. long, the whole becoming papery, circumscissile at base, leaving the pod naked; petals pale yellow, immaculate; banner gently recurved through ± 45° (or further in fading), oblanceolate-spatulate or rhombic-elliptic, (14.4) 15.5-21.5 mm. long, (6.4) 6.7-10 mm. wide, shallowly notched; wings (12.4) 14.3-19.5 mm. long, the claws 6.8—9.6 mm., the linear-oblong or narrowly lanceolate, obtuse or subtruncate, nearly straight blades (7.6) 8-11.4 mm. long, 2-3.1 mm. wide; keel (11.5) 12-15.1 mm. long, the claws (7) 7.5-9 mm., the half-obovate or lunately half-elliptic blades (5.6) 5.8-7.1 mm. long, (2.2) 2.5-3.7 mm. wide, rather abruptly incurved through 85—90° to the bluntly deltoid apex; anthers (0.6) 0.65-0.9 mm. long; pod stiffly erect, sessile, plumply ovoid- or ellipsoid- acuminate, 1.5-2.5 cm. long, 8-13 mm. in diameter, slightly incurved, rounded or subtruncate at base, contracted distally into a short, triangular-acuminate, laterally compressed, unilocular beak, otherwise turgid but a little dorsiventrally compressed, flattened or shallowly sulcate dorsally (but the sinuous suture prominent), more deeply open-sulcate ventrally toward the middle, the green, fleshy, glabrous valves becoming stiffly leathery, brownish-stramineous and ultimately blackish, faintly cross-reticulate and sometimes also wrinkled lengthwise, inflexed below the beak as a complete or subcomplete septum (1.5) 2—5 mm. wide; seeds brown or black, smooth but dull, 1.9—2.6 mm. long.—Collections: 27 (o); representative. Wooton 327 (ND, NMC, NY, POM); Wooton & Standley 3424 (NMC, WIS, WS); E. J. Palmer 30,694 (MO, NY, TEX); Mueller 8324 (NY, SMU, RSA); LeSueur 679 (CAS, SMU, TEX, US); Mexia 2527 (CAS, NY); Palmer 295 (NY).

Gravel bars and banks of streams, in pine or oak forest, sometimes coming out onto open but well-watered, grassy banks, hillsides, or weedy roadsides, in volcanic or granitic soils, apparently avoiding limestones, 6000—8000 feet, local. White and Gallinas Mountains, Lincoln and Torrance Counties, New Mexico; Davis and Chinati Mountains, Jeff Davis and Presidio Counties, Texas, west slope of Sierra Madre about the headwaters of Rio Papigochic in Madera, Matachic, and Guerrero Districts, Chihuahua.—Map No. 100.—June to September, flowering exceptionally as early as mid-May.

Astragalus giganteus (giant) Wats. in Proc. Amer. Acad. 17: 370. 1882. At Fort Davis, Western Texas; Dr. V. Havard, 1881."—Holotypus (Havard 32), GH! isotypus, US.

phototypi, MO, POM!—A. texanus (of Texas) Sheld. in Minn. Bot. Stud. 1: 65. 1894, an illegitimate substitute, the supposed obstacle being a later homonym, A. giganteus (Pall.) Sheld., 1894.

Astragalus yaquianus (of Yaqui River) Wats. in Proc. Amer. Acad. 23: 270. 1888.—"On moist banks and gravelly bars of the upper Yaqui River at Guerrero, Chihuahua; Pringle (n. 1218), Sept., 1887."—Holotypus, collected 7 Sept., 1887, GH! isotypi, K, ND, NY, PH, US! phototypus, POM!—A. giganteus var. yaquianus (Wats.) Jones, Rev. Astrag. 234 (exclus. descr.). 1923. ("Yaquianus").

The giant milk-vetch, A. giganteus, is a coarse but handsome astragalus, notable for its ample, densely pilose-tomentulose foliage and well-furnished racemes of nodding, pale yellow flowers succeeded by leathery pods erect on thick, exceptionally long pedicels. The vesture of the leaves is composed of an undercoat of short, curly hairs, mixed with longer, more or less spirally twisted villi, ordinarily straight or nearly so, and spreading at a narrow angle. In Texas and New Mexico the longer hairs are relatively sparse, whereas in Chihuahua they are often, although not quite always, so closely set together as to conceal the under coat, the leaflets becoming silky-pilose. In Texas, the pod is of toughly coriaceous texture; in Mexico and New Mexico, the fruits have thinner, though still leathery walls. Differences of these sorts must be expected when the major populations are greatly isolated, but in A. giganteus the modifications seem too slight to deserve taxonomic notice.

As pointed out by Rydberg (1930, p. 539), A. yaquianus was misinterpreted by Jones. The latter’s description of A. giganteus var. yaquianus was at least partly based on the plant later described as A. Hartmanii, which differs in its much larger flower (banner over 3.5 cm. long); but the accompanying figure (Jones, 1923, Pl. 59) represents the true A. giganteus in which the typus of A. yaquianus was expressly included. The giant milk-vetch has been needlessly confused in western Texas with the ochroleucous-flowered A. mollissimus var. Coryi, endemic to the Edwards Plateau at much lower elevations and easily distinguished by its recumbent peduncles, flowers erect or ascending at anthesis, and readily deciduous pod.