Astragalus sabulonum

Low, diffuse annuals, diminutive or comparatively coarse and leafy, with a filiform or slender taproot, the stems sometimes becoming indurated at base late in the season but the root apparently never persisting into a second year, the stems and herbage villous-hirsutulous with fine, spreading, ascending, or curly and entangled hairs up to 0.5-1 mm. long, usually densely so and silky- or hoary- canescent, sometimes thinly so and greenish, the leaflets bicolored, yellowish-green beneath the vesture and often medially glabrescent above; stems 1-3 from the cotyledons, 1.5-26 cm. long, in small individuals solitary and simple, either erect or decumbent, when more vigorous branching from the lower nodes, the branches incurved-ascending or prostrate with ascending tips, simple and zigzag distally, usually purple-tinged; stipules subherbacous, often purplish, becoming brownish and papery, deltoid or deltoid-acuminate, 1.5-4 mm. long, not more than semi-amplexicaul-decurrent, the blades often squarrose; leaves 1.5-6.5 cm. long, all petioled, with (5) 9-15 oblanceolate, oblong, or rarely obovate-cuneate, retuse, truncate, or obtuse, flat or folded leaflets (2) 4-13 mm. long; peduncles incurved- ascending, 1-3 (4) cm. long; racemes loosely 2-5 (7)-flowered, the flowers spreading or loosely ascending at anthesis, declined thereafter, the axis a little elongating, 0.3-2.5 cm. long in fruit; bracts submembranous, linear-setaceous or lanceolate, 1-2.5 mm. long; pedicels at anthesis 0.8-1.2 mm. long, in fruit somewhat thickened, arched outward, 1.2-2 mm. long, persistent; bracteoles 0; calyx 3.3-6.2 mm. long, white- or rarely partly black-hirsutulous, the disc about 0.5 mm. deep, the tube 1.6-2.4 mm. long, (1.8) 2-2.7 mm. in diameter, the subulate, often setaceous-tipped teeth 1.7-3.5 mm. long, the whole becoming papery, ruptured, marcescent; petals ochroleucous tinged or veined with lilac or dull purple, more rarely violet-purple with a pale, striate eye in the banner; banner recurved through 50-70°, 5.2-1.2 mm. long, the shortly cuneate claw abruptly expanded into an ovate, obovate or suborbicular, obtuse or obscurely emarginate blade 3.8-5.4 mm. wide; wings 5.1-6.1 mm. long (sometimes a trifle longer than the banner), the claws 1.8-2.6 mm., the obliquely obovate, obtuse or subemarginate, slightly incurved blades 4.2-5.3 mm. long, 1.8-2.4 mm. wide; keel (5) 5.4-6.5 mm. long, the claws 2-2.6 mm., the broadly lunate blades (3) 3.2-4.2 mm. long, (1.8) 2-2.3 mm. wide, incurved through 100-120° to the rather narrowly triangular, erect or slightly porrect apex; anthers (0.35) 0.4—0.5 mm. long; pod spreading or declined (often humistrate), sessile, obliquely ovoid, oblong-ovoid, or ovoid-ellipsoid, turgid or somewhat inflated but not bladdery, 9-17 (20) mm. long, (4) 5-8 (11) mm. in diameter, either lunately incurved or sometimes abruptly hooked toward the middle, somewhat obcompressed at the cuneate or rounded base and there often sulcate ventrally, contracted distally into a short, deltoid beak, either rounded or shallowly and openly sulcate dorsally, the thinly fleshy, green or purple-cheeked, sometimes obscurely red-mottled, thinly to densely white-hirsutulous or almost hirsute valves becoming leathery or stiffly papery, brownish or stramineous, not inflexed; dehiscence apical, through the gaping beak, after falling; ovules 10—19; seeds brown, sometimes purple-dotted, lustrous but irregularly pitted, 2—2.5 mm. long.—Collections: 40 (x); representative: A. & R. Nelson 3307 (NY, SMU, WS); Keck & al. 6190 (NY); Eastwood & Howell 9471 (CAS, WS); Ripley & Barneby 2871, 8379 (CAS, RSA); Holmgren 3221 (NY, RSA, TEX, WS, WTU); Barneby 12,666 (CAS, NY, RSA); MacDougal 87 (NY).

Sandy flats, dunes, sandy or gravelly washes, and pockets in gullied clay hills, widespread and locally plentiful in the Colorado Basin and southern Great Basin, between 2000 and 6500 feet, from the lower Little Colorado River in Coconino County, Arizona, north to the San Rafael Swell, Emery County, Utah, and east up the San Juan River into northwestern San Juan County, New Mexico, west into northern Mohave County, Arizona, and thence north through southern Nevada to southern Nye and Esmeralda Counties; also disjunctly, from 350 feet below to about 600 feet above sea level, locally plentiful in Larrea desert around the Salton Sea, from near Mecca and Indio in interior Riverside County, California, south through Imperial County to extreme northwestern Sonora (and probably adjoining Baja California).—Map No. 123—February to July, or in southeastern California, November to April.

Astragalus sabulonum (of coarse sands and gravels) Gray in Proc. Amer. Acad. 13: 368. 1878.—"Southeastern border of Nevada, near the confluence of Muddy River with the Rio Virgen, on sandy ridges, Dr. Palmer, 1877."—Holotypus (from "Muddy River at St. Thomas," Palmer 110 in 1877), GH! isotypi, K, MO, NY (2 sheets) US!—Phaca sabulonum (Gray) Rydb. in Bull. Torr. Club 40: 47. 1913.

Astragalus virgineus (of the Virgin River) Sheld. ap. Cov. in Contrib. U. S. Nat. Herb. 4: 88. 1893.—‘Type specimen in the United States National Herbarium, No. 1910, Death Valley Expedition; collected May 6, 1891, below St. George, in the Valley of the Virgin River, Lincoln County, Nevada [acc. to Cov., op. cit. p. 276, below St. Thomas, Nevada, i.e., on the lower Virgin River in the present Clark County], by Vernon Bailey."—Holotypus, US!

Phaca arenicola (dwelling in sand) Rydb. in N. Amer. Fl. 24: 356. 1929.—"Type collected in sand at Mecca, Salton Basin, Southern California, Feb. 28, 1913, Parish 8467 ... "—Holotypus, NY! isotypus, NY!

Phaca lerdoensis (of Colonia Lerdo) Rydb. in N. Amer. Fl. 24: 356. 1929.—Type collected at Colonia Lerdo, northern Sonora, February, 1904, D. T. Macdougal... "—Holotypus, NY!

The gravel milk-vetch, A. sabulonum, is quite unusual in the section because of its small, tumescent but not really inflated pod with decidedly juicy, inwardly filamentous valves drying out to a leathery or stiffly papery texture. The affinities of the species are nevertheless apparent by way of A. pubentissimus, geographically vicariant and often confused with A. sabulonum, but differing in its longer petals further exserted from the calyx and in the pod which is equally or even more strongly oblique and incurved but bladdery, papery-membranous, and shaggy- pilose with much longer, lustrous hairs. Occasional specimens of A. sabulonum have been misidentified as A. desperatus, a reliably perennial species of the Colorado Basin, which is commonly subacaulescent and bears papery pods similar to those of A. pubentissimus but mostly smaller and hirsute with divergent hairs seated on a minutely bulbous base.

Other notable features of A. sabulonum are its bicentric dispersal and enormous altitudinal tolerance. Above 2000 feet in the interior deserts, from southern Nevada east and northward, the seeds germinate in spring and the season of active growth lasts from about the end of February or April to June or early July. The greater part of the life-cycle takes place in the period of long days and short nights after the spring equinox. Near and below sea level in the Salton Basin the plants behave as winter annuals, the seed germinates in late fall or winter, and the active growth is spaced over the short days and long nights before and after the winter solstice. It is astonishing that no perceptible modification in form has accompanied the physiological adaptation to environments so substantially different; except that the plants in the Colorado Desert tend to be more robust and coarsely leafy and to become indurated at base early in the year (sometimes, as in the typus of Phaca arenicola, appearing biennial in consequence), I can make no distinction between the plants in the two main areas of dispersal. Along the San Juan River eastward from Monument Valley, the average plant of A. sabulonum is less densely and a trifle more shortly pubescent than elsewhere, but the difference in vesture is really negligible.

The type-collections of A. sabulonum and A. virgineus came from nearly the same spot and are essentially identical. That of P. lerdoensis was supposed to differ from A. sabulonum in its decumbent branches and villous vesture, features characteristic of the species. The differential characters of P. arenicola were a "suffruticulose," in reality only slightly indurated base, and inconsiderable differences in length of the inflorescence and shape of the leaflets. Neither has any claim to taxonomic recognition.