Astragalus Layneae

Low and rather coarse, with a deeply buried, vertical or oblique, woody primary root giving rise to slender, horizontal, indefinitely elongating, subterranean caudex-branches (rhizomes) beset with small, globose, pubescent buds (most of them inhibited but at irregular intervals along the rhizomes developing an independent root-system and aerial stems), above ground densely gray-hirsute with rather stiff, spreading or ascending, straight, incurved, or somewhat sinuous hairs up to 1-2 mm. long, the vesture sometimes composed largely of shorter, incurved hairs but some long ones always present; stems solitary or few together, slender, simple, and subterranean for a space of 1-7 cm., becoming abruptly stouter on emergence, branched or spurred at the lowest, approximate aerial nodes, the part above ground 2.5-16 cm. long, erect or nearly so, composed of several short, flexuous or zigzag internodes, the whole shorter than the longest raceme and peduncle together; stipules membranous, or the upper, spreading or deflexed ones thinly herbaceous distally, 3-10 (12) mm. long, broadly ovate-triangular to lance- acuminate, semi- or almost fully amplexicaul but free; leaves (4) 6-16 cm. long, all petioled but the upper ones shortly so, with (11) 13-21 (23) ovate, obovate, rhombic-ovate, obovate-cuneate, broadly elliptic, or suborbicular, obtuse or shallowly retuse, flat or loosely folded leaflets 5-18 (23) mm. long, dorsally carinate in age by the midrib; peduncles stout, at anthesis erect, in age often divaricate or weighed down by the fruits, 4.5-10 (14) cm. long; racemes loosely (12) 15-45- flowered, the flowers at first ascending, becoming horizontal or a little declined, the axis early elongating, (3) 5-20 (30) cm. long in fruit; bracts membranous, pallid, triangular-acuminate, lanceolate, or linear-elliptic, 2.5-6 mm. long, ultimately spreading or recurved; pedicels ascending, straight or a little arched outward, at anthesis 0.6-1.2 mm., in fruit 1.5-2.8 mm. long; bracteoles 2, usually conspicuous; calyx 6-8.8 mm. long, densely hirsute or hirsutulous with black or largely black hairs, the oblique disc (0.8) 1-2 mm. deep, the deeply or sometimes broadly campanulate tube 5-7.5 mm. long, (2.6) 3-4 (4.5) mm. in diameter, the obtusely deltoid or subulate teeth 1-2 mm. long; petals whitish with deep purple or lavender wing- and keel-tips, the banner sometimes also distally suffused or broadly margined with dull purple; banner gently recurved through ± 50°, broadly oblanceolate, rhombic-oblanceolate, or -spatulate, 12.5-17.5 (18) mm. long, 6.6-9.5 (10.2) mm. wide; wings as long or only 1 (1.5) mm. shorter, 11.8 16.5 (17.5) mm. long, the claws 5.4-9.5 (10) mm., the narrowly oblong, obtuse or obliquely truncate, nearly straight blades 6.7-9.5 mm. long, 1.9-2.7 (3) mm. wide; keel 10.4-15.4 (16.5) mm. long, the claws 5.2-9 (10) mm., the lunate or half-obovate blades 5.3—7.1 mm. long, (2.3) 2.5—3.5 mm. wide, gently incurved through 95-100° to the bluntly triangular apex; anthers (0.4) 0.450.65 (0.7) mm. long; pod loosely ascending, incurved-ascending, spreading, or rarely declined, sessile on and readily disjointing from the conical receptacle, very obliquely linear—ellipsoid, (2) 3—6.5 cm. long, 3.5—8 mm. in diameter, cuneate or acuminately tapering at base, gradually narrowed distally into a narrowly triangular-acuminate, laterally compressed, unilocular beak, either uniformly incurved into a crescent, or more commonly almost straight proximally and thereafter abruptly incurved or hooked through ? to almost a full circle, the body compressed-triquetrous or (when broad) obcompressed from the middle downward and triquetrous up to the beak, with acute ventral and rounded lateral angles, openly or sometimes narrowly sulcate dorsally, the fleshy, green or sometimes purplish, commonly red-mottled valves becoming leathery, reticulate or somewhat rugulose on the angles, villous-hirsute (hirsutulous) with straight or sinuous hairs, inflexed as a partial or complete septum 1—3.5 mm. wide; dehiscence tardy, the beak gaping; seeds pale brown, sometimes purple-speckled, pitted or wrinkled, often prismatically angled or quadrate through crowding, 2.8-4.7 mm. long.— Collections: 53 (vi); representative: Maguire & Holmgren 25,223 (NY, RSA, UTC); Eastwood & Howell 9508 (CAS, WS); C. B. Wolf 6597 (CAS, WS), 10,163,10,292 (CAS, TEX); Barneby 12,322 (CAS, NY, RSA).

Sandy flats, washes and gentle slopes or outwash fans in the foothills of desert mountains, 1500—5100 feet, with Larrea, bud-sage, or rarely in sagebrush, on granite or basalt, apparently calcifuge, locally abundant and sometimes forming extensive colonies, common and well-distributed over the Mohave Desert in southeastern California, from lower Owens Valley south to the Little San Bernardino Mountains, east into southern Nye and western Esmeralda Counties, Nevada, and (avoiding the limestones of the eastern Mohave Desert) into southern Clark County, Nevada, and adjoining Mohave County, Arizona.—Map No. 85.— March to May.

Astragalus Layneae (Mary Katherine Layne, subsequently Mrs. T. S. Brandegee, 1844— 1920, pioneer California botanist, early curator of the herbarium at CAS) Greene in Bull. Calif. Acad. Sci. 1: 156. 1885.—"Mohave Desert, Parish Brothers, 1882, No. 1273; Mrs. M. K. Layne-Curran, in the same locality, 1884."—No typus found at CAS or ND, Greene’s original material probably destroyed in the San Francisco fire. Neotypus, S. B. & W. F. Parish 1273, collected in May, 1882, on the Mohave Desert, actually at Rabbit Springs, San Bernardino County, US! isotypus, WS!—At UC there is a photograph of Mrs. Curran’s specimen from the Mohave in June, 1884.—A. malacus var. Layneae (Greene) Jones in Zoë 4: 29. 1893. Hamosa Layneae (Greene) Rydb. in Bull. Torr. Club 54: 15. 1927.

To the casual observer the stems of the Layne milk-vetch, as they spring singly or few together at intervals from sands and gravels of the desert floors and foothills, are likely to appear as separate individual plants. Careful digging, however, shows that many of them are connected underground by cords of the diameter of heavy twine, which run horizontally a few centimeters deep for indefinite distances. These cords often creep through a layer of densely compacted hardpan, so are difficult to extract unbroken. Although rootlike in form, they are in reality stem structures, homologous with the caudex-branches of the chamaephytic Astragalus, but capable of emitting adventitious rootlets, some of which develop into an independent taproot. The rhizomes are beset with gray-pubescent buds the size of small peas, most of which remain permanently inhibited; here and there one forms the point of origin of an aerial stem. Scarcely one in ten herbarium specimens of A. Layneae shows more than the annual herbaceous growth, partly subterranean, with perhaps a fragment of rhizome easily mistaken for a genuine root. Even without its characteristic rhizomes, the Layne milk-vetch is easily recognized by its coarse hirsute vesture, loose, black-hairy racemes of bicolored (purple- tipped) flowers, and long, narrow, bilocular pods. The pods vary greatly in curvature, from crescentic to annular. The less strongly incurved pod is compressed-triquetrous and narrowly grooved dorsally downward from the flattened beak, but a more pronounced or more abrupt hamate curvature results in opening of the dorsal groove and a tendency toward dorsiventral flattening.

The orientation of the ripe fruit is remarkably variable in A. Layneae. The pod most commonly ascends at a narrow angle or is incurved-ascending from a horizontally spreading base; but often it is decidedly pendulous or even abruptly deflexed. The variation or most of it can be attributed to the force of gravity rather than to any physiological peculiarity of the pedicel. When first fully formed the valves of the exceptionally long, naturally ascending pods are heavy with pulp and the peduncles are commonly bent down by their combined weight, the ripening fruit retaining its original attitude relative to the raceme-axis and appearing erect in pressed specimens. Not infrequently a stout or wiry peduncle withstands the burden of the fruits; these are then brought down individually of their own weight into a deflexed position.

The Layne milk-vetch was first collected on March 3, 1854, along the Mohave River, by Bigelow on Whipple’s Expedition (NY).