Monographs Details: Astragalus lyallii A.Gray
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
Family:Fabaceae
Discussion:

347.  Astragalus Lyalli

Diffuse, rather slender, with a woody taproot and at length knotty caudex, densely gray-villous throughout with extremely fine, sinuous, together with some longer, almost straight, spreading and ascending hairs up to 1-1.8 mm. long, the inflorescence commonly at least in part black- or fuscous-pubescent; stems several or numerous, decumbent and weakly ascending, (1) 1.5-4 dm. long, simple except for an occasional spur in some lower axils, but occasionally bearing a reduced peduncle, or a leaf and peduncle together (representing a suppressed branchlet) in the axil of a primary raceme; stipules thinly herbaceous becoming membranous, 3-8 mm. long, the lowest mostly ovate, the upper ones lanceolate or lance- acuminate, decurrent around ¾ or the uppermost around less than ½ the stem’s circumference, with ascending or spreading blades; leaves (3) 4—11 cm. long, the lowest petioled, the rest very shortly so or subsessile, with 11-19 mostly elliptic, linear-elliptic, or oblanceolate and acute, rarely oval and mucronate or shortly acuminate, flat or loosely folded leaflets 6-16 mm. long; peduncles numerous, the first often arising at or below the middle of the stem, erect or narrowly ascending, 1.5-6.5 cm. long, shorter than the leaf; racemes loosely (7) 10-21-flowered, the flowers early spreading and declined, the axis (2) 3.5-9 (11) cm. long in fruit; bracts subherbaceous or membranous, linear or setaceous, 1.5-4.5 mm. long; pedicels at anthesis 0.5-1 mm. long, in fruit slender, spreading or arched downward, 0.8-1.8 mm. long; bracteoles 0 (rarely a minute scale); calyx 3.8-5.6 mm. long, densely villous, the subsymmetric disc 0.2-0.6 mm. deep, the campanulate or turbinate-campanulate tube 1.6-2.5 (2.7) mm. long, 1.8-2.6 mm. in diameter, the setaceous, often curved teeth 1.7-3.4 mm. long, the whole becoming papery- membranous, ruptured, marcescent around the proximal ? or ½ of the pod; petals whitish tinged with dull lavender, the banner striate; banner recurved through ± 50°, ovate-cuneate, rather deeply notched, 5.3-7.4 (8) mm. long, 3.5-4.6 (5) mm. wide; wings 5.1-7 mm. long, the claws 1.6-2.4 mm., the obliquely elliptic- obovate, obtuse or emarginate, strongly incurved blades 3.6-5 mm. long, 1.5-2.4 mm. wide; keel 3.8-4.9 mm. long, the claws 1.7-2.6 mm., the lunately half-circular blades 2.1-2.8 mm. long, 1.4-1.9 mm. wide; anthers 0.3-0.4 (0.45) mm long; pod declined or deflexed, subsessile, the minute, glabrous, necklike stipe (0.1) 0.3-0.5 mm. long, the body subsymmetrically ellipsoid or ovoid-ellipsoid, 5-8 mm. long, (2) 2.5-3.5 mm. in diameter, cuneate at both ends, or rounded at base and cuspidate at apex, laterally and subtrigonously compressed, with low-convex lateral faces, carinate ventrally by the prominent suture, narrowly sulcate dorsally (the groove often closed), the papery, finely reticulate, villous-tomentulose valves inflexed as a complete or commonly incomplete septum 0.8—1.4 mm. wide; dehiscence tardy, after falling; ovules 4-8; seeds pale brown or olivaceous, sometimes purple-speckled, smooth but scarcely lustrous, 2.1-2.9 mm. long.—Collections: 19 (i); representative: C. L. Hitchcock 17,456 (ID, NY, RSA, WS); Piper 2683 (NY, WS); J. W. Thompson 11,620 (CAS, NY, WS, WTU), 13,703 (CAS, NY, WS, WTU); Ripley & Barneby 10,862 (CAS, RSA, WTU).

Low hills and rolling plains, in sandy or loamy soils derived from basalt, often among and taking shelter under sagebrush, 600-2200 feet, locally abundant in the Yakima and Columbia Valleys in Kittitas County, Washington, extending more rarely northeast to the Grand Coulee region in Douglas County and south to the mouth of the Snake River in Franklin County.—Map No. 156.—May to early July.

Astragalus Lyalli (David Lyall, 1817-1895, surgeon and botanist to the Canadian Boundary Survey, 1858-1861) Gray in Proc. Amer. Acad. 6: 195. 1864.—"Upper Yakima River, on the boundary between British Columbia and Washington Territory, Dr. Lyall (no. 8, ex herb. Kew.).—"Holotypus, collected in 1860, GH! isotypus, K!—Tragacantha Lyalli (Gray) O. Kze., Rev. Gen. 946. 1891. Phaca Lyalli (Gray) Piper in Contrib. U. S. Nat. Herb. 11 (Fl. Wash.): 370. 1906.

The Lyall milk-vetch is intermediate in several respects between A. Spaldingii of the preceding subsection and A. caricinus of subsect. Lentiformes, leaning toward the former in its diffuse growth-habit and free stipules and toward the latter in its loosely racemose, nodding flowers and declined, exserted pod. Although recognizable at a glance once its critical features are appreciated, A. Lyalli has often been confused with A. caricinus; the following contrasts may forestall difficulties in the future:

1. Stipules all free, semiamplexicaul-decurrent; stems weakly diffuse, equably pubescent their whole length, not more densely pubescent at base than distally; peduncles numerous, the stems floriferous upward from near the middle; pod minutely stipitate A. Lyalli

1. Stipules connate, the lower ones into a scarious, bidentate sheath, the upper ones united at base only or rarely free; stems stiffly erect and ascending in clumps, the lowest 2—4, abbreviated internodes densely white-tomentose; peduncles stiffly erect from the 2-5 uppermost leaf-axils; pod exactly sessile A. caricinus

The Lyall milk-vetch is a critical species, one of great theoretical interest. It seems quite closely related both to A. caricinus and to A. Spaldingii, yet these two astragali are different in many important features and are not closely related to each other, despite their common kinship with A. Lyalli. The origin of this curious situation is illumined by study of the dispersal patterns of the three species, as shown in the accompanying maps. It is established that A. Spaldingii is generally dispersed over the lower Columbia Basin southward from Grand Coulee except for a puzzling gap which extends over the south half of Grant and southeastern Kittitas Counties. This gap seems inexplicable in terms of probability, for there are no apparent physiographic or edaphic barriers to exclude the species. Remarkably enough, it is precisely into this gap that one can fit the main range of A. Lyalli, a species abundant in southeastern Kittitas County but known to extend north toward Grand Coulee only sporadically and south only to one station at the mouth of the Snake River. The picture is now complicated by the curious bicentric dispersal of A. caricinus. This species is most abundant along the banks of the Snake River in southwestern Idaho, reappearing in two restricted areas in eastern Washington, one near Quincy in southern Grant County, the other on and near the Rattlesnake Hills within the loop formed by the Great Bend of the Columbia. It is reasonable to interpret these outposts of A. caricinus, separated from the principal area of abundance by at least two hundred miles of mountainous terrain impassable to migration except by way of the Snake River canyon, as colonial settlements originating from water-borne seed. In Idaho A. caricinus is found on bluffs overlooking the Snake River, where every opportunity is offered for this type of seed dispersal. If such was the course of events, and A. caricinus became established in riparian habitats along the lower Columbia, it was invading the range of a related but morphologically dissimilar species, A. Spaldingii; and the stage was fortuitously set for potential introgression between the two. It seems likely that A. Lyalli represents the progeny of hybridization fixed through generations of selection; and that, having effectively replaced the pure parent strains in Kittitas County (although these still exist independently elsewhere in the Columbia Basin), it is now making some small migratory advance north and southward into the range of A. Spaldingii. The hypothesis has the merit of bringing into coherent focus three striking facts: the illogical absence of A. Spaldingii from Kittitas County; the bicentric dispersal of A. caricinus; and the morphological intermediacy of A. Lyalli.