Astragalus aquilonius

Commonly robust and rather coarse, perennial but of short duration, with a stout taproot and knotty root-crown or shortly forking, indurated caudex, strigulose-villosulous with fine, loosely ascending or incumbent hairs up to 0.5—0.75 mm. long, the herbage greenish-cinereous or the young leaves subcanescent, the leaflets medially glabrescent above; stems several or numerous, decumbent or weakly assurgent, (1) 2-3.5 dm. (or in occasional precociously flowering seedlings only 0.4 dm.) long, usually purple-tinged, simple or branched from 1-3 axils preceding the first peduncle, together forming clumps of low, rounded outline; stipules 2—4 mm. long, submembranous, purplish, the lowest early becoming papery and brow- ish, mostly broader than long, amplexicaul-decurrent around ½-? -the stem, the median and upper ones narrower, with triangular or lanceolate, mostly erect blades; leaves 4-9 cm. long, all petioled but the upper ones shortly so, with (11) 15-19 (23) oval, elliptic-obovate, or broadly oblanceolate, obtuse or shallowly retuse, flat leaflets (4) 5-18 mm. long; peduncles incurved-ascending, (3) 4-6.5 cm. long, shorter than the leaf; racemes loosely 5-9-flowered, the flowers ascending and declined in age, the axis 1.5-5.5 cm. long in fruit; bracts submembranous, lanceolate or lance-acuminate, 1.5-2.5 mm. long, commonly purplish; pedicels very slender, at anthesis ascending at a wide angle, 2—4 mm. long, in fruit usually straight and divaricate but sometimes arched or twisted following the orientation of the humistrate pod; bracteoles 0-2; calyx 6.7-7.8 mm. long, loosely strigulose with white and fuscous hairs, the subsymmetric disc 0.8—1 mm. deep, the tube 3.7-3.9 mm. long, (2.2) 2.9-3.3 mm. in diameter, the slenderly subulate teeth 2.8-4 mm. long; petals greenish-white, often tinged or veined with dull lilac; banner recurved through 60-90°, ovate-cuneate or somewhat rhombic in outline, shallowly emarginate, 9.5-11 mm. long, 6-8.5 mm. wide; wings 8.6-9.5 mm. long, the claws 3.4-3.6 mm., the obliquely obovate, obtuse or obscurely emarginate blades 5.7-6.6 mm. long, 2.4-3.2 mm. wide, both incurved but the left one more strongly so and its inner margin infolded; keel 7.8-8.9 mm. long, the claws 3.5-3.8 mm., the lunately half-elliptic blades 4.7-6 mm. long, 2.1-2.8 mm. wide, incurved through 80-90° to the triangular, subacute, often obscurely porrect apex; anthers 0.55-0.65 mm. long; pod loosely spreading, declined, or (when humistrate) ascending, sessile on the slightly elevated receptacle, subsymmetrically ellipsoid or ovoid-ellipsoid, bladdery inflated, 2.5-4 cm. long, 1.3—1.7 cm. (or when pressed seemingly up to 2.2 cm.) in diameter, broadly obconic or rounded at base, contracted distally into a very short and obscure, deltoid, laterally flattened beak, otherwise a trifle obcompressed, shallowly sulcate ventrally, the thin, pale green but purple-cheeked, glabrous or strigulose valves becoming stramineous, lustrous, semitransparent, delicately cross-reticulate, the funicular flange 1-2 mm. wide; ovules (27) 30-39; seeds brown, smooth but dull, 2.4-3.1 mm. long.—Collections: 9 (i); representative: Christ 15,539, 17,752 (NY), 17,767 (ID); C. L. Hitchcock 15,694 (RSA); Ripley & Barneby 8836 (CAS, IDS, RSA, WTU).

Washes in gullied clay bluffs, steep eroded banks in canyons, and sand or gravel bars along streams, on shale, clay, or alluvial debris, sometimes in sagebrush, infrequent but locally plentiful along the upper Salmon River, from near Challis upstream about fifty miles, and (perhaps disjunctly) along the lower Lemhi River between Baker and Leadore, in Custer and Lemhi Counties, Idaho.—Map No. 119.—Late May to July.

Astragalus aquilonius (Barneby), stat. nov., based on A. Wootoni var. aquilonius (northern, the species isolated far n. of near relatives) Barneby in Amer. Midl. Nat. 41: 499. 1949.—"Idaho: four miles south of Lemhi, Lemhi Co., Hitchcock & Muhlick No. 9218."— Holotypus, WTU! isotypi, PH, RSA, WS!

The Lemhi milk-vetch, A. aquilonius, is the only species with bladdery, unilocular fruits known to occur within the watershed of the upper Salmon River. It is likely to be confused only with some member of sect. Platytropes, native to the same region, in which the greatly swollen pod is similar in exterior form but divided into two chambers by a broad septum. The species is closely related and technically similar to A. Wootoni, but at least when fully developed is a coarser, more amply leafy plant, with appreciably larger flowers (the banner 9.5-11 rather than 4.5-7.5 mm. long). Furthermore, the ovules are nearly twice as many (14-20 as opposed to 6-10 pairs) even though the average pod is only slightly larger. Vigorous individuals of A. aquilonius are likely to recall some forms of A. Douglasii, a reliably perennial species of cismontane California. However, the flowers of the two are not closely similar in fine detail of the petal-shape and -curvature, and the ordinarily 15-30-flowered raceme of A. Douglasii and its ovules, almost always in excess of 50, suffice to distinguish them. The Lemhi milk-vetch belongs to the group of species centering about A. Wootoni and A. allochrous, and represents the endemic austral element in the flora of the upper Salmon River canyon. Its range is separated from that of A. Wootoni by a distance of over 600 miles north and south.

The history of A. aquilonius goes back to the year 1915, when Jones discovered it near Baker on the Lemhi River. Jones referred (1923, p. 105) his autumnal specimens, which are depauperate, densely villosulous, and in advanced fruit, to an inclusive A. triflorus (= our A. Wootoni in great part), but the record was overlooked by Rydberg. The material from Baker has thinly pubescent pods, but plants with glabrous ovaries and fruits, not otherwise different, have been encountered more commonly since.