Astragalus jejunus S.Watson
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Authors
Rupert C. Barneby
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Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
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Family
Fabaceae
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Scientific Name
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Type
"...on the foothills of Bear River Valley, near Evanston, Utah [now Uinta County, Wyoming]... 279."—Holotypus, collected by Sereno Watson in August, 1869, US! isotypi, GH, NY!
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Synonyms
Tragacantha jejuna (S.Watson) Kuntze, Phaca jejuna (S.Watson) Rydb.
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Description
Species Description - Dwarf, tufted, with a stout woody taproot and strongly developed, shortly forking, suffruticulose caudex, strigulose with straight or incumbent hairs up to 0.1-0.3 mm. long, the herbage cinereous or greenish; stems (or caudex-branches) very short, beset with a thatch of persistent stipules and rigid petioles, the growth of the year 0-2 cm. long, the internodes mostly concealed by imbricated stipules, rarely a few developed and up to 5 mm. long; stipules 1.5-2.5 mm. long, at first membranous and thinly pubescent dorsally, becoming papery and glabrescent, all amplexicaul and connate into a loose sheath, the uppermost with short, deltoid free blades; leaves erect, crowded on the young shoots, 1-4 cm. long, with 9-15 (17) linear or narrowly elliptic, obtuse or subacute, thick-textured leaflets 1-5 mm. long, all ascending along the stiff, grooved rachis, the lateral ones very shortly petiolulate, at length disjointing and leaving a pitted scar, the terminal one confluent; peduncles subfiliform, 1-3.5 cm. long, erect in flower, reclinate in fruit; racemes shortly but loosely 3-7-flowered, the flowers spreading, the axis scarcely elongating, not over 1 cm. long in fruit; bracts papery-membranous, ovate-acuminate, 1-1.5 mm. long; pedicels very slender, at anthesis about 1.5 mm., in fruit 1.5-2.5 mm. long; bracteoles 0; calyx 2.3-3 mm. long, strigulose with partly black or almost all white hairs, the subsymmetric disc 0.4-0.6 mm. deep, the campanulate tube 1.5-2 mm. long, 1.3-1.7 mm. in diameter, the subulate teeth 0.61 mm. long; petals pink- or lavender-purple, the wing-tips paler or white; banner recurved through ± 70°, obovate or suborbicular above the broadly cuneate claw, 5-6.5 mm. long, 4.5-5 mm. wide; wings 4.5-6 mm. long, the claws 1.3-2 mm., the lunately oblanceolate, obtuse, more or less incurved blades 4-4.6 long, 1.4 1.8 mm. wide; keel 3.7-4.4 mm. long, the claws 1.5-2 mm., the half-obovate blades 2.5-2.9 mm. long, 1.5-1.8 mm. wide, incurved through 115-125° to the deltoid, obscurely porrect apex; anthers 0.25-0.35 mm. long; pod spreading, sessile, obliquely obovate to subglobose, beakless or nearly so, bladdery-inflated, (8) 10-17 mm. long, 7-11 mm. in diameter, with slightly convex ventral and strongly convex dorsal sutures, the papery-membranous, brightly mottled, finely strigulose valves not at all inflexed; ovules 10—14; seeds greenish-brown, purple-speckled, smooth, 1.9-2.5 mm. long.
Distribution and Ecology - Arid, windswept summits of shale, sandstone, or cobblestone bluffs, bare clay ridges, sometimes in low sagebrush, 6000—7500 feet, local but forming colonies, Green River Basin north of the Uintah Mountains and valley of the Bear River, southwestern Wyoming and immediately adjoining Utah; isolated on calcareous clay knolls in the White Pine Mountains (north of Hamilton, White Pine County), eastcentral Nevada.—Map No. 40.—May to July.
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Discussion
The starveling milk-vetch, A. jejunus, is instantly recognized by its diminutive, tufted growth-habit, imbricated, sheathing stipules, stiff leaf-rachis beset with very small, upwardly directed leaflets (the terminal one decurrent), and small, purplish flowers succeeded by small, bladdery fruits of exceptionally delicate, diaphanous texture and, as a rule, gaily mottled with reddish-purple. The petioles persistent together with the leaf-rachis as a thatch on the caudex- branches form a protective collar around the young shoots. They are of the same structure as the spines of the Eurasian Tragacanthae, but although stiff and wiry they are not truly prickly. In Wyoming and immediately adjoining Utah, A. jejunus is distributed over a very natural area centering around the Bear-Green River divide and is found commonly on shale or sandstone. The discovery of the species in Nevada, at a station lying distant some 250 miles southeast of the main range, seemed at first wholly mystifying. This type of dispersal becomes less enigmatic, however, if one considers A. limnocharis as forming part of the pattern. There are several species, e. g., Tanacetum capitatum T. & G., or vicariant pairs of related species found primarily on the high deserts of Wyoming, which reappear disjunctly in a specialized knoll environment (mostly on limestone) about the head of the Sevier in Utah; and others of bicentric dispersal in southern Utah and the calcareous highland of eastern Nevada. Leptodactylon caespitosum Nutt. is found in all three areas and must be regarded as a relic of a once more continuously dispersed flora. In Nevada A. jejunus is found on knolls of gravelly clay derived from weathered limestone, where it is associated with Leptodactylon, Artemisia pygmaea Gray, Lepidium nanum Wats. and Oxytropis oreophila Gray. There can be no question as to its spontaneous occurrence; and the material (Ripley & Barneby 9934, RSA) seems to differ in no feature of significance from the typical Wyoming form.
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Objects
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Distribution
Wyoming United States of America North America| Utah United States of America North America| Nevada United States of America North America|