Monographs Details: Astragalus austinae M.E.Jones
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:

353.  Astragalus Austinae

Dwarf, densely tufted, matted, or almost pulvinate, shortly caulescent or subacaulescent, with a thick, ultimately gnarled and tortuous, woody taproot and repeatedly forking, suffruticulouse caudex beset with a thatch of persistent leaf-bases, densely silvery-villous or -villosulous and often at the same time tomentulose with fine, lustrous, loosely ascending (commonly mixed with shorter, sinuous or curly hairs up to 0.65-1.3 mm. long; stems of the year almost 0 up to 11 cm. long, the internodes either all concealed by imbricated stipules or 1 or more of them developed and up to 1-2.5 (3.8) cm. long; stipules scarious, pallied, prominently nerved, 2-6.5 mm. long, all amplexicaul and connate through half to nearly their whole length into a tightly or loosely appressed sheath; leaves (0.7) 1-4 (5) cm. long, with short, thick petioles and (5) 7-13 ("17") crowded, elliptic or oblanceolate, acute or subobtuse, sessile but jointed, dorsally keeled and folded leaflets 1.5-9 mm. long; peduncles erect or ascending, or the outer ones prostrate and radiating, 1-4 (5) cm. long; racemes subumbellately 4-15-flowered, the erect and ascending flowers crowded into a dense, ovoid or subglobose head, the axis scarcely elongating, 2-10 (15) mm. long in fruit; bracts broadly scarious-margined, linear-lanceolate, involute, 3-5.5 mm. long; pedicels narrowly turbinate, 0.4-0.8 mm. long, ultimately disjointing with calyx and pod; bracteoles 0; calyx (6.6) 7-9.3 mm. long, densely villous-hirsute with white, rarely mixed with a few black hairs, the membranous, campanulate or ovoid-campanulate tube 3.3-5.3 mm. long, 2.6-3.5 mm. in diameter, the firm, narrowly subulate, commonly incurved teeth 2.9-4.6 mm. long, the whole becoming papery, a trifle tumid or inflated, marcescent around the fruit; petals whitish tinged, or the banner veined, with dull lilac, the blades of the banner and wings silvery-villosulous dorsally; banner gently recurved through ± 35°, oblanceolate or narrowly rhombic-obovate, entire or notched at apex, 8.4-11.3 mm. long, 4.2-6 mm. wide; wings 7.4—9.8 mm. long, the claws (3.3) 3.6-5.1 mm., the obliquely elliptic or obovate, obtuse, slightly incurved blades 4.1-6.2 mm. long, 1.7-2.6 mm. wide; keel 6.2-8.1 mm. long, the claws (3.3) 3.6—4.5 mm., the half-obovate or almost half-circular blades 2.9—4.2 mm. long, 1.7-2.1 mm. wide, abruptly incurved through 95-100° to the rounded, or triangular and obscurely porrect apex; anthers (0.3) 0.4-0.55 mm. long; pod ascending or spreading, included in the calyx or almost so, sessile but elevated on an obscure, slender, glabrous gynophore up to 0.5 mm. long, the body subsymmetrically oblong-ovoid, 5.5-7 mm. long, 3-3.5 mm. in diameter, rounded at base, abruptly contracted distally into a very short, erect or declined, cusplike beak, compressed-triquetrous, with low-convex or nearly flat lateral and narrower, sulcate dorsal faces, the papery, densely tomentulose valves inflexed through the lower ? of the pod as an incomplete or sometimes complete septum 0.6-1.4 mm. wide; dehiscence apical, and part-way down through the ventral suture, after falling; ovules (5) 6-8; seeds brown, smooth, dull, 1.5-1.8 mm. long.—Collections: 17 (o); representative: J. T. Howell 18,540 (CAS, RSA), 1424 (CAS); Sonne 673 (NY); Hitchcock & Martin 5478 (NA, WS, WTU); Train 4468 (NA, NY).

Dry exposed ridges and open gravelly slopes near and above timber line, 8800-10,500 feet, rare and local, known only from five summits of the Sierra Nevada enclosing Lake Tahoe to the north, west, and south; Mt. Stanford and Mt. Lola, Nevada County, Tinker’s Knob, Placer County, and Mt. Tallac, Eldorado County, California; Mt. Rose, Washoe County, Nevada.—Map No. 158.—July to September.

Astragalus Austinae (Rebecca Merritt Austin, 1832-1919) Gray ap. Brew. & Wats., Bot. Calif. 1: 156. 1876.—"Summit of Mount Stanford (Castle Peak), Nevada Co., at 9000 feet, Lemmon "—Holotypus, Lemmon in 1875, GH! presumed isotypus, Lemmon 73 in 1875, NY! —Tragacantha Austinae (Gray) O. Kze., Rev. Gen. 943. 1891.

The Austin milk-vetch is an unusually pretty and interesting species, remarkable for its densely tufted or cushion growth-form, headlike racemes little or not exserted from the foliage, scarious, boat-shaped bracts, pubescent petals, and small pod included or nearly so within the marcescent and slightly inflated calyx. Although the small pod is reminiscent of that of A. Spaldingii and the pubescent petals recall A. tyghensis, the similarities are interpreted as the outcome of parallel but independent evolutionary processes. The close affinity of A. Austinae lies not with the genuine Chaetodontes but with A. Andersonii, found within only a few miles but at much lower elevations. The similarity of the two species is most easily observed in the rather unusual specimens of A. Austinae in which the stems (especially those from the outer ranks in large, mature plants) have become more or less strongly caulescent in their struggle outward toward the light. Isolated from the mother plant, stems of this sort are not easy to distinguish at anthesis from A. Andersonii except for the hairy petals and few ovules. The short, few-ovulate pod is distinct, but is essentially like that of A. Andersonii in structure and compression.