Astragalus terminalis 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
"Southern Montana, on the gravelly bank of Red Rock Creek, in July, 1880, near the then terminus of the Utah and Northern Railroad; S. Watson."—Holotypus, GH! isotypus (Watson 87), K!
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Synonyms
Tium terminale (S.Watson) Rydb., Astragalus reventoides M.E.Jones, Cnemidophacos reventoides (M.E.Jones) Rydb., Astragalus terminalis var. reventoides (M.E.Jones) M.E.Jones
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Description
Species Description - Of low or moderate stature, with a thick, woody taproot and knotty, shortly forking caudex, densely strigulose (except the glabrous pod) with a coat of straight, appressed, subcontiguous hairs, the herbage silky-canescent, the leaflets sometimes a little more thinly pubescent above than beneath and greenish, the inflorescence commonly nigrescent; stems usually few, decumbent and incurved- ascending, (2.5) 5-15 (20) cm. long, composed of 2-6 flexuous or zigzag internodes up to 2-7 cm. long, the whole commonly shorter than the longest peduncle and raceme together; stipules submembranous, all shortly adnate to the petiole- base, the lowest ovate, early becoming papery-scarious, amplexicaul-decurrent around 3/4 to the whole stem’s circumference but not connate, the median and upper ones narrower, with triangular or lanceolate, erect or deflexed blades; leaves (3) 5-17 cm. long, all petioled, with (11) 13-21 oblong-obovate or ovate and truncate to deeply retuse, or linear-oblong or -elhptic and obtuse or subacute, flat or folded leaflets 3-17 mm. long; peduncles mostly incurved-ascending, 6-20 (24) cm. long, surpassing the leaf; racemes loosely (in early anthesis sometimes compactly) 7-25 (30)-flowered, the flowers nodding, the axis elongating and (1.5) 3-12 (16) cm. long in fruit; bracts membranous, ovate or lanceolate, 1-2.5 mm. long; pedicels at anthesis slender, arched outward, 0.7-1.5 mm. long, in fruit ascending, straight, thickened, 2-5 mm. long; bracteoles 0-2, minute when present; calyx 4.5-7 mm. long, densely strigulose with black or mixed black and white hairs, the subsymmetric disc 0.7-1.2 (1.4) mm. deep, the campanulate tube 3.8-5.5 mm. long, (2.4) 2.7-3.5 mm. in diameter, the triangular-subulate, obtuse teeth 0.7-1.2 (1.5) mm. long, the ventral pair commonly directed away from the broad, deeply cut ventral sinus, the whole becoming papery-scarious, fragile, ruptured but marcescent; petals white or milky-white, sometimes faintly suffused with bluish-lilac, the keel-tip always prominently maculate; banner abruptly recurved through ± 90°, ovate-cuneate, (11.2) 12.5-16.6 mm. long, 6.6-9 (11) mm. wide; wings (10.7) 12.5-15.6 mm. long, the claws (4.2) 4.5-5.4 mm., the lunately oblanceolate, obtuse or rarely obliquely emarginate blades (7.1) 8.7-11 mm. long, 2.6—4.2 mm. wide; keel 8.8—10.7 mm. long, the claws 4.3—5.3 mm., the half-obovate blades 4.5—5.7 mm. long, 2.7—3.2 mm. wide, abruptly incurved through 95—105° to the bluntly deltoid apex; anthers 0.55—0.75 mm. long; pod erect, sessile, narrowly oblong or ovate-oblong in outline, 12-17 mm. long, 3.3-6.3 mm. in diameter, nearly straight or slightly incurved, obtuse at base, contracted distally into a short, triangular, laterally compressed, cuspidate beak, otherwise obcompressed, keeled ventrally by the prominent, thick, cordlike suture, flattened or commonly openly grooved dorsally, the lateral angles plumply rounded, the green, fleshy, glabrous valves becoming stramineous, leathery, transversely rugulose-reticulate and (parallel and close to the ventral suture) wrinkled lengthwise, inflexed as a partial or nearly complete septum 0.7-1.1 mm. wide; ovules 24-36; seeds dark green suffused or thickly speckled with blackish-purple, smooth but dull, about 2.3 mm. long.
Distribution and Ecology - Stony or grassy hillsides, talus, and rocky benchlands, often in sagebrush, on limestone (or reportedly on rhyolite), 5300—10,300 feet, locally plentiful in the valleys of the Beaverhead River and Red Rock Creek in southwest Montana, south to the Pahsimeroi and Big Lost Rivers in Custer County, Idaho, south and east, becoming rare and local, along the upper Snake River from near Pocatello to the foothills of the Grand Tetons in Teton County, Wyoming.—Map. No. 64—June to August, the fruit long persisting.
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Discussion
The railhead milk-vetch is a rather variable species, especially in size of the flowers. These seem to become smaller in the mountains (as on Antelope Pass in Custer County), where the whole plant tends to become more thrifty and of lower stature, sometimes appearing acaulescent to the casual glance although never truly stemless. In the valleys and on protected banks in canyons A. terminalis is a handsome plant when in flower, with its neat, silvery foliage and rather closely flowered racemes of white or occasionally bluish-tinged flowers variegated by a prominently maculate keel-tip; but even in such sites the stems seldom surpass in length the first and longest inflorescence as measured from the fulcrant leaf to the last flower. The pod varies in outline from ovate-oblong to narrowly oblong, and the leaflets from obcordate to narrowly elliptic. These features are not correlated, however, and the admittedly "poor variety" reventoides (Jones, l. c.) characterized by relatively broad pod and leaflets seems to be no more than a minor individual variant.
The epithet reventoides was well chosen, for A. terminalis is no doubt related to A. reventus and may be described as a slender version of it, differing in its few leaflets, short calyx-teeth, and smaller, although similarly fashioned pod; and further notable among the Reventi-arrecti for its dense vesture of dolabriform hairs. First placed in Cnemidophacos, it was later transferred by Rydberg to Tium, where it was associated in sect. Arrecta with several of the bilocular Reventi-arrecti. On account of the lateral hair-attachment Jones (1923, p. 167) referred A. terminalis to his sect. Uliginosi, from which it differs importantly in its determinate, non-stoloniferous root-crown and free stipules. I have no doubt that Rydberg’s estimate of its affinities was the more nearly correct. The railhead milk-vetch was first collected June 10 and 12, 1860, in Jackson’s Hole, Wyoming, by F. V. Hayden.
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Objects
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Distribution
Idaho United States of America North America| Montana United States of America North America| Wyoming United States of America North America|