Astragalus Hamiltoni
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Title
Astragalus Hamiltoni
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Authors
Rupert C. Barneby
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Scientific Name
Astragalus hamiltonii Ced.Porter
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Description
66. Astragalus Hamiltoni
Closely resembling robust states of A. lonchocarpus, densely strigulose with filiform or somewhat flattened, appressed hairs up to 0.4-0.6 mm. long, the herbage ± silvery-canescent, the leaflets more densely pubescent above than beneath; stems several, erect and ascending in clumps, 2.5-4 dm. long, leafless and fistula toward the base, branched or spurred at 1-4 nodes preceding the first peduncle, sometimes bearing a short spur inserted between the first peduncle and its subtending leaf; stipules firm, early becoming papery and brownish, 1.5-9.5 mm. long, the large lower ones ovate, strongly adnate to (or united behind) the vestigial petiole, decurrent around ½ to the whole stem’s circumference (exceptionally very shortly connate), the median and upper ones progressively smaller, triangular to deltoid-acuminate, the spreading blades either glabrous or pubescent dorsally; leaves 3-7 cm. long, at least some of the lower ones pinnate, with 1-2 (3) pairs of often irregularly inserted, oblong-oblanceolate, obtuse lateral leaflets 1-2.5 cm. long, the terminal one longer and often a trifle broader than the last pair and 1-3.8 cm. long, either obtuse or retuse, tapering into and continuous with the rachis, the upper leaves mostly reduced to a simple, shortly petiolate blade of similar outline; peduncles erect and incurved-ascending, 2.5-15.5 cm. long, the vigorous lower ones far surpassing the leaf; racemes loosely (6) 10-30 (35)- flowered, the axis (1) 2.5-11 cm. long in fruit; bracts firmly papery, triangular- acuminate, 1-2.5 mm. long; pedicels densely and rather loosely strigulose, at anthesis 1.2-2.5 mm., in fruit arched out- and downward, thickened, 1.2-3 mm. long; bracteoles 0-2, commonly present; calyx 8.2-11.5 mm. long, strigulose with white and rarely a few black hairs, the strongly oblique disc 0.9-1.7 mm. deep, the reddish or pallid, deeply campanulate tube gibbous dorsally behind the pedicel, 6.5 9.2 mm. long, 4-5.5 mm. in diameter, the ventral pair of teeth triangular-subulate, 1.7-2.6 mm.long, the rest shorter, closely approximate, the orifice oblique; petals ochroleucous, concolorous; banner recurved through 45° (further in withering), broadly rhombic-oblanceolate, notched, 20-24 mm. long, 7.4-12 mm. wide; wings 17.1-22.5 mm. long, the claws 8.5-10.8 mm., the linear, lanceolate, or narrowly elliptic, obtuse, nearly straight blades 10-12.7 mm. long, 2-3.8 mm. wide; keel 13.7—16.6 mm. long, the claws 8.1—10.5 mm., the half-obovate blades 6.2—7.7 mm. long, 3-3.7 mm. wide, abruptly incurved through 90° to the bluntly deltoid apex; anthers (0.65) 0.75-1.1 mm. long; pod pendulous, stipitate, the slender, strigulose stipe 9.5-12 mm. long, the body narrowly ellipsoid, 2.5-3.5 cm. long, 5.5-7.5 mm. in diameter, cuneately tapering at both ends, cuspidate at apex, straight or nearly so, obcompressed, low-convex ventrally and carinate by the prominent, thick suture, flattened dorsally, the green, thinly fleshy valves becoming papery and brownish, finely cross-reticulate and wrinkled lengthwise, sparsely strigulose in the lower half but glabrescent or glabrous distally; ovules 16-22; seeds unknown.—Collections: 5 (i); representative: Barneby 12,711 (CAS, K, NY, POM, RSA, UTC); B. Untermann 15a (BRY).
Gullied banks and ridges, in soft sandy clay soil overlying sandstone, with Utah juniper, ± 5200-5400 feet, locally plentiful but known only from Asphalt Ridge at points ± 5 miles southwest and due west of Vernal, Uintah County, Utah. —Map No. 23. May and June.
Astragalus Hamiltoni (the discoverer) C. L. Porter in Rhodora 54: 159. 1952. Type. J. W. Hamilton & O. A. Beath, s. n., on the Wahsatch formation, 5 miles south of Vernal, Uintah County, Utah, May 24, 1950 ... Paratype: C. L. Porter 5313, from the same locality, June 3, 1950."—Holotypus, RM! isotypus, GH! paratypi, GH, MO, NY, RM, SMU, TEX!
The Hamilton milk-vetch is poorly distinguished from A. lonchocarpus. Stipules, flowers, except for small differences in size, and pods are almost identical in the two species. The few broad leaflets, reduced in number but scarcely in size upward along the stems, create a strong and lasting impression of distinctness, but the modification in the foliage is hardly enough to counterbalance similarities in other organs. The species is known at present from a very small area, possibly from only two populations, so that a verdict on its taxonomic status is probably premature. The main range of A. lonchocarpus lies south of Tavaputs Escarpment, but it is known to occur in one place on the White River within the Uintah Basin about 60 miles east of Vernal. Forms intermediate in leaf characters are to be sought in the intervening territory.
The Torrey and Kew herbaria have possessed specimens of A. Hamiltoni for well over a century, collected on the Uintah River by Fremont on June 5, 1844. It must have formed part of the "rich addition to our botanical collection," mentioned in Fremont’s Report (1854, p. 279) as having been obtained in transit between the old Fort Uintah and Ashley’s Fork, that is, in the badlands lying between Vernal and Fort Duchesne.