Astragalus asclepiadoides

  • Title

    Astragalus asclepiadoides

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus asclepiadoides M.E.Jones

  • Description

    178. Astragalus asclepiadoides

    Stout, caulescent herbs of singular appearance, glabrous except for the bracts, pedicels, and calyx, the large, simple, subsessile leaf-blades leathery and glaucous; stems solitary or more often several or numerous, erect and ascending in clumps from a thick, pluricipital root-crown at or just below soil-level, 0.7-3.5 (4) dm. long, simple or nearly so, leafless at the lower nodes, but the base often clothed in a thatch of imbricated stipules; stipules membranous, pale, or early becoming so, ovate or deltoid, 2—15 mm. long, shortly adnate to the margins of the subobsolete petiole, decurrent on the stem, amplexicaul around 1/3 to nearly the whole stem’s circumference, free; leaves crowded, loosely imbricated, reduced to a subsessile, broadly ovate to suborbicular, obtuse or shallowly retuse and mucronulate leaflet 1.5—4.5 cm. long, prominently pinnate-nerved beneath; peduncles stout, erect, 1-4.5 cm. long; racemes rather closely 5-12-flowered, the flowers narrowly ascending, usually only 1-3 of the lowest maturing fruit, the axis little elongating, 0.4-2.5 cm. long in fruit; bracts membranous, ovate or ovate-acuminate, 1-3 (5) mm. long; pedicels ascending, at anthesis 1-2 mm. long, in fruit greatly thickened, 2-4 mm. long; bracteoles commonly 2, at or below the base of the calyx; calyx 10.5-15 mm. long, thinly strigulose with short, black hairs, the obliquely obconic disc 1.3-2.5 (3) mm. deep, the cylindric, membranous and sometimes turgid tube 8.8-11.4 mm. long, 2.8-4.6 mm. in diameter, the orifice oblique, the subulate teeth 1.3-3.5 mm. long, the whole becoming papery, marcescent unruptured; petals greenish-yellow with pale wing-tips and luridly purple-tipped keel, or all dull purple with pale or white wing-tips; banner gently recurved through ± 30°, broadly oblanceolate or somewhat rhombically angled in the distal 1/3, notched, 17-23.5 mm. long, 6.8-10 mm. wide; wings 16.8-21 mm. long, the claws 10—12 mm., the narrowly oblong or lance-oblong, obtuse, nearly straight blades 7.3-10.4 mm. long, 1.9-3.1 mm. wide; keel 14.2-18.5 mm. long, the claws 9—12 mm., the lunate blades 5.7—8.2 mm. long, 2.7—3.3 mm. wide, gently incurved through 80—100° to the rounded apex; anthers 0.6—0.9 (1) mm. long; pod erect, stipitate, the stout, clavate stipe 1—2.1 cm. long, the body broadly and subsymmetrically ovoid or ovoid-ellipsoid, inflated but scarcely bladdery, (2) 2.5-3.5 cm. long, 1.1-1.6 cm. in diameter, subtruncate or rarely cuneately contracted at base, abruptly contracted distally into a conic and cuspidate, slightly compressed beak, otherwise subterete but shallowly and openly sulcate ventrally, the somewhat fleshy, pale green but purple-speckled, glabrous valves becoming leathery or stiffly papery, stramineous, faintly reticulate, inflexed as a very narrow septum 0.5-1 mm. wide, the ventral suture also inwardly produced as a flange 0.7-1.2 mm. wide; seeds pale brown, smooth, dull, 2.2-3 mm. long. Collections: 30 (viii); representative: Jones 5455 (MO, NY, POM, WIS); W. A. Weber 3733 (CAS, TEX, WS), 7482 (CAS, SMU); Ripley & Barneby 4703 (CAS, NY, RSA); Barneby 12,690 (CAS, NY, RSA).

    Adobe clay flats, gullied knolls, and gulches in barren clay or cobblestone-clay hills, blufls, and badlands, commonly associated with Atriplex species in saline soils derived from weathered shales and standstones, 4100-6000 feet, not uncommon and locally plentiful in the basins of the Green and Grand Rivers in eastern Utah and western Colorado, from the Uinta Basin to the San Rafael Swell, east around the foot of Tavaputs Escarpment to the lower Grand and Gunnison Rivers; also somewhat isolated in the Sevier Valley near Gunnison, Sanpete County, Utah. Map. No. 71.—May and June, the fruit long persisting.

    Astragalus asclepiadojdes (resembling, in the leathery, glaucous foliage, Asclepias cryptoceras Wats.) Jones in Zoë 2: 238. 1891.-"... on sand bars along the Price River, in Eastern Utah, elevation 5,000 feet... first collected by me... in... in September, 1888, and also at Green River, Utah ... on June 21, 1889."—Holotypus, collected June 21, 1889 at Cisco, Grand County, POM! paratypus, from Price, in 1888, POM!—Jonesiella asclepiadoides (Jones) Rydb. in Bull. Torr. Club 32: 661. 1905.

    The milkweed milk-vetch, A. asclepiadoides, is one of the pre-eminently singular monotypes in the genus. Its most remarkable feature is the reduction of the leaf to a simple, leathery blade of broadly ovate or circular outline, which appears sessile on the stem but is in reality jointed to a subobsolete petiole and evidently represents the terminal leaflet of the primordial imparipinnate leaf. A similar modification has occurred in the Armeno-Caucasian A. Candolleanus Bss., although in this instance the petiole remains fully developed; and the closely related A. latifolius Lamk., with its three- or at best few-foliolate leaves shows an intermediate stage of evolution from the ordinary pinnate leaf of sect. Proselius Bge. In A. asclepiadoides no such intermediate species has survived to point to any near relatives in the genus, and its affinities remain very doubtful. Jones assumed a relationship to the rare and remarkable A. sabulosus, which has, indeed, uncommonly few and large leaflets, and inhabits, moreover, a similar environment; but this differs so greatly in its nodding, sessile pod that the assumption is not justified. Furthermore, A. sabulosus is seleniferous, whereas A. asclepiadoides, even though native to soils often rich in selenium, absorbs only insignificant amounts of the element and lacks the characteristic odor of the selenium-converter. The differences in physiology, together with the morphological disparities, provide a strong case against combining the Pattersoniani and Sabulosi with A. asclepiadoides into Jonesiella Rydb. or the even more inclusive sect. Preussii Jones. An imaginary plant combining the flowers and fruits of A. asclepiadoides with leaves of a common pinnate type would be most nearly suggestive of sect. Reventi-arrecti, but no particular species of that group can be singled out as related to the milk-weed milk-vetch in any near sense. An affinity in the same direction, and equally remote, has been suggested for the equally curious monotype A. ampullarius. It seems possible that both have arisen from progenitors of the A. eremiticus type. The deeply buried root-crown and connate stipules of A. ampullarius exclude the species readily from sect. Pachyphyllus, although the pod is similar to that of A. asclepiadoides in most technical details.

    The milkweed milk-vetch is comparatively common on the upper Price and San Rafael Rivers, and again along the lower Grand River and principal tributaries, but it has seldom been collected on the intervening deserts of the lower Green River in Utah and is rare on the floor of the Uinta Basin. The variation in flower-color, from a greenish-yellow to dull, lurid purple, usually with contrasting pallid or whitish wing-tips, seems to follow no geographic pattern. In other respects the species is virtually monomorphic.