Astragalus spatulatus E.Sheld.
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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
"Dry and lofty hills of the Platte towards the Rocky Mountains... "—Holotypus, labeled by Nuttall "Homalobus * caespitosus. R. Mts. Platte," BM! isotypi, some labeled "Platte to the Mts." or "High hills of the Platte," GH, K, NY, PH!
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Synonyms
Homalobus caespitosus Nutt., Astragalus caespitosus (Nutt.) A.Gray, Tragacantha caespitosa (Nutt.) Kuntze, Astragalus simplicifolius var. caespitosus (Nutt.) M.E.Jones, Astragalus simplicifolius var. spatulatus (E.Sheld.) M.E.Jones, Astragalus spatulatus var. typicus Barneby, Homalobus canescens Nutt., Homalobus brachycarpus Nutt. ex Torr. & A.Gray, Astragalus simplex Tidestr., Astragalus spatulatus var. simplex Tidestr., Homalobus uniflorus Rydb., Astragalus spatulatus var. uniflorus (Rydb.) Barneby
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Description
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Species Description - Low, dwarf, or diminutive, tufted, matted, or pulvinate, the repeatedly forking caudex beset with a thatch of persistent stipules and leaf-bases, the herbage densely strigulose with fine, straight, appressed, or some looser and sinuous, but commonly parallel and contiguous hairs up to 0.5-0.9 (1) mm. long, silvery or cinereous; stems mostly reduced to crowns, the year’s growth not exceeding 1.5 cm. in length, the internodes all concealed by imbricated stipules, together forming small tufts, prostrate mats, or domed cushions up to 3 dm. in diameter, mostly smaller; stipules papery-scarious, 2-7 mm. long, those of the short outer phyllodia the smallest, all amplexicaul and connate through at least half their length into a bidentate or subentire sheath, either all glabrous dorsally, all strigulose, or the outer ones only pubescent, the margins bristly-ciliate, at least distally; leaves all or mostly reduced to phyllodia, ± dimorphic, the lower ones spreading or decurved, 0.3-1.5 cm. long, oblanceolate or narrowly spatulate, nearly always expanded upward into a definite blade as long or longer than the petiole-like base, the later ones similar but more erect, always longer and commonly narrower, (1) 1.56 cm. long, oblanceolate or linear-oblanceolate, acute, mucronulate, or subacute, mostly simple, but a few sometimes bearing 1 (2) pairs of lateral leaflets similar in shape, the blades either fiat, or with elevated or involute margins; peduncles erect or ascending at anthesis, the outer ones of a plant often prostrate in fruit, 0.4—7 cm. long, in the most condensed states barely surpassing the stipules, but in the looser ones sometimes surpassing the longest leaf; racemes shortly but loosely, more rarely subcapitately (1) 2—9 (ll)-flowered, the axis 1—35 mm. long in fruit; bracts scarious, ovate, lanceolate, or lance-attenuate, somewhat involute, 0.5—4 (6) mm. long; pedicels ascending, straight or nearly so, at anthesis 0.3—1.7 mm., in fruit 0.7-3 mm. long, persistent until or after the fruit is ripe; bracteoles 0, rarely present and up to 3 mm. long; calyx (2.6) 3.5-5 mm. long, densely strigulose with white, partly black, or wholly black hairs, the symmetric disc (0.3) 0.4—0.6 mm. deep, the campanulate or obconic-campanulate tube 1.9—3 (3.4) mm. long, 1.5— 2.1 mm. in diameter, the erect, subulate, sometimes incurved teeth 0.5—2.3 (2.5) mm. long; petals bright pink-purple with white wing-tips, rarely cream-colored, veined and suffused with dull lilac, exceptionally white; banner recurved through ± 45°, sometimes further, (5.7) 6.5—9.5 mm. long, variable in outline, the cuneate claw expanded into an ovate, obovate, or less often rhombic-elliptic or sub- orbicular, notched blade (4.1) 4.5—6.7 mm. wide; wings (5.1) 6—8.3 mm. long, the claws (1.7) 2-3.2 mm., the lunately oblong-elliptic or -oblanceolate, obtuse blades (3.6) 4-5.8 mm. long, (1.3) 1.6-2.3 mm. wide, both incurved but the left one more strongly so and its inner margin infolded; keel (4) 4.5-6.2 mm. long, the claws (1.5) 1.9-3.2 mm., the obliquely obovate or half-circular blades 2.2-3.3 mm. long, 1.5-2.1 mm. wide, abruptly incurved through 100-135° to the rounded, rarely subporrect apex; anthers (0.25) 0.3—0.5 mm. long; pod erect or ascending at a narow angle, sessile, commonly disjointing before dehiscence but sometimes subpersistent, narrowly lanceolate, lance-oblong, or ovate in profile, (4) 5-13 mm. long, 1.5-3 (3.3) mm. in diameter, straight or a trifle incurved, rounded at base, abruptly acute or shortly acuminate at apex, cuspidate, laterally compressed and 2-sided, bicarinate by the salient sutures but more sharply so ventrally, the faces low-convex (more turgid toward the dorsal suture), the pale green, purple-tinged, or finely red-mottled valves becoming papery, brown or stramineous, smooth or reticulate toward the angles, nearly always strigulose, occasionally glabrous; dehiscence at first apical, ultimately through the base and the ventral suture; ovules (4) 6-10 (12); seeds pale ocher, olivaceous, or purplish-brown, ± rugulose, (1.4) 1.7-2.6 mm. long.
Distribution and Ecology - Hilltops, bluffs, knolls, weathered outcrops, and bare places on open hillsides or prairies, in light gravelly or sandy soils nearly always of sedimentary origin, preferring shales and sandstones, 2300-8600 feet, widespread and locally common over the northern Great Plains, from southwestern Saskatchewan, adjoining Alberta, and eastcentral Montana south through Wyoming, extreme western North and South Dakota and western Nebraska to the upper North Platte and Cache-la Poudre Rivers in northern Colorado, extending west of the Continental Divide to the Green River and Uinta Basins in northwestern Colorado, northeastern Utah, and southwestern Wyoming, and thence feebly into the Snake River drainage as far as Cassia County (Mt. Harrison), Idaho; apparently isolated on the Arkansas River in Fremont County, Colorado (Canon City).—Map No. 26.— May to July.
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Discussion
The draba milk-vetch, A. spatulatus, is variable in size of all its parts and especially so in stature. The large extreme is a loosely tufted plant with strongly developed secondary leaves, some of them often 3-, rarely 5-foliolate, with scapes surpassing the leaves, racemes of up to ten comparatively large flowers, and lanceolate pods up to 13 mm. long. On the other hand, the mat or cushion form of the species has shorter and often broader phyllodia sometimes not over 15 mm. long, depauperate racemes of tiny flowers scarcely exserted or embedded in the foliage, and short pods of plumper outline. As circumscribed by growth-habit alone, these two aspects of A. spatulatus have somewhat different areas of dispersal; the dwarfer is characteristic of the high deserts and arid plains of southern Wyoming and the Uinta Basin; the taller is chiefly a prairie plant and largely (but not exclusively) confined to lower elevations. It was this distributional factor that was decisive in favor of maintaining a var. uniflorus for the smaller type. The smallest flowers and fruits occur only on the matted or pulvinate form, and the largest on the more loosely tufted; but although the whole ranges of variation are fairly well correlated, there is a complete sequence of intergrades in each character when examined separately. The pulvinate plant is better interpreted as an immediate product of its environment. This argument gains force from observing that individuals in a population of a few hundred within a restricted area may vary considerably according to accident of situation on a hillside, the shelter of a boulder being enough to restore the normal stature. In spite of this, the populations of A. spatulatus in Utah and southern Wyoming possess individuality beyond mere nanism; and it is not difficult to imagine that they may have acquired, by accumulation of very small mutations favoring survival in a harsh climate of winds and drought, a certain genetic stability. For the present it must suffice to point out that the extreme forms of the draba milk-vetch are connected by a series of intermediates separable only by arbitrary quantitative standards of comparison, and var. uniflorus is accordingly treated here as a minor variant.
The number of ovules is very imperfectly correlated with size of the pod, although the small pod appears to mature fewer and smaller seeds. The fruit of the pulvinate form, seldom collected in fully ripe condition, perhaps falls more readily from the receptacle than is usual in the prairie type. These points deserve fuller enquiry.
The pod of A. spatulatus is almost always strigulose, but the vesture varies in density, and there are two examples of truly glabrous fruits. In one of these (Fremont County, Wyoming, Ripley & Barneby 8930, RSA) the pod was hairless in all plants collected; in the other (Duchesne County, Utah, No. 8702, RSA) it was glabrous in some plants and thinly pubescent in others.
The draba milk-vetch is always a delicately attractive little plant, but its condensed state (well illustrated, as A. simplicifolius, in King’s Report, Pl. XII, figs. 3-9) becomes spectacular during its short season of bloom. On stony hilltops and red beds in southern Wyoming, and especially on the white and tawny shales of the Uinta Basin, the mats of silvery foliage disappear beneath a veil of pink-purple blossom, with the first warm days of spring. In some places the color of the petals varies from plant to plant through tones of rose, lilac, and magenta into a deep claret-purple. Elsewhere the anthocyanic pigment blends into an ochroleucous background, turning lurid in consequence. And occasional albino forms occur.
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Objects
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Distribution
Saskatchewan Canada North America| Alberta Canada North America| Montana United States of America North America| Wyoming United States of America North America| North Dakota United States of America North America| South Dakota United States of America North America| Nebraska United States of America North America| Colorado United States of America North America| Utah United States of America North America| Idaho United States of America North America|