Astragalus microcystis A.Gray
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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
"Interior of Washington Territory, Fort Colville to the Rocky Mountains, Dr. Lyall (ex herb. Kew. no. 4, 5, 6)."—Lectotypus, Lyall 5, from the Columbia Valley between Fort Colville and Fort Shepherd, in 1860, GH! isotypus, K! paratypi (Lyall 4 & 6), GH, K
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Synonyms
Tragacantha microcystis (A.Gray) Kuntze, Phaca microcystis (A.Gray) Rydb.
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Description
Species Description - Low, slender, diffuse or loosely tufted, with a slender or sometimes greatly thickened and trunklike taproot (up to 1.5 cm. in diameter) and loosely forking caudex, strigose-pilosulous with sinous or nearly straight, subappressed, incumbent, or spreading hairs up to 0.3—0.6 (0.7) mm. long, the stems commonly strigulose and the leaves more loosely pubescent, the herbage green or greenish-cinereous, the leaflets medially glabrescent or glabrous above; stems many, decumbent and ascending, 0.5—4 (5) dm. long, purplish at base, branched or shortly spurred at the lower and median axils, the branchlets sometimes paired with a peduncle upward; stipules 1-5 (6) mm. long, dimorphic, the lower ones amplexicaul and connate into a papery, often nigrescent, truncate or bidentate sheath, the upper ones longer and narrower, very shortly connate or free, with lance-acuminate, often divaricate, herbaceous blades, all thinly pubescent dorsally; leaves 1.5-6.5 cm. long, all slender-petioled or the uppermost shortly so to subsessile, with 9-15 narrowly to broadly elliptic, oblanceolate, rarely obovate-cuneate, acute or obtuse leaflets 3-14 (18) mm. long; peduncles solitary or rarely 2 (3) together in some upper axils, slender or subfiliform, 1.5-6.5 (8.5) cm. long, mostly shorter, rarely surpassing the leaf, incurved in fruit; racemes loosely or remotely 4—12-, exceptionally 15-20-flowered, the flowers early declined, the axis 1.5-4.5 (6) cm. long in fruit; bracts submembranous, ovate- or lance-acuminate, 1-2.5 mm. long; pedicels slender, at anthesis 0.7-1.5 (2) mm. long, in fruit either straight and spreading or arcuately recurved, 1.2-2.2 (2.5) mm. long; bracteoles 0; calyx 2.7-3.8 (4.3) mm. long, densely strigulose-pilosulous with white, or black and white hairs, the subsymmetric disc 0.4-0.7 mm. deep, the campanulate tube 1.5-2.2 mm. long, 1.6-2 mm. in diameter, the lance-subulate or subsetaceous teeth 1-2 (2.3) mm. long; petals pink or magenta-purple, more rarely whitish tipped with pink, the banner prominently purple-veined, the wing-tips often pallid or white; banner recurved through ± 90°, broadly ovate-cuneate, or the blade suborbicular, 5.1 7.8 (8.3) mm. long, 4-6.4 mm. wide; wings 4.6-6.5 (6.8) mm. long, the claws 1.4-2 mm., the obliquely obovate or half-obovate, obtuse or emarginate blades 3.5-5.1 (5.5) mm. long, 1.6-2.6 mm. wide, one wider than the other, the left one more strongly incurved than the right and its blade infolded; keel 3.7-4.8 mm. long, the claws 1.4-1.8 mm., the half-obovate blades 2.2-3.4 mm. long, 1.42.1 mm. wide, abruptly incurved through 95-110° to the bluntly deltoid, obscurely porrect apex; anthers 0.3-0.45 mm. long; pod spreading from horizontal or declined from ascending raceme-axes, sessile, plumply ellipsoid, obovoid-ellipsoid, or subglobose, bladdery-inflated but only 5-12 (14) mm. long and 4-6 (or when pressed apparently up to 7) mm. in diameter, somewhat oblique, the dorsal suture more strongly convex than the ventral, rounded or obconic at base, obtuse or with a minute conic beak at apex, often merely apiculate by the persistent, incurved style, neither compressed nor sulcate, the valves a trifle fleshy when first formed (and then tending to dry black), becoming papery-membranous, stramineous or brownish, delicately reticulate, shortly but usually densely pilosulous with white and sometimes a few black hairs, not inflexed, the funicular flange 0; dehiscence very tardy, after falling, apparently apical; ovules 6—8 (9); seeds olivaceous, brown, or black, smooth but dull, 2.3-3.2 mm. long.
Distribution and Ecology - Rocky and grassy hillsides, gravelly flats, usually in stiff soils and open places, sometimes on sandy lake or stony river shores, rarely in thin pine forest, 1250-6200 feet, locally common along the upper Columbia River and its affluents from near the mouth of the Spokane, northeastern Washington and adjoining British Columbia, eastward up the Pend Oreille and Clarks Fork to the Big Blackfoot and Deer Lodge Valleys, westcentral Montana, extending just across the Continental Divide into the upper Missouri Valley near Helena. — Map No. 36. — Late April to August.
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Discussion
The least bladdery milk-vetch, A. microcystis, and the related A. vexilliflexus are a troublesome pair of species. So closely do some flowering specimens of the one simulate the other in all technical characters up to the totally distinctive fruits that material collected at this stage has often been misidentified, with consequent widespread confusion as to the geographic distribution. Thus Jones (1923, p. 98, as A. miser) attributed to A. microcystis not only a synonym (A. amphidoxus) properly belonging to A. vexilliflexus, but a range of dispersal extending east and south to the east base of the Rocky Mountains and central Wyoming; at the same time many herbarium specimens of genuine A. microcystis from western Montana have found their way into the A. vexilliflexus folder. Actually I have have only one positive record of the latter species (Deer Lodge Valley, Jones in 1905, POM) from the Pacific slope in Montana, and A. microcystis has been traced eastward across the Divide only very locally into extreme southern Lewis and Clark and adjoining Jefferson Counties. The least bladdery milk-vetch seems here to be an immigrant from across the low water parting that separates the Deer Lodge and Missouri Valleys, for its areas of abundance are in the Columbia drainage. Thus in practice there should seldom be any doubt as to the identity even of young material provided its origin is known. A reputed hybrid ("A. miser X pauciflorus") mentioned by Jones (l.c.) as "about intermediate" between the two species has not been identified at POM where an annotated specimen might be expected; but the term hybrid was employed freely by Jones as a smoke-screen to cover ambiguous specimens, and I must look with skepticism on the existence of such a cross.
A modest, loosely tufted or trailing astragalus, A. microcystis is chiefly remarkable for its small, swollen fruits which vary somewhat in outline but are most often broadest a little above the middle and obliquely obovoid. The plants are usually less ornamental than A. vexilliflexus, owing to the pallor of the petals and higher ratio of leaf to flower. But occasional plants with relatively ample and purple flowers are pretty enough. The species is not greatly variable, except in superficial matters of stature and luxuriance; it is the plants from the lower elevations and from lake shores that tend to have longer stems, wider leaflets, more numerous flowers, and larger pods than those from stony situations in the mountains.
About the headwaters of Clarks Fork, A. microcystis is found in a variety of habitats and is both comparatively common and locally abundant. From Lake Pend Oreille westward, it is rarer and apparently confined to the shores of lakes and rivers. Probably the populations in Idaho and Washington are the progeny of water-borne introductions from the original home of the species in mountain valleys near the Continental Divide.
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Objects
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Distribution
British Columbia Canada North America| Washington United States of America North America| Idaho United States of America North America| Montana United States of America North America|