Astragalus coltonii M.E.Jones
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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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Description
Species Description - Variably but usually sparsely leafy, sometimes apparently leafless and jun- ceous, strigulose with straight, appressed, filiform or somewhat flattened hairs, the herbage green or cinereous; stems arising from a subterranean root-crown (as typical of the section) or rarely (in var. Coltoni) from divisions of an aerial, eventually suffruticulose caudex, usually several or numerous, erect and ascending in clumps, 1-4 dm. long, naked and purplish at base, branched or spurred at base or at 1-3 nodes preceding the first peduncle, the branches sometimes disposed in unequal pairs (threes) to an axil, or (upward) inserted between a peduncle and its subtending leaf; stipules 1-7 mm. long, dimorphic, the lowest papery, pallid or brownish, approximate or sometimes imbricated, strongly adnate to a vestigial petiole to form a subtruncate or bidentate sheath, decurrent around ½ to the whole stem’s circumference but free, the upper ones smaller, herbaceous, obscurely adnate, with deltoid or triangular-acuminate, often spreading or deflexed blades; leaves 2-10 cm. long, variable according to the var., either all imparipinnate, or all (or nearly all) reduced to the naked rachis; peduncles erect or strictly incurved-ascending, (4) 6.5-30 cm. long, the lowest 1-2 usually much longer and stouter than the rest and far surpassing the leaves, the racemes mostly projected well beyond the leafy part of the plant; racemes loosely (2) 5-30-flowered, the axis elongating, (1.5) 3-16 cm. long in fruit; bracts membranous, ovate or lanceolate, 0.5-3.2 mm. long; pedicels at first ascending, 0.8-1.5 mm. long, early arched outward or decurved, sometimes horizontally spreading, in fruit thickened, 1-2.5 mm. long; bracteoles 0, rarely a minute scale; calyx 4.5-8 mm. long, densely to quite thinly black-strigulose, the oblique disc 0.9-1.5 (1.8) mm. deep, the membranous, purplish, deeply campanulate or cylindric tube 4-6.7 mm. long, 2.3—3.7 mm. in diameter, the deltoid, triangular, or broadly subulate, often obtuse teeth 0.6-1.8 (2.3) mm. long, the ventral pair commonly shortest, the orifice strongly or little oblique; petals bright pink-purple, drying bluish, the wing-tips often paler; banner broadly rhombic-elliptic, -obovate, or broadly spatulate, notched or scarcely emarginate, 12-18.5 mm. long, (6) 6.5-12.5 mm. wide; wings as long or a little shorter, 11-18.3 mm. long, the claws 5.3-7.8 mm., the narrowly lanceolate, oblong-elliptic, or -oblanceolate, obtuse, subtruncate, or obliquely emarginate, straight or slightly incurved blades 8.6-11.8 mm. long, 2.3 3.5 mm. wide; keel 9-13 mm. long, the claws 4.9—7.4 mm., the half-obovate or lunately half-elliptic blades 4.6—6.6 mm. long, 2.3—3.5 mm. wide, incurved through 85—95° to the triangular-deltoid, sometimes slightly porrect and subacute apex; anthers (0.55) 0.6-0.9 (1) mm. long; pod pendulous, stipitate, the slender stipe 4-11 mm. long, the body oblong, linear-oblong, or -oblanceolate, 1.9-3.5 cm. long, (3) 3.5-6 mm. in diameter, straight or gently decurved, narrowly cuneate at base or tapering gradually downward into the stipe, cuneate-cuspidate at apex, strongly compressed laterally and 2-sided, bicarinate by the subfiliform but salient sutures, the faces low-convex, the somewhat fleshy, green or reddish, glabrous valves becoming stiffly papery, stramineous, almost smooth to faintly rugulose and cross-reticulate; ovules 14-20; seeds brown or olivaceous, sometimes purple- speckled, sparsely punctate, sublustrous, (2.9) 3.2-4.4 mm. long.
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Discussion
In the past the Colton milk-vetch has been aligned with A. filipes, which has a similarly compressed and stipitate pod, in Homalobus or the equivalent sect. Homalobi. Both Rydberg (1929, p. 272) and Jones (1923, p. 70) have described the stipules of A. Coltoni as connate, but this is not strictly correct. The lowest ones do form a bidentate, more or less amplexicaul sheath; however they are united not, as in A. filipes, by their contrapetiolar margins, but only by adherence to a vestigial petiole and thus have the structure and appearance characteristic of all genuine Lonchocarpi. Even though the pods of A. Coltoni and A. filipes are so much alike in outward form, their mode of dehiscence is somewhat different. In the Lonchocarpi dehiscence starts in the beak and proceeds downward through the ventral or both sutures, whereas the ripe pod of A. filipes and its close kindred splits open simultaneously through the beak and stipe. The close relationship of A. Coltoni to other Lonchocarpi only became truly apparent with the discovery of A. Ripleyi, a species easily mistaken for A. lonchocarpus except for its laterally compressed pod.
The species is extremely variable, especially in the development of the foliage, and consequently in gross aspect. The differences in flower-size, width of the pod, and position of the root-crown, once thought (Barneby, 1944, p. 49) sufficient to separate A. canovirens (= var. moabensis) from genuine A. Coltoni at the specific level, have failed to pass the test's of observation in the field and study of more material. The calyx and petals are now known to vary within nearly the same limits in both supposed species, the known extremes in both directions having been secured from populations of var. Coltoni in the type-region along the Price River. The average pod of var. moabensis is perhaps a little broader, but it varies considerably in length and girth. The position of the caudex depends, in the case of A. Coltoni, on environment of the individual plant. On rocky slopes or rock ledges the caudex is exposed, apparently more by weathering than by nature, and may become decidedly woody with lapse of time. But on hills of soft clay or on cobblestone bluffs, otherwise similar plants have the buried root- crown or caudex characteristic of var. moabensis and other members of the section. Typical var. moabensis is distinguished, unless depauperate, by having the proper stem longer in proportion to the more robust lower peduncles, and usually also by its more numerous and better-developed leaflets. However in San Juan and Grand Counties, Utah, and especially at low elevations in the trough of the Grand River, the terminal leaflet may vary from one plant to the next in a small group, now distinctly petiolulate and now clearly decurrent, but often separated from the rachis by a strangulation or a barely perceptible change in texture. Collections from the neighborhood of Cane Springs (e.g., Barneby 12,757), close to the probable type-locality of A. canovirens, are intermediate in all the critical characters, some individuals leaning toward var. Coltoni as ideally conceived, others closely approaching typical var. moabensis.
The pod of A. Coltoni is ordinarily unilocular as in most Lonchocarpi, but close examination occasionally reveals an incipient septum up to 0.5 mm. wide. The species is perhaps a loco-weed, for var. moabensis is reported toxic to swine.