Astragalus convallarius Greene
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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
"Sandy plains of the Colorado of the West, near the sources of the Platte. Nuttall."—Holotypus, labeled by Nuttall "Homalobus *campestris. Colorado of the Wt./R. Mts.," BM! isotypi, GH, K, PH!
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Description
Species Description - Commonly slender, wiry, sparsely leafy or apparently almost leafless and rushlike, with a taproot and subterranean root-crown, densely to quite thinly strigulose with straight, appressed or narrowly ascending, filiform or somewhat flattened hairs up to 0.3-0.6 (0.7) mm. long, the stems and herbage greenish-cinereous, cinereous, or sometimes canescent, the leaflets (when present) either equally pubescent on both sides or glabrescent to quite glabrous above; stems usually few, commonly ± 4-6, sometimes solitary, rarely up to 37, erect, ascending, or exceptionally diffuse or prostrate, (1) 1.5-8 dm. long, subterranean for a space of 1-7 cm., simple, leafless, commonly purplish at base, thereafter (sometimes at the first emersed node, usually beyond it) bearing divaricate-ascending or rather strict branches or spurs at 1-6 nodes preceding the first peduncle, the branches sometimes again branched, those of the primary axis often paired with a smaller branch, a spur, or a peduncle, or the peduncles paired distally, the whole becoming flexuous or zigzag distally, striate throughout; stipules ± dimorphic, those at the buried and lower emersed nodes papery-scarious, pallid or purplish-brown, often several- nerved, (1) 2-7 mm. long, amplexicaul and connate into a campanulate sheath, the median and upper ones nearly always smaller, herbaceous, ovate, triangular, or deltoid, commonly only semiamplexicaul, rarely briefly united at base; leaves 2-11 cm. long, the leaflets of the upper leaves, sometimes of all, greatly reduced, wanting, or decurrent on the rachis, when present up to 6 pairs, then distant, linear, linear-oblong, or -oblanceolate, involute or rarely flat, up to 25 (33) mm. long, mostly much shorter; peduncles erect, incurved-ascending, or divaricate, (1) 3-14 cm. long, either longer or shorter than the leaf; racemes very loosely or remotely (1) 3-25-flowered, the flowers early spreading, at length declined and often irregularly secund, the axis (0.5) 2-18 (23) cm. long in fruit; bracts thinly herbaceous becoming papery, ovate or lanceolate, 0.5-2.3 mm. long, greenish, pallid, or purple-tinged; pedicels slender or subfiliform, at anthesis ascending at a wide angle or arched outward, 1—4.5 mm. long, in fruit straight and ascending, straight and divaricate, geniculate at base and refracted, or tortuous, 2—8 mm. long, tardily disjointing with the fruit; bracteoles 0—2, minute when present; calyx 4-6.3 mm. long, strigulose with black, white, or mixed hairs, the symmetric or slightly oblique disc 0.6-1 (1.4) mm. deep, the campanulate tube 3.4-5.4 mm. long, rounded or obliquely turbinate at base, sometimes a trifle constricted at the mouth and then obscurely urceolate, the broadly subulate, triangular, or deltoid, mostly obtuse teeth 0.5-1.4 mm. long, the whole becoming papery, marcescent unruptured; petals ochroleucous, ochroleucous veined or tinged with dull purple, sometimes bright rose-purple, all strongly incurved through at least a right angle, usually not strongly graduated, the wings (detached) often a trifle longer than the banner but arched in a longer and wider arc and so, in situ, appearing shorter; banner (6.6) 7-11.2 mm. long, the shortly cuneate claw abruptly expanded into a broadly ovate, rhombic- ovate, suborbicular, or inversely reniform, shallowly and openly notched or entire blade 5—8.2 mm. wide; wings (7) 7.7—12.6 mm. long, the claws (3) 3.5—5.6 mm., the lunately oblong, oblong-oblanceolate, or obliquely obovate, obtuse, often erose, or sometimes subemarginate blades 3.5-7 mm. long, (1.6) 2—3 mm. wide, their inner margins commonly infolded and once or more undulately notched near the middle; keel (6.2) 6.5-9.4 mm. long, the claws (3) 3.2-5.4 mm., the lunately triangular, or lunately half-circular blades 3.5-6.1 mm. long, 2.2-3.6 mm. wide, abruptly incurved through 100-125° to the triangular or sometimes triangular- acuminate, subacute or obtuse, often obscurely porrect apex; anthers 0.55—0.75 mm. long; pod essentially pendulous, but spreading vertically from divaricate peduncles and then (in pressed material) apparently horizontal, sessile but sometimes basally attenuate and then appearing very shortly and obscurely stipitate, the body linear, linear-oblong, linear-acuminate, or sometimes attenuate downward from near the apex and then oblanceolate in profile, straight or a trifle arched either way, 1.3-5 cm. long, 2.3-4 mm. in diameter, laterally compressed, bicarinate by the slender sutures, the faces flat when young becoming distended and low-convex at maturity, the thin, pale green, purplish, or purple-mottled, strigulose valves becoming papery, stramineous, delicately cross-reticulate, not inflexed; dehiscence apical and downward through both sutures, the valves ultimately separating to the base and coiling outward; ovules (11) 13—26; seeds brown or olivaceous, sometimes purple-speckled, smooth and lustrous, or ± pitted or rugulose and then either dull or shining, 1.8-4.3 mm. long.
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Discussion
The lesser rushy milk-vetch, A. convallarius, is a variable species but usually recognized at a glance by its sparsely leafy or apparently leafless stems arising from a buried root-crown and genuinely leafless at base, and especially by its small, loosely racemose flowers with petals little graduated and all very strong incurved. Apart from its mesophytic counterpart, A. diversifolius, of which the differential characters have been mentioned in the sectional key, only a few Lonchocarpi, especially the members of subsect. Pseudogenistoidei, resemble A. convallarius in all these features. They differ in having all the stipules free, the lowest ones moreover larger (not smaller) than the succeeding ones and several- or many-nerved. The Pseudogenistoidei are rare species, endemic to Arizona, outside the known range of A. convallarius.