Astragalus canadensis L.
-
Authors
Rupert C. Barneby
-
Authority
Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(2): 597-1188.
-
Family
Fabaceae
-
Scientific Name
-
Type
“Habitat in Virginia, Canada."—Holotypus, labeled “Astragalus 3, Hort. Cliffort.,” LINN!
-
Description
Species Description - Usually robust, more rarely quite slender caulescent perennials, the stems arising singly and few together from oblique or horizontally spreading, at length woody rhizomes, more or less densely strigulose with straight or largely straight, appressed and subappressed, dolabriform hairs up to 0.3-0.9 (1) mm. long, the leaflets commonly glabrous but sometimes densely pubescent above, the inflorescence (especially the bracts) nearly always pilosulous with some longer, looser, basifixed hairs up to 0.5-1.1 mm. long, the herbage green or sometimes cinereous, the thin-textured, often visibly nerved leaflets usually somewhat bicolored, paler beneath than above; stems mostly erect, sometimes decumbent and ascending, (1) 1.5-10 dm. long, fistular when stout, green or purplish, leaflets at base, simple or branching upward; stipules deltoid, deltoid-acuminate, or lanceolate, 3-18 mm. long, membranous, pallid, early becoming scarious, the lower ones often fragile and deciduous by late anthesis leaving a scar or low ridge around the stem, at least the lowest ones and those of the more slender spurs or branches (often all) amplexicaul and connate into a bidentate sheath, this sometimes ruptured by expansion of the stem, the median and upper ones commonly decurrent around about half the stem’s circumference, all thinly pubescent dorsally and often beset, especially at the point of insertion, with a few minute knob- or tack-shaped processes; leaves (3) 5-35 cm. long, shortly petioled or the upper ones subsessile, with (7) 13-35 broadly lanceolate, lance-oblong, ovate-oblong, or elliptic, rarely obcordate, obtuse and mucronulate, obtuse, or shallowly emarginate, flat leaflets (0.5) 1-4.5 (5) mm. long; peduncles erect or incurved-ascending, (2.5) 4-22 cm. long; racemes densely (in the Appalachian region sometimes rather openly) many-flowered, the mostly subcontiguous flowers ascending in bud, early spreading and then declined and nearly always retrorsely imbricated, forming an at first tapering or ovoid but at full anthesis cylindric spike 2.5-16 cm. long, 2.5-3.5 cm. in diameter, the axis little elongating, the erect fruits crowded into an oblong heads; bracts membranous, pallid, narrowly lance-acuminate or linear-caudate (exceptionally ovate), (1.2) 2-10 mm. long, reflexed in fruit; pedicels ascending or a little arched outward, at anthesis 0.5-1.7 mm., in fruit erect or ascending, straight, thickened, 1.2-3.5 (4) mm. long; bracteoles 0-2, commonly present; calyx (4.6) 5.5-10.5 (11) mm. long, strigulose or pilosulous with white, fuscous, or black hairs, sometimes subglabrous medially, the strongly oblique disc (0.7) 1-2 mm. deep, the campanulate or rarely cylindro-campanulate tube (3.4) 4.1-8.5 (9) mm. long, the subulate, linear-subulate, or triangular teeth (1) 1.2-4.4 mm. long, the whole becoming papery, ruptured, marcescent; petals greenish-white, cream-color, dull straw-yellow, or greenish tinged with dull or lurid purple; banner broadly oblanceolate or spatulate, shallowly notched, (11.3) 13.2-17 (17.5) mm. long, (4.3) 4.7-8.2 mm. wide; wings (10.1) 11.3-15.3 mm. long, the blades narrowly oblong or lance-oblong, obtuse, obliquely truncate, or rarely bidentate, straight or distally a trifle incurved, the inner margin crispate-undulate toward the middle, the auricle large, mostly 1.2-2.4 mm. long; keel (9.5) 10.2-13.6 mm. long, the blades obliquely oval, half-oval, or -obovate, gently or quite abruptly incurved through 90-95° to the blunt deltoid apex; anthers 0.5-0.75 (0.8) mm. long; pod erect, sessile on the slightly elevated receptacle, oblong-cylindroid or -ellipsoid, (9) 10-20 mm. long, 2.9-5.2 mm. in diameter, rounded or truncate at base, abruptly contracted distally into a rigid, erect or quite strongly porrect, cusplike beak 1.5-5 mm. long, either terete or grooved dorsally, obtusely carinate ventrally by the prominent, thick suture, the green, somewhat fleshy, glabrous, strigulose, or exceptionally villosulous valves becoming stiffly papery or leathery, brown and ultimately blackish, transversely rugulose-reticulate and sometimes also tuberculate and wrinkled lengthwise, filamentous within, inflexed as a complete or subcomplete septum 1.5—4.5 mm. wide; dehiscence tardy, through the beak and part way downward through the ventral suture; ovules (16) 18-26 (28); seeds greenish, ochraceous, grayish-brown, or castaneous, smooth but dull, 1.7-2.4 mm. long.
-
Discussion
The Canada milk-vetch is easily recognized in our flora by its combination of rhizomatous root-svstem (unfortunately shown by only a small proportion of the herbariums specimens), dolabriform vesture, at least some connate stipules, nodding flowers of dingy greenish- or yellowish-white sometimes tinged with lurid purple, and by the rather small, erect, fully bilocular pods of oblong-ellipsoid outline. It is the New World’s most widely dispersed astragalus, ranging from the Gulf Coast in eastern Texas to the Appalachians and lower St. Lawrence River, west to the southern Rocky Mountains and the Great and Columbia Basins, where it is found in a variety of habitats, its one consistent requirement being plentiful moisture at least during the period of active growth. The adaptation of A. canadensis to diverse climates, soils, and environments has gone hand in hand with racial differentiation, although this is not of a marked character. The species is readily divisible into two main branches, one widespread east of the Rocky Mountains and the other primarily intermontane, although each intrudes here and there across the Continental Divide, as noted below in greater detail. The eastern branch is characterized by a terete pod, the western one by a pod more or less deeply grooved dorsally. It has often been claimed that the eastern plants, including with the Linnean A. canadensis the var. longilobus, A. carolinianus, and A. Halei, are distinguished from their western counterparts by a glabrous pod but this is not always so. In the upper Mississippi Valley, especially in Minnesota, the ovary of typical A. canadensis is often puberulent, and the ripe pod is occasionally quite densely strigulose; occasionally in the Northwest a very thinly puberulent ovary ripening into an almost or truly glabrous, dorsally sulcate fruit is encountered. This character of pubescence, which would be so useful in the case of flowering material, cannot unfortunately be relied on, although it may be of limited use at the points where the two principal branches of the species coincide in range.
Both east and west of the Rocky Mountains racial differentiation is evidently in progress; the modifications, however, are very slight and the emergent races for the most part impossible to define in mutually exclusive terms. In the East, there are faint and indecisive signs of a northward and southward dichotomy, mentioned further under var. canadensis. The western material falls into two fairly well-marked categories in which small morphological differences are correlated with habitat and distribution. The species is understood here to be composed of three varieties.
For over two centuries it has been recognized that A. canadensis is related to the Siberian A. uliginosus L., which seems to be separable from some of the western forms of Canada milk-vetch with sulcate pods chiefly by its ordinarily glabrous (but perhaps sometimes puberulent-cf. Komarov, Pl. Manshur. 951, NY) ovary and broadly lance- or ovate-acuminate bracts. In the context of the section and genus these differential characters are trifling enough, and I have no doubt that despite the great discontinuity in range the eastern Asiatic and North American plants should be considered as forming parts of a bicentrically dispersed species. Lack of material of the related A. Schelichovii Turcz. and A. kamtschaticus (Kom.) Gontsch. has prevented a thorough study of the problem without which changes in nomenclatural status would be improper. Granted that A. canadensis is derived from Asia, as I have speculated elsewhere, it would most nearly reflect the biological realities if the New World forms were reduced to varietal status under A. uliginosus L.