Astragalus Cusickii

  • Title

    Astragalus Cusickii

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus cusickii A.Gray

  • Description

    86. Astragalus Cusickii

    Slender but rather tall, sparsely leafy and often rushlike, with a thick woody taproot and at length shortly forking caudex, thinly strigulose with straight, appressed hairs up to 0.3-0.5 mm. long, the green, striate stems glabrous or nearly so, the leaflets green, either glabrous or strigulose above; stems several or numerous, erect and ascending in bushy clumps, rarely diffuse or pendulous from cliff- ledges, 3-7 dm. long, paniculately branched from near the base, or at least at several nodes preceding the first peduncle; stipules (0.5) 1-4.5 mm. long, the lowest early becoming papery, at least in vernation fully amplexicaul and connate into a subentire or bidentate sheath (commonly ruptured by expansion of the stem and then appearing as a low, imperfectly amplexicaul collar), the median and upper ones small, inconspicuous, united by a stipular line or only semiamplexicaul, with erect, triangular or subulate, herbaceous blades; leaves commonly divaricate and incurved, 4-10 (13) cm. long, with slender, tapering rachis and (5) 7-15 (17) distant, linear or linear-filiform, acute, subobtuse, involute, or (in some lower leaves) linear-oblanceolate and retuse, flat leaflets 2—22 mm. long, those of the upper leaves usually reduced in size, number, or both, and the terminal one either jointed like the lateral or confluent with the rachis; peduncles slender, erect or incurved-ascending, 5—15 (22) cm. long; racemes loosely (3) 4—14 (18)- flowered, the flowers early spreading and then declined, the axis 1—8.5 cm. long in fruit; bracts submembranous, ovate or subulate, 0.8—1.5 mm. long; pedicels at anthesis ascending, straight, (1.2) 1.5—2 mm. long, in fruit ascending or arched outward, 1.5—3.5 mm. long; bracteoles 0, rarely a minute scale; calyx 4—6.7 mm. long, minutely strigulose with black or mixed black and white hairs, the subsymmetric disc 0.7—1.5 mm. deep, the tube 3.2—5.8 mm. long, the deltoid or broadly triangular-subulate teeth 0.5—1 mm. long, the whole becoming papery, marcescent unruptured; petals white, creamy-white, or purplish; banner recurved through ± 40°, 12.5-15.5 mm. long, 5-7.5 mm. wide; wings 10.2-14 mm. long, the claws 3.5—6.2 mm., the obovate or oblanceolate, obtuse, slightly incurved blades 7—9.3 mm long, 2—3 mm. wide; keel 8—11 mm. long, the claws 4.1—6 mm., the half- obovate, -obcordate, or lunately elliptic blades 4.3—5.2 mm. long, 2.3—2.9 mm. wide, abruptly incurved through 95—100° to the bluntly deltoid or triangular, often slightly porrect apex; anthers 0.45—0.6 mm. long; pod loosely pendulous, stipitate, the filiform, purplish, sometimes puberulent stipe ± twice as long as the calyx, the body obliquely obovoid, half-obovoid or -ellipsoid, bladdery-inflated, (1.6) 2-4.8 cm. long, (5) 6-16 (when pressed, apparently up to 22) mm. in diameter, commonly broadest above the middle, contracted distally into an oblique, deltoid or deltoid-apiculate beak, the filiform, often purplish ventral suture varying from strongly convex to straight or a trifle concave in profile, the papery-membranous, subdiaphanous, delicately reticulate, glabrous valves at first pale green, sometimes faintly mottled, becoming stramineous or pearly-white and lustrous, not inflexed; ovules 10-20; seeds brown, sometimes purple-speckled or -mottled, smooth but scarcely lustrous, 2.9-3.5 (4) mm. long.

    The Cusick milk-vetch is virtually endemic to the great troughs formed by the passage of the Snake and lower Salmon Rivers through the mountains along the Oregon-Idaho boundary, but even in this quite restricted area of dispersal it has become racially modified. The canyons of the two main streams are so deeply entrenched that even where they flow in approximately parallel directions and approach each other within seven or eight miles, the intervening ridges form an effective barrier to such plants as A. Cusickii which are confined to the banks and terraces immediately above the valley floor. This physical isolation has played a decisive role in shaping the evolution of A. Cusickii var. flexilipes along the lower Salmon River. At the present time the mouth of the Salmon provides the one point of contact between var. Cusickii and var. flexilipes, and it is interesting to find that near the confluence of the two streams, and thence downstream to the mouth of the Grande Ronde, the ideal differential characters of the two varieties are variably and perplexingly combined, so that it becomes possible to assemble an uninterrupted series of individual variants ranging from almost perfect var. flexilipes with white flowers to a coarse, large-flowered var. Cusickii with strongly inflated but oblique legume. The following key is ineffective in this area.