Astragalus Kentrophyta

  • Title

    Astragalus Kentrophyta

  • Authors

    Rupert C. Barneby

  • Scientific Name

    Astragalus kentrophyta A.Gray

  • Description

    94. Astragalus Kentrophyta

    Variable in growth-habit, commonly prostrate or diffuse, with repeatedly forking stems forming densely or sometimes quite loosely woven mats, or erinaceous cushions, 0.5-4 (5) dm. in diameter, or (in some lowland forms) suffruticulose at base, thence bushy-branched or with rigid, erect or assurgent herbaceous stems up to 4.5 dm. long, the whole strigulose, villosulous (villous), or hirsutulous with either basifixed or dolabriform hairs, the herbage commonly cinereous, sometimes greenish or silvery-canescent, often becoming stiff and prickly as the season advances, the leaflets either glabrous or pubescent above; stipules either all scarious from the first, or some herbaceous becoming papery or stiff and thorny, all (or at least the lowest of the year’s growth-cycle) connate into a bidentate sheath, the upper ones sometimes (rarely all) connate at base only, with erect or divaricate, lance-acuminate, spinulose-tipped or callous-mucronate blades; leaves (2) 4-26 mm. long, shortly petioled, with 3-9 pinnately or palmately disposed, linear-elliptic or -oblanceolate leaflets 1-17 mm. long, all continuous with the rachis, grooved ventrally or conduplicate-inrolled, keeled dorsally by the prominent midrib, this running out at apex into a glabrous, pallid or yellowish mucro or spinule (0.2) 0.5-2.5 mm. long; peduncles subobsolete or up to 1.5 (3) cm. long, often surpassed by the stipules or concealed in the stipular sheath, the 1-3, loosely racemose, ultimately declined flowers appearing axillary, the raceme-axis little elongating, 0-4 (7) mm. long in fruit, nearly always produced beyond the terminal flower; bracts membranous or scarious, ovate-acuminate, lanceolate, or linear-caudate and subsetaceous, 0.8-3.5 mm. long; pedicels slender or subfiliform, at anthesis ascending or arched outward, 0.5-1.7 mm. long, in fruit little elongating, arched outward or contorted, not thickened, 0.5-2 mm. long, finally disjointing; calyx (2) 2.4-6.5 (8.3) mm. long, strigulose or hirsutulous like the herbage with white, black, or mixed black and white hairs, the subsymmetric disc 0.4-0.8 mm. deep, the obconic-campanulate or hemispherical tube 1.3-2.8 (3.3) mm. long, 1.3-2.7 mm. in diameter, the subulate and subherbaceous, or linear-acuminate and firmly setaceous, often rigid and subspinescent teeth 0.8—3.8 (5) mm. long; petals whitish with pink- or purple-tipped keel, or pinkish-lilac throughout, or bicolored, with banner and keel pale to bright pink or purple (drying violet) and white or pallid wing-tips; banner recurved through ±45° sometimes further in withering, broadly obovate-cuneate, flabellate, elliptic-obovate, or oblanceolate, rather deeply notched, 4—10 mm. long; wings a little shorter or longer, the blades elliptic or oblanceolate, obtuse or subemarginate, both gently incurved but one of them usually more strongly so than the other and inner margin infolded toward or over the keel; keel much shorter, the blades half-obovate or -circular, abruptly incurved through (90) 95—110° to the bluntly deltoid, sometimes obscurely porrect apex; anthers 0.25-0.45 mm. long; pod declined or spreading, sessile, in profile either subsymmetrically ovate, elliptic, or oblong-elliptic and straight, or lance-acuminate and gently incurved, 3—10 mm. long, (1.4) 1.6—4 mm. in diameter, laterally compressed, bicarinate by the filiform sutures, the faces at first nearly flat becoming distended and convex as the seeds ripen, the thin, green valves becoming papery and stramineous, strigulose; seeds brown or ochraceous, sometimes purple-speckled, or greenish-purple throughout, commonly smooth but not highly lustrous, rarely pitted, 1.7-2.2 mm. long.

    The kentrophytas are distinguished from all other astragali by the few (3-9) leaflets at once continuous with the leaf-stalk and mucronate or spinulose at apex, and by their racemes, ordinarily subsessile in the leaf-axils, of one to three tiny flowers. The nearly always thick- textured leaflets are further strengthened by a corneous midrib prominent on the lower face; they tend to become rigid and prickly as the season advances, finally withering-persistent on the caudex branches. Easily recognized as forming part of the species in the wide sense, the varieties are most reliably distinguished from one another by the hair-attachment, the shape of the banner, and the number of ovules, characters which require somewhat minute observation, although in some specimens the growth-habit or the size and shape of the pod provide a short road to identification. The species has differentiated out into two branches: one composed of var. implexus and its local derivative var. danaus, mostly montane in distribution and doubtless primitive, with basifixed vesture, obcordate banner, and relatively numerous ovules; the other, largely of low or middle elevations and characterized by dolabriform vesture, oblanceolate banner, and few ovules, which has broken up into seven more or less easily defined geographic races. To one familiar with only a few aspects of A. Kentrophyta, it must seem a simple matter to recognize two coordinate species corresponding with these two groups of forms, but in reality there are many connecting links and the differential characters mentioned are not perfectly correlated. Thus var. Kentrophyta itself combines with the narrow banner, few ovules, and spinescent foliage of the lowland group a hair-attachment only obscurely dolabriform. The pronounced spinescent character of the malpighian-haired group is found at alpine elevations in var. danaus, an erinaceous cushion-plant with the pubescence and flowers of var. implexus. Furthermore, on the plateaus of central Utah, there is a series of perplexing forms which combine on the same plant the basifixed hairs and broad banner of var. implexus (to which they are referred below) with rigid foliage and few ovules, sometimes only three or four in some flowers. The var. coloradoensis, a pronounced xerophyte apparently derived from var. elatus, has dolabriform hairs together with a pluriovulate pod.

    The present account follows in most details a recent revision (Barneby, 1951), in which, due to misunderstanding of the requirements for valid publication of new names, the varieties were subordinated to A. tegetarius (= A. Kentrophyta var. implexus) rather than to the older A. Kentrophyta. The varietal key has been altered a little to cover variations observed subsequently, and expanded to include var. coloradoensis, now better understood, and the new var. Douglasii.