Monographs Details: Astragalus
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
Scientific Name:Astragalus


Caulescent therophytes, caulescent and acaulescent chamaephytes and hemicryptophytes, and suffruticose or low fruticose (often spiny) phanerophytes (in North America seldom more than suffruticulose at base), with a taproot and (after the first season) an aerial, cespitose, or subterranean caudex (sometimes stoloniform and adventitiously rooting), ± pubescent (the inflorescence especially) with unicellular, basifixed or dolabriform hairs, exceptionally almost glabrous; stipules either cauline, or cauline and adnate to the petiole, or amplexicaul and connate into a contrapetiolar sheath; leaves alternate, commonly imparipinnate, the terminal leaflet sometimes wanting or reduced to a spine or a filiform appendage (but never a tendril), the lateral (or all) leaflets either petiolulate, or sessile, or more rarely decurrent into the ventrally grooved rachis, the leaflets in rare cases palmately 3-5- foliolate, or 1 and terminal, or (in some or all leaves) lacking and the leaf then reduced to the filiform rachis or a dilated phyllode, the rachis in ours seldom indurated and never (as often in the Old World) truly spiny; inflorescence axillary, sometimes appearing radical, pedunculate or sessile, the papilionaceous flowers racemose, subumbellate, or spicate, variously oriented at anthesis; bracts 1-2 (1 in North American species); bracteoles 0-2, attached at base of the calyx or on the pedicel; calyx campanulate or cylindric, obscurely 2-lipped, 5-toothed, ± thickened at base into a feebly nectariferous disc, either ruptured by the expanding fruit or marcescent unruptured about its base, sometimes (with us rarely) inflated in age and enveloping the fruit, rarely circumscissile above the disc; petals inserted on the disc, the banner always free, the claws of wings and keel either free (with us always so) or adnate to the staminal tube, all either deciduous or marcescent, glabrous or dorsally pubescent; banner recurved through 20-180° from the vertical, variable in outline, mostly emarginate at apex; wings commonly shorter than the banner and longer than the keel, clawed, the blade auriculate at base, the inner face bearing a pit shortly above the auricle; keel commonly shortest, the claws free from each other, the blades ± united by their exterior margins, obtuse (or exceptionally acute or even acutely appendaged), each bearing externally above the short basal auricle a protuberance fitting into (but not physically adherent to) the corresponding pit on the wing; stamens diadelphous (one monadelphous sp. in Asia), the vexillar one free, the filaments of the rest united for ± 3/4 their length; anthers eglandular, in 2 sets of 5, those of one set slightly larger; style glabrous, rarely pubescent distally; stigma minute, subsymmetrically terminal, glabrous or puberulent; ovary sessile or stipitate; pod exceedingly variable in orientation, size, shape, texture, and mode of compression, either sessile on and disjointing from the receptacle or from a stipelike gynophore, or sessile and persistent, or contracted at base into a stipe and then always persistent (but often deciduous with the disjointing pedicel and marcescent calyx), the body varying from linear to globose (or even broader than long) in dorsiventral view, nearly always asymmetric in profile, straight, or incurved, or more rarely decurved or coiled inward, varying in length from ± 2 mm. to ± 6 cm., and in compression from terete to laterally or dorsiventrally compressed, or trigonus (rarely tetragonous), often grooved along the dorsal (abaxial) side and carinate by the ± prominent ventral (adaxial) suture, the valves varying from thinly membranous (subdiaphanous) to thickly fleshy or pulpy turning woody on ripening, commonly reticulate externally (rarely smooth, or marginally winged, or transversely wrinkled, or otherwise roughened or appendaged), the cavity either filled with seeds (and also with pulpy filaments) or larger than the seeds (the pod then either tumescent or inflated, often bladdery), unilocular or sembilocular to fully bilocular by means of a recessive fold or thin double membrane (septum) formed by intrusion of the endocarp from the abaxial toward the adaxial suture; ovules 2-seriate, 2-many, borne on slender funicles sometimes united at base by a membrane or funicular flange simulating the septum (but issuing from the ventral suture), seeds compressed, either circular, or oblong, or mitten-shaped, or prismatic in lateral view, notched at the hilum.—A vast genus, rivaled for size only by Care)c, Solanum, and Senecio, its numbers variously estimated at 1200, 1600, and 2000 spp. (the total depending largely on the censor’s taxonomic viewpoint), most highly developed in arid continental, desert, and Mediterranean climates, circumboreal (except Greenland, where 1 sp. is sparingly introduced) in dispersal, most numerous in central Asia, Iran and Turkey, in western North America, and in the Andes of South America, extending south in the Old World to equatorial Africa and subtropical India, in North America to Honduras, and in South America to Patagonia, about 370 North American, 100 South American, the remainder gerontogean.

Astragalus L., Sp. Pl. 755. 1753 & Gen. Pl., Ed. 5, 335. 1754.—Generitypus (cf. sub. sect. Astragalo, p. 100), A. alpinus L.