This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs, sometimes woody, mostly with odd-pinnate leaves of several or many leaflets, and purple violet white or yellow flowers in spikes or racemes, or rarely umbellate or solitary. Stipules present. Calyx tubular, its teeth nearly equal. Petals clawed; standard erect, ovate or oblong; wings oblong; keel obtuse, about equalling the wings. Stamens diadelphous; anthers all alike. Ovary sessile or stipitate; ovules 00. Pod sessile or stalked, dehiscent, 1-2-celled, very different in different species and affording the best characters in classification, accepted as generic by some authors. [Greek name of some leguminous plant.]
At least 1000 species, of wide geographic distribution, most abundant in northern Asia. In addition to the following, at least 175 others occur in the western and southern United States. Type species: Astragalus Onobrychis L.
* Pod 2-celled.
Plant densely villous-pubescent all over.
Plants glabrous, or grayish-pubescent.
Flowers yellowish; pod terete, glabrous.
Flowers purple; pod with a deep furrow, pubescent.
Pod finely appressed-pubescent.
Pod densely villous with white hairs.
** Pod 1-celled, but one or both sutures sometimes intruded.
Pod 2-grooved on the upper side (genus Diholcus Rydb.).
Pod not 2-grooved.
Pod slightly fleshy; leaflets persistent (genus Ctenophyllum Rydb.).
Pod papery or leathery; leaflets deciduous.
Pod cordate or triangular in section, the dorsal suture intruded (only slightly intruded in A.
Pod straight or nearly so (genus Tium Medic).
Flowers white or yellowish-white.
Pod triangular in cross-section; plant appressed-pubescent; western.
Pod cordate in cross-section; plant villous-pubescent; western
Pod somewhat compressed, the dorsal suture scarcely intruded,
Pod densely blackish or brownish-pubescent; stems diffuse.
Pod finely pubescent; stem erect.
Pod crescent-shaped (genus Holcophacos Rydb.).
Pod neither cordate nor triangular in cross-section, the dorsal suture not intruded.
Plants scapose, or very short-stemmed (genus Xylophacos Rydb.).
Plant villous; flowers yellow.
Pod straight or nearly so, nearly circular in cross-section.
Pod curved, 8-shaped in cross-section.
Pod flattened, with a partial partition (genus Atelophragma Rydb.).
Pod sessile, black-pubescent.
Pod stipitate, glabrous.
Pod not flattened, completely 1 -celled.
Pods small, transversely wrinkled, coriaceous (genus Microphacos Rydb.).
Pods large, smooth, papery.