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, often somewhat woody, with pinnately 3-foliolate leaves, small stipules, and small purple or whitish flowers in axillary clusters, heads or panicles. Flowers often of 2 kinds intermixed, the one petaliferous and mainly sterile, the other minute, apetalous, abundantly fertile. Calyx-lobes nearly equal, those of petaliferous flowers often longer than those of apetalous ones. Standard in the petaliferous flowers obovate or oblong, clawed; wings oblong; keel incurved. Stamens more or less diadelphous (9 and 1); anthers all alike.
Ovary sessile or stipitate, I-ovuled. Pods ovate, oblong, oval or suborbicular, flat, indehiscent, reticulated, composed of a single joint, or with a second stalk-like joint at the base, those of petaliferous flowers often sharper-pointed than those of apetalous ones. [Named for Lespedez, governor of Florida, patron of Michaux.]
Perennial native species; stipules subulate; calyx-lobes narrow.
Stems prostrate or trailing.
Glabrous or somewhat appressed-pubescent.
Downy-pubescent or tomentose.
Stems erect or ascending.
Peduncles manifest, mostly longer than the leaves.
Bushy-branched; petaliferous flowers paniculate.
Stems simple or little-branched; flowers racemose or subspicate.
Calyx of petaliferous flowers two-thirds as long as the pod or more,
Calyx of petaliferous flowers one-half as long as the pod or less.
Stem tomentose; leaves tomentose beneath.
Stem and leaves glabrate or appressed-pubescent.
Leaflets oval to suborbicular.
Peduncles shorter than the leaves, or flower-clusters sessile.
Calyx of petaliferous flowers less than one-half as long as the pod
Leaflets densely tomentose beneath.
Leaflets appressed-pubescent beneath or glabrate.
Leaflets oval to oblong.
Leaflets linear to linear-oblong.
Calyx of petaliferous flowers two-thirds as long as the pod or more
Flowers all complete; corolla whitish or yellowish; pod included or scarcely exserted.
Leaves oblong, ovate-oblong, or nearly orbicular.
Peduncles mostly exceeding the leaves.
Peduncles shorter than the leaves.
Leaves linear or linear-oblong; peduncles manifest, usually elongated.
Spikes interrupted, loosely-flowered.
Annual; stipules ovate; calyx-lobes broad; introduced species.