Sometimes considered a difficult genus, but our species are rather easily recognized; the major problems arise from hybridization (or from efforts to name recognizable varieties in some of the highly variable species). Hybrids are fairly frequent in the genus, and combine parental characters in various ways, including intermediate sizes and shapes. Plants in the shade may have larger leaflets, longer petioles, and longer internodes than sun forms and hence appear quite different.
In addition to conspicuous petaliferous flowers, species of Lespedeza generally produce cleistogamous flowers in inconspicuous axillary clusters lower on the stem. The fruits from these flowers are easily recognized by the sharply recurved little style, which bends back on itself 180°.
1. Plants true shrubs, to 3 m tall; panicles or racemes of flowers aggregated into large, showy clusters at the ends of the branches.
2. Longest (lower) calyx lobes 1.2–2.4 mm long, equaling or shorter than tube.
2. Longest (lower) calyx lobes 2.5–3.3 (–4) mm long, clearly longer than tube.
1. Plants herbaceous, usually less than 1 m tall; flowers solitary or in small clusters, dense heads or somewhat open axillary clusters (except in L. frutescens).
3. Corolla yellow or cream (often drying orange-brown), often with a purplish spot at the base of the standard; calyx nearly equaling to exceeding the fruit.
4. Flowers solitary or 2–3 in the axils of numerous cauline leaves (which exceed them); leaflets mostly 2–4.5 mm wide, broadest near the apex.
4. Flowers crowded into dense head-like clusters at and near the end of the stem, these often exceeding the subtending leaves; leaflets (at least the terminal ones) mostly 5 mm or more wide, broadest near or slightly above the middle.
5. Leaflets over 2 (usually ca. 3) times as long as wide, narrowly elliptic-oblong; peduncles usually shorter than inflorescences and shorter than subtending leaves; calyx lobes (4–) 5–8 (–10) mm long.
5. Leaflets less than twice as long as wide, elliptic-oblong to obovate; peduncles usually ± equaling or longer than the inflorescences and longer than subtending leaves; calyx lobes (3.5–) 4–6.5 mm long.
3. Corolla purple; calyx at most about half as long as the fruit.
6. Stems trailing, downy with spreading pubescence.
6. Stems erect (or ascending), glabrous or with appressed hairs (if pubescence spreading, suspect a hybrid).
7. Petaliferous flowers in inflorescences most or all of which are on very slender peduncles exceeding the leaves (cleistogamous flowers in axillary clusters); calyx teeth of cleistogamous fruit less than a 1/4 as long as the fruit; keel of corolla longer than the wings; leaflets less than twice as long as broad.
7. Petaliferous flowers in inflorescences on peduncles not exceeding the leaves; calyx teeth of cleistogamous fruit usually about a fourth as long as the fruit or slightly longer; keel of corolla shorter than the wings; leaflets ca. 2–6 times as long as broad.
8. Leaflets glabrous (or rarely with a few hairs near midvein) above, at least the longer ones 2–3 times as long as wide, oblong-elliptic.
8. Leaflets finely strigose above, at least the longer ones (3–) 4–6 (–8) times as long as wide, quite narrowly oblong- or linear-elliptic.