Plants herbaceous perennials or shrubs, often with multiple stems from a woody caudex. Stems erect to spreading, unbranched or branched, unarmed, sparsely to densely pubescent with appressed to spreading, unbranched hairs. Leaves pinnately trifoliate, short- to long-petiolate. Stipules hairlike to linear-triangular or less commonly lanceolate, herbaceous or more commonly papery, attached at the base, the margins entire, pubescent on the outer face, with 1 or rarely few prominent, unbranched vein(s), persistent; stipels lacking. Leaflets narrowly oblong to broadly ovate, the lateral leaflets often slightly shorter than the terminal one, rounded or angled to a stalked base, mostly rounded at the tip, sometimes shallowly notched or with an abrupt, minute, sharp point at the very tip, the margins entire, the surfaces glabrous or more commonly hairy, with a prominent midvein and conspicuous pinnate secondary veins. Inflorescences ascending to spreading, racemes or spikes (sometimes appearing grouped into panicles), or reduced to few-flowered clusters, well separated to tightly clustered and obscuring the inflorescence axis, the 3 bracts subtending each pair of flowers and 2 bractlets subtending each flower all minute, linear, inconspicuous. Cleistogamous flowers often present, usually mixed with open flowers in the same inflorescence. Calyces 5-lobed, the lobes as long as or longer than the tube, nearly equal in length, but the upper 2 lobes fused nearly to the tip, minutely hairy, persistent but not enlarging at fruiting. Corollas papilionaceous (highly reduced in cleistogamous flowers), glabrous, pinkish purple, yellowish, or cream-colored, often with purple near the base of the banner petal, the petals tapered to a short, stalklike base, the banner broadly obovate to oblong-obovate, abruptly curved-ascending above the midpoint, the wings oblong, about as long as and sometimes slightly fused to the keel toward the tip, the keel oblanceolate and curved in outline, boat-shaped. Stamens 10, 9 of the filaments fused and 1 free nearly to the base, the anthers small, attached near the midpoint, all similar in size. Ovary ellipsoid to ovoid, sessile or short-stalked, the style slender, usually glabrous, straight in chasmogamous flowers and recurved in cleistogamous flowers, persistent at fruiting, the stigma small and terminal. Fruits modified legumes, flattened, sessile or very short-stalked, those ripening from open flowers mostly elliptic and slightly longer, those from cleistogamous flowers broadly obovate to nearly circular and slightly shorter, often with a raised network of nerves, indehiscent, 1-seeded. Seeds slightly kidney-shaped to nearly circular in outline, sometimes with a shallow notch at the attachment point, somewhat flattened, the surface smooth, yellow or tan to nearly black, sometimes mottled. About 40 species, North America, Asia.

Lespedeza presents considerable challenges because the species display significant morphological variation. A number of additional species and infraspecific taxa have been proposed to accommodate this variation, but in most cases these do not seem discrete enough morphologically to warrant formal recognition. Much of the complexity apparently arises due to hybridization (Clewell, 1964, 1966a, c). The eight native species in Missouri could produce 27 possible biparental hybrids, and Clewell (1966b) has hypothesized each of these crosses based on progeny arrays reared in a garden from putative hybrid plants, field observations of co-occurring species, and examination of herbarium specimens. Offspring from crosses involving morphologically disparate species, for example from yellow-flowered taxa crossed with purple-flowered ones, can be conspicuous. However, hybridization between similar species may go undetected and could account for the seeming morphological continuum among similar species, for example the problems in distinguishing L. virginica, L. stuevei, and L. violacea.

Species frequently occur in mixed populations, but the number of individuals showing hybrid morphology is generally extremely low (less than 1%). Whenever aberrant plants are encountered, collectors are encouraged to record associated Lespedeza species, as field observations are among the greatest aids in determining the possible parental species of hybrids. The use of hypothesized hybrid parental formulas is encouraged in place of the many binomials that predate the appreciation of hybridization as a causal agent of morphological diversity (they originally were named as species rather than hybrids). The hybrid binomials, many of which were based on Missouri specimens (Mackenzie and Bush, 1902) may still be used, but because different crosses can result in similar hybrid morphology, some hybrid names may include multiple parental combinations.

Because of the morphological complexity of this genus, two keys are provided. One uses primarily vegetative features and the other uses largely reproductive traits. The dual keys provide different groupings, so important distinguishing morphology can be emphasized. Character states and measurements represent the morphological variation encountered within Missouri, and the following keys do not account for all of the variation found elsewhere in the ranges of the species.