Plants perennial herbs (annuals or shrubs elsewhere). Stems spreading to more commonly ascending or erect, branched. Leaf blades unlobed, ovate to linear, narrowed to truncate or shallowly cordate at the base, rounded or pointed at the tip, all less than 3 cm wide, the margins toothed and sometimes with a narrow band of purplish red color. Stipules persistent, linear. Flowers solitary in the leaf axils or in small terminal and axillary clusters, the bractlets subtending the calyx absent. Calyces cup-shaped when the fruits are mature (enclosing the developing fruits), strongly 5-angled between the sepals, the sepals also somewhat keeled, fused about half way or more, the lobes triangular, the margins (and sometimes also the keels) sometimes with a narrow band of purplish red color. Petals with the tips strongly asymmetric, broadly rounded with a shorter, shallowly concave, notched or single-toothed portion toward one side, the margin otherwise more or less entire, yellow to yellowish orange. Stamens numerous, the staminal column circular in cross-section, without a low crown of teeth at the tip, the anthers yellow. Pistils with 5–11 locules, the carpels arranged in a ring. Styles fused most of their length, each branch with a globose terminal stigma. Fruits schizocarps breaking into 5–12 mericarps. Mericarps 3–5 mm long, wedge-shaped, brown to dark brown, with a pair of short erect beaks toward the tip (beaks single elsewhere), the dorsal surface broadly rounded to somewhat flattened or with a shallow longitudinal groove, oblong to kidney-shaped in profile, minutely pubescent with stellate and fasciculate simple hairs toward the tip, differentiated into a sterile upper cell and a lower cell containing 1 seed, the upper sterile cell smooth-walled to finely roughened and the lower cell with a reticulate pattern of thickenings on the sides, dehiscent toward the tip between the spines. Seeds 2.0–2.5 mm long, ovate with a small notch at the tip, the surfaces glabrous, brown to dark brown. About 150 species, nearly worldwide, most diverse in tropical and warm-temperate regions.

In addition to the species treated below, S. rhombifolia L. (arrowleaf sida) may also be expected to be found in southern Missouri in the future. Like S. spinosa, this is a weedy pantropical species, and it has become naturalized in the southeastern United States as far north as northern Arkansas. It resembles S. elliottii in its more robust habit and greater number of mericarps and style branches (10–14), but has the broader leaf blades and shorter petals (4–9 mm long) more typical of S. spinosa. Sida rhombifolia differs from both of the species presently known from the state in having a single short beak toward the tip of each mericarp, which would cause problems in the key to genera of Missouri Malvaceae.