Plants annual or biennial (perennial herbs elsewhere), with taproots; sap yellow (white to orange elsewhere). Aerial stems strongly ascending, usually sparsely to moderately prickly, also somewhat glaucous. Leaves basal and alternate on the stems, the stem leaves progressively shorter toward the stem or branch tips, all sessile, at least the uppermost leaves usually with a pair of rounded auricles at the base, clasping the stem. Leaf blades moderately to deeply pinnately lobed with relatively broad, often U-shaped sinuses, the lobes variously shaped, with irregularly toothed margins, these armed with staw-colored, slender prickles, the surfaces glabrous or armed with scattered slender prickles along the main veins, glaucous, often with lighter mottling along the main veins. Flowers terminal, loose clusters (sometimes appearing as small panicles) at the stem or branch tips, sometimes reduced to a solitary flower, the flowers short- to long-stalked, the stalk erect or ascending at flowering, mostly subtended by 1 or 2 bracts, these similar in appearance to leaves but smaller, the receptacle slightly expanded at the tip but not forming a cup or disc. Sepals 3, free, shed individually as the flower opens, the body 9–18 mm long, oblong elliptic, broadly pointed at the tip, sometimes armed with prickles, also with a prominent, ascending, conic, dorsal horn near the tip. Petals 4, broadly obovate, broadly rounded and often somewhat uneven or slightly ruffled at the tip, white to pale yellow or yellow. Stamens numerous. Ovary lacking a well-differentiated style at flowering, the stigma more or less capitate, with 4–6, shallow, spreading lobes. Fruits erect or ascending, oblong-elliptic to elliptic, variously nearly truncate to angled to a sharply pointed tip, the surface usually with numerous stout, ascending prickles, these often attached to shallow nipplelike structures, also longitudinally 4–6-ribbed, dehiscing to about 1/3 of the way from the tip by valves, leaving the persistent stigma attached to a network of vascular tissue exposed around the seeds. Seeds 1.5–2.0 mm long, more or less globose but abruptly tapered to a small point at the base, the short aril inconspicuous, the surface with a prominent network of ridges and pits, brown to reddish brown, not shiny. Thirty-two species, North America, South America, Hawaii; introduced in the Old World.