3. Tribe Cardueae Cass.

Plants annual, biennial, or perennial herbs (rarely woody elsewhere), the sap not milky. Stems unbranched or branched, sometimes with spiny wings (from decurrent leaf bases). Leaves alternate, sometimes also in a basal rosette, frequently spiny along the margins. Leaf blades simple, commonly with marginal teeth or pinnately lobed, rarely entire. Inflorescences terminal or less commonly axillary, consisting of solitary heads at the stem or branch tips or few- to several-headed clusters (sometimes appearing as small, flat-topped panicles in Cirsium arvense). Heads entirely discoid or the marginal florets sometimes sterile, somewhat enlarged, and appearing raylike. Involucre of several overlapping series of bracts, these appressed or with a spreading tip, the tip often spiny or with an elongate bristle or flattened appendage. Receptacle flat to short-conical (fleshy in Onopordum), with numerous bristles or less commonly short scales. Disc florets perfect (the plants incompletely dioecious in Cirsium arvense) or the outermost ones sometimes sterile, somewhat enlarged, and raylike. Pappus rarely absent, sometimes of several short scales or awns, most commonly of numerous bristles, these often of different lengths, usually finely barbed or plumose (featherlike with numerous long, capillary side branches), persistent at fruiting or more commonly shed before fruiting individually or as a unit. Corollas yellow, white, pink, purple, or blue, the tube usually slender and elongate, with relatively long, sometimes asymmetrically cut, slender lobes. Stamens with the filaments not fused together (fused toward the base in Silybum), the anthers fused into a tube, each tip with a short to long, sometimes indistinct appendage, each base prolonged into a pair of slender, elongate (short in Silybum), tail-like lobes, these often hairy. Style branches usually somewhat flattened, each with a stigmatic band along the inner face, lacking a sterile tip. Fruits variously shaped, not winged, not beaked but often with a minute crown or conical projection at the tip. About 83 genera, about 2,500 species, nearly worldwide but most diverse in the Old World.

Species are mostly easily recognized as members of the Cardueae, but generic and specific distinctions within the tribe generally are more problematic. The presence of involucral bracts having the tip modified with a spine, bristle, or flattened appendage; the usually long, narrowly tubular corollas with slender lobes; and the bristly (rarely scaly) receptacle are easily observed characters that tend to mark the tribe. Interestingly, at least in the midwestern United States, those taxa having spiny wings on the stems are all nonnative. However, the group lacking this character comprises both native and introduced taxa. In many botanical works (Steyermark, 1963; Gleason and Cronquist, 1963, 1991), this tribe has been treated under the illegitimate name Cynareae (Scott, 1990).

The principal economic importance of the Cardueae is for its noxious weeds of pastures and cropland, as well as species that are invasive exotics in natural communities. However, several species provide positive economic benefits. Various species in several genera are cultivated as ornamentals. Cynara cardunculus L. (cardoon) is cultivated for its edible celery-like petioles. The closely related C. scolymus L. (artichoke, globe artichoke) is prized for the edible bracts and receptacle of immature heads (the so-called choke consists of the receptacular [chaffy] bristles and the developing florets with abundant pappus bristles).

Carthamus tinctorius L. (safflower) has long been cultivated for a number of uses. Before the development of artificial dyes, it was cultivated mostly in the Old World for its bright flowers, which were used as a dye, a colorant for cosmetics (rouge), and as a food coloring substitute for the unrelated and more costly saffron. Today, safflower is widely grown commercially for its seeds, which provide a polyunsaturated oil popular for cooking and in salad dressings. Safflower also is a constituent of many birdseed mixes, and plants occasionally are reported to the Flora of Missouri Project by curious homeowners who observe them under and near their bird feeders. Thus far, this species has not been documented to persist or reproduce itself in the wild in Missouri, and it is thus not formally treated here. Carthamus tinctorius is relatively easily distinguished from other thistles by the lower involucral bracts, which are enlarged and leaflike, and by its corollas, which most commonly are bright orange to reddish orange (less frequently yellow or red).