10. Tribe Senecioneae Cass.

Plants annual, biennial, or perennial herbs (woody or succulent elsewhere), the sap not milky. Stems not spiny or prickly. Leaves alternate, often also with a basal rosette, not spiny or prickly. Leaf blades simple or less commonly compound, entire to variously toothed and/or lobed. Inflorescences mostly terminal panicles or the stem branches with a small cluster or a solitary head at the tip. Heads entirely discoid or radiate. Involucre of a single series of bracts of similar size and length, these usually appressed, sometimes fused laterally, not spiny or tuberculate, usually subtended by a group of often shorter, narrow bracts. Receptacle flat to slightly convex (sometimes with a minute, nipplelike or beaklike central outgrowth), naked. Ray florets (when present) pistillate; the pappus of numerous capillary bristles, these occasionally finely barbed, usually shed individually before the fruit is dispersed; the corollas yellow. Disc florets perfect (the outermost ones in discoid taxa occasionally only staminate); the pappus of numerous capillary bristles, these occasionally finely barbed, usually shed individually before the fruit is dispersed; the corollas yellow, white, cream-colored, or pink, the tube usually expanded above the midpoint, the 5 short lobes spreading to ascending. Stamens with the filaments not fused together, the anthers fused into a tube, each tip with a short, often indistinct appendage, each base truncate or with a pair of short lobes. Style branches usually somewhat flattened, each with a stigmatic line along each inner margin or these sometimes fused into a single band, the sterile tip usually truncate, minutely hairy. Fruits mostly angled or with longitudinal lines, not winged, not beaked. About 120 genera, about 3,200 species, worldwide.

A number of members of the Senecioneae are cultivated as garden ornamentals or for cut flowers. In addition to the genera growing wild in Missouri, examples include some species of Pericallis D. Don (cineraria), Ligularia Cass. (ligularia, leopard plant), Petasites Mill. (butterbur, winter heliotrope), and Tussilago L. (coltsfoot). Most members of the tribe produce pyrrolizidine alkaloids and are considered poisonous to humans and livestock.

Circumscriptions of the two larger, traditionally recognized genera represented in the Missouri flora, Cacalia and Senecio, have been altered in recent years following studies showing that some species groups within each of these genera were less closely related to each other than they were to other genera of Senecioneae (Bremer, 1994; Barkley, 1999). Application of the generic name Cacalia L. has been particularly problematic, and its use for any group of species has been officially rejected under the International Code of Botanical Nomenclature (Greuter et al., 2000). The Missouri species are now treated under the names Arnoglossum and Hasteola. The limits of Senecio, formerly the largest genus of Asteraceae with about 3,000 species, are still subject to reinterpretation. Presently, the genus is thought to include about 1,300 mostly Old World species, but it still comprises a large number of morphologically diverse species groups. The native Missouri species are treated within the segregate genus, Packera.