7. Tribe Heliantheae Cass.

Plants annual, biennial, or perennial herbs (sometimes woody elsewhere), sometimes from a woody rootstock, sometimes aromatic, occasionally monoecious, the sap not milky. Stems not spiny or prickly. Leaves alternate and/or opposite (whorled elsewhere), rarely only in a basal rosette, sessile to long-petiolate, not spiny or prickly. Leaf blades entire to lobed or pinnately compound, the venation pinnate or less commonly with 3 or more main veins. Inflorescences terminal panicles, spikes, or racemes, sometimes reduced to clusters of heads, or the heads solitary at the branch tips. Heads discoid or radiate. Involucre of 1 or 2 to more commonly several series of bracts, in a few genera these spiny or tuberculate. Receptacle flat to hemispherical or conical, naked or with chaffy bracts or hairs subtending all or some of the florets. Ray florets (when present) pistillate or sterile, sometimes inconspicuous, the corolla showy or sometimes very short or rarely absent, when present white, pink, purple, blue, yellow, or orange. Disc florets all perfect or functionally staminate, the corolla absent or highly reduced in a few monoecious genera, when present yellow, purple, purplish brown, the 4 or more commonly 5 lobes spreading to ascending. Pappus variously of numerous capillary bristles or 1 to several awns or scales, occasionally reduced to a minute crown or absent, when present persistent or not persisting at fruiting. Stamens with the filaments not fused together and the anthers fused into a tube or in a few genera with the filaments more or less fused into a tube and the anthers more or less free, each anther tip with a short to long appendage, each anther base truncate or less commonly with a pair of short lobes. Style branches somewhat flattened (the style undivided at maturity in functionally staminate flowers), each with a stigmatic line along each inner margin or more commonly with a stigmatic band along each inner surface, the sterile tip usually relatively long and tapered, less commonly short and truncate, usually with dense, minute hairs, at least on the outer surface. Fruits sometimes dimorphic (the outer series then thicker-walled and with different surface ornamentation), in a few genera enclosed in the persistent hardened involucre (forming a bur), sometimes somewhat flattened or angled to ribbed, variously shaped in profile, not beaked. About 300 genera, about 3,300 species, worldwide.

The Heliantheae are one of the largest and morphologically most diverse tribes in the family, which makes description of the tribe a challenge. The circumscription adopted here parallels that in the upcoming Asteraceae volumes of the Flora of North America series and differs from that adopted by Steyermark (1963) most notably in the inclusion of the genera that he separated as the tribe Helenieae Benth. Other recently proposed classifications, based mostly on molecular data, have varied widely, from those advocating the inclusion of the genera of Eupatorieae into a very broadly defined Heliantheae (Jansen and Kim, 1996; Bayer and Starr, 1998) to those who have suggested dissection of the Helenieae into six or more tribes in order to preserve the more traditional taxonomic circumscriptions of Heliantheae and Eupatorieae while providing formal recognition to each of the groups identified as monophyletic from the molecular data (Baldwin et al., 2002; Panero and Funk, 2002). Ultimately further research will be necessary to stabilize the limits of the Heliantheae and its sister tribes, and the present classification undoubtedly will have to be changed in the future to better reflect evolutionary relationships in the family.

A number of genera of Heliantheae contain members that are commonly cultivated as garden ornamentals and/or cut flowers, including Bidens, Coreopsis, Cosmos, Echinacea, Gaillardia, Helenium, Heliopsis, Rudbeckia, Tagetes, and Zinnia L. Helianthus is the most important crop genus, including H. annuus, the common sunflower, which is grown for its oil and seeds, as well as H. tuberosus, Jerusalem artichoke, which produces an edible tuberous root. Guizotia is the source of Niger thistle, which is a popular source of bird seed. On the negative side, a few genera contain species that are aggressive weeds of agricultural lands and producers of allergenic wind-borne pollen, including Ambrosia, Iva, and Xanthium.