Results of phylogenetic analyses of nuclear 18S–26S rDNA internal transcribed spacer (ITS) region sequences for representatives of most genera of helenioid Heliantheae and various members of Heliantheae s.s. (sensu stricto) and Eupatorieae help to clarify major lineages and relationships in the clade corresponding to Heliantheae s.l. (sensu lato) and Eupatorieae. Most subtribes of helenioid Heliantheae as circumscribed by Robinson (1981) correspond closely with ITS clades. Polygeneric subtribes of helenioid Heliantheae that appear to be monophyletic based on ITS data include Flaveriinae sensu Turner and Powell (1977), Madiinae sensu Carlquist (1959), and Peritylinae sensu Robinson (1981). Chaenactidinae sensu Robinson (1981) is polyphyletic, but most members of the group are encompassed within only four ITS clades. Based on the ITS data and results of combined analyses of ITS variation plus previously published morphological and chloroplast DNA data, we conclude that Heliantheae s.s. and Eupatorieae represent nested clades within helenioid Heliantheae, as previously suggested. Loss of paleae appears to have been a rare occurrence during radiation of Heliantheae s.s.; only one epaleate taxon that we sampled (Trichocoryne) was placed within an ITS clade of otherwise paleate taxa, referable to Heliantheae s.s. We conclude that expression of paleae in Heliantheae s.s., Madiinae, and Marshallia is homoplasious. We also conclude that pappi of bristles or bristle-like subulate scales have arisen in various lineages of Heliantheae s.l. and in general have received too much weight in previous circumscriptions of suprageneric taxa. Multiple examples of extreme dysploidy from high (putatively polyploid) ancestral chromosome numbers in helenioid Heliantheae are evident from the phylogenetic data. Bidirectional ecological shifts between annual and perennial habits and repeated origins of woodiness from herbaceous ancestors also can be concluded for helenioid Heliantheae. Based on modern distributions of taxa and evident phylogenetic patterns, Baeriinae, Madiinae, and the x = 19 “arnicoid” taxa probably share a common Californian ancestry. To produce a tribal taxonomy for Heliantheae s.l. that better reflects phylogenetic relationships, Eupatorieae and (provisionally) Heliantheae s.s. are retained in essentially the traditional senses, Helenieae is recognized in a restricted sense, Madieae and Tageteae are expanded, and three new tribes (Bahieae, Chaenactideae, and Perityleae) are erected. In Madieae, three new subtribes (Arnicinae, Hulseinae, and Venegasiinae) are recognized, in addition to Baeriinae and Madiinae. In Peritylinae, a new combination, Perityle montana, is proposed for Correllia montana.

Communicating Editor: Richard Jensen