BALDWIN, BRUCE G.* AND BRIDGET L. WESSA. Jepson Herbarium and Department of Integrative Biology, University of California, Berkeley, CA 94720. - Molecular phylogenetic evidence for major lineages of helenioid Heliantheae (Compositae).
Results of phylogenetic analyses of nuclear 18S-26S rDNA ITS-region
sequences for representatives of all but four recognized genera of
helenioid Heliantheae (i.e., Helenieae s. lat.) and various members of
Heliantheae s. str. and Eupatorieae help to clarify major lineages in
the clade corresponding to Heliantheae s. lat. plus Eupatorieae. Most
subtribes of helenioid Heliantheae 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 s. Turner and Powell (1977), Madiinae s. Carlquist
(1959), and Peritylinae s. Robinson (1981). Chaenactidinae s.
Robinson (1981) is polyphyletic but most members of the group are
encompassed within only four ITS clades. Based on the ITS data,
Heliantheae s. str. and Eupatorieae represent clades nested among
clades of helenioid Heliantheae, as previously suggested. Loss of
receptacular bracts appears to have occurred rarely during radiation
of Heliantheae s. str.; only one of the epaleate taxa that we sampled
(Trichocoryne) was placed within the ITS clade corresponding to
Heliantheae s. str., a principally paleate group. We conclude that
receptacular bracts were acquired independently in the ancestors of
Heliantheae s. str. and Madiinae. We also conclude that pappi of
bristles have evolved in various lineages of helenioid Heliantheae and
often have received too much weight in circumscriptions of
suprageneric taxa. Multiple examples of extreme dysploidy from high
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 must be concluded for helenioid Heliantheae. Based on
modern distributions of taxa and evident phylogenetic patterns, the
most recent common ancestor of Heliantheae s. lat. and Eupatorieae
probably occurred in southwestern North America (including northern
Mexico). Baeriinae, Madiinae, and the x = 19
"arnicoid" taxa may share a common Californian ancestry.
Key words: Asteraceae, Compositae, Helenieae, Heliantheae, ITS, Phylogeny