LEE, JOONGKU*, BRUCE G. BALDWIN, AND LESLIE D. GOTTLIEB1. Jepson Herbarium and Department of Integrative Biology, University of California, Berkeley, CA 94720. 1Section of Evolution and Ecology, University of California, Davis, CA 95616. - A molecular phylogenetic study of Stephanomeria and related North American
genera (Compositae-Lactuceae) based on 18S-26S nuclear rDNA ITS sequences
.
Phylogenetic analysis of rDNA ITS sequences shows that all of the
western North American genera of Lactuceae with a base chromosome
number of n = 8, including Stephanomeria Nutt.,
Munzothamnus P. H. Raven, and Rafinesquia Nutt.,
constitute a monophyletic group. Stephanomeria, with 17 annual
and perennial species, forms a single clade and is more closely
related to Rafinesquia than to Munzothamnus.
Munzothamnus contains a single perennial species endemic to one
of the Californian Channel Islands and has been previously placed both
within Stephanomeria and within Malacothrix; our results
suggest it is an ancient lineage best recognized as a distinct genus.
Rafinesquia contains two annual species in California and the
adjacent deserts and its close relationship to Stephanomeria
was not previously recognized. The results also show that
Stephanomeria spinosa (Nutt.) Tomb, which was
transferred to Stephanomeria from Lygodesmia D. Don, is
the sister group of either Rafinesquia or Stephanomeria
or both and probably is best treated as a monotypic genus,
Pleiacanthus Rydb. Two perennial species, Stephanomeria
pauciflora (Torr.) A. Nelson and the tetraploid S.
parryi A. Gray, are closely related to each other and appear to
be more closely related to the six annual species than to the other
perennials.
Key words: Asteraceae, Compositae, ITS, Lactuceae, Phylogeny, Stephanomeria