Phylogenetic Analysis of Chloroplast DNA in North American Gutierrezia and Related Genera (Asteraceae: Astereae)

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Abstract
Restriction site mutations analysis using 18 restriction endonucleases for chloroplast DNA''s from North American Gutierrezia has led to a generic circumscription which is somewhat different from those previously proposed. Molecular data agree with a recent taxonomic treatment of Lane (1982, 1985), which transferred the x = 4 species from Xanthocephalum and submerged Greenella into Gutierrezia, but they do not support the submersion of the monotypic genus Thurovia. Thurovia is closely related as a sister group to Amphiachyris and should be resegregated from Gutierrezia. The study indicated that Xanthocephalum with x = 6 is very distantly related to Gutierrezia, even though Xanthocephalum has often been treated as part of Xanthocephalum-Gutierrezia complex. Xanthocephalum is, in contrast, very closely related to Grindelia, which also has a base chromosome number of x = 6. Traditional species of Gutierrezia, G. californica, G. grandis, G. microcephala, G. sarothrae, G. serotina, and G. texana, constitute a closely related cluster and are well-separated from other purported members of the genus. Gutierrezia californica s. str. and G. bracteata should be separated again as distinct species. The herbaceous species G. sericocarpa and G. sphaerocephala, appear to be the most primitive in the genus.