Apparent similarity, underlying homoplasy: Morphology and molecular phylogeny of the North American clade of Manihot.

PREMISE OF THE STUDY Morphologically diverse clades are useful for detecting adaptive morphological evolution. Each of their variants may have evolved once or several times, suggesting that their repeated appearance may be due to environmental pressures. The North American Manihot species are an excellent system to detect possible adaptations and to assess the effect of mono- or polyphyly on classification. With 20 species, this group includes growth forms from tuberous herbs to trees. The monophyly of this group and its relationship with the economically important M. esculenta were tested for the first time with complete sampling of North American species. METHODS We carried out maximum likelihood and Bayesian phylogenetic analyses on a matrix of 3662 bp from chloroplast (psbA-trnH, trnL-trnF) and nuclear loci (PEPC and two paralogous copies of G3pdh). We included all North American Manihot species, Manihotoides pauciflora, and published sequences from 34 South American species. KEY RESULTS Our results support monophyly of the North American Manihot group. Its taxonomic sections are paraphyletic, and three to four growth forms evolved repeatedly. Manihotoides pauciflora is nested within North American Manihot species. Some PEPC and G3pdh clones grouped with clones of other species and not with clones from their own species. CONCLUSIONS North and South American Manihot species are sister clades. Paraphyly of North American sections suggests that taxonomic revision is warranted. The position of Manihotoides pauciflora confirms that Manihotoides should remain subsumed within Manihot. Most growth forms likely evolved repeatedly in this group. The behavior of PEPC and G3pdhNA clones is probably due to incomplete lineage sorting.