Phylogenetic Position of Titanotrichum oldhamii (Gesneriaceae) Inferred From Four Different Gene Regions

Titanotrichum oldhamii has been variously placed in Gesneriaceae or Scrophulariaceae, although most recent taxonomic treatments treat it as a monotypic tribe within Gesneriaceae. In this study, we reconstructed a broad-scale phylogeny containing Titanotrichum using gene sequences from four sequence regions (chloroplast trnL-F intron and spacer and atpB-rbcL spacer, nuclear 26S ribosomal DNA, and the low-copy developmental gene CYCLOIDEA, CYC). The phytogenies inferred from each individual data set and the combined data are congruent in placing Titanotrichum inside Gesneriaceae. The phylogenetic tree based on combined chloroplast and nuclear DNA sequences grouped Titanotrichum with subfamilies Gesnerioideae (New World) and Coronantheroideae (South Pacific and Chile). We have isolated CYC, from most of the species of Gesneriaceae and Scrophulariaceae represented in this study, and this gene phylogeny suggests the same placement of Titanotrichum. CYC was found to evolve three times faster than the trnL-F intron and spacer, 3.3 times faster than the atpB-rbcL spacer, and eight times faster than nuclear 26S rDNA. Although there is considerable phylogenetic information in this fast evolving gene, analysis is problematic because of high levels of homoplasy and paralogy. In addition to a duplication predating a split between New World and Old World taxa (Gcyc1 vs. Gcyc2), there are several subsequent lineage-related duplications (mainly within Gcyc1).