Phylogeny and evolution of Orchis and allied genera based on ITS DNA variation: morphological gaps and molecular continuity

Abstract

Phylogenetic relationships among members of genus Orchis and allied genera Aceras, Anacamptis, Barlia, Dactylorhiza, Gymnadenia, Himantoglossum, Neotinea, Ophrys, Platanthera, and Serapias were inferred from nucleotide sequence variation in the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA. Sequences were subjected to various alignments by changing the gap opening and extension parameters. After a preliminary parsimony analysis, the alignment with the lowest homoplasy indicators was chosen as optimal. The phylogenetic analysis, carried out on the optimal alignment by using Gennaria as an outgroup and a total of 31 taxa, showed that all the genera considered in this study are nested in Orchis despite their distinct morphological features. Genus Orchis is divided into two major clades, each of which includes one or more of the other genera in this study. The resulting phylogenetic hypothesis does not match previous conclusions based on vegetative and floral morphology of the taxa involved but is congruent with isoenzyme, karyological, and chloroplast DNA restriction data. Our results indicate that floral morphology is highly flexible and current generic and infrageneric limits are artificial. Even if some floral characters closely correspond to the molecular data, most are highly homoplastic and thus unsuitable for phylogenetic reconstruction. Various traits pertaining to floral morphology may be interpreted as a result of ecological convergence related to pollinator-mediated selection; such characters can undergo drastic modifications without correspondingly dramatic genetic changes.