Molecular phylogeny of Aerides (Orchidaceae) based on one nuclear and two plastid markers: a step forward in understanding the evolution of the Aeridinae

Abstract

Phylogenetic relationships of the orchid genus Aerides (Epidendroideae, Vandeae, Aeridinae) from Southeast Asia were inferred from DNA sequences of one nuclear (nrITS) and two plastid (matK, trnL-trnL-F) regions of 48 taxa (21 Aerides, 25 other Aeridinae, 2 outgroup). Analyses of the combined datasets with parsimony, maximum likelihood and Bayesian methods revealed that Aerides is monophyletic and consists of three well-supported subclades which are only partly in accordance with previous sectional delimitations based on floral characters. The two different flower types in Aerides (hidden versus open spur entrance) seem to have evolved at least twice in geographically distinct areas. The phylogeny presented here is yet another example in Orchidaceae where floral morphology cannot be relied on to reconstruct phylogenetic history but rather is the result of pollinator-driven selection. The Aerides subclades are characterized by three different length classes of the mutation-rich P8 region in the trnL intron. To our knowledge, this is the first time that the P8 region was studied in orchids. The matK gene has been assumed to be a pseudogene in orchids due to occasional occurrence of frameshift indels, low transition/transversion (ts:tv) ratios and low substitution rates at the 3rd codon position. However, matK does not appear to be a pseudogene in Aerides and a comparison with data from other angiosperms suggests that ts:tv ratios and low substitution rates have been overestimated as arguments for a pseudogene status of matK in orchids.