Molecular phylogenetics of Prescottiinae s.l. and their close allies (Orchidaceae, Cranichideae) inferred from plastid and nuclear ribosomal DNA sequences

The Andes are a cradle of orchid evolution, but most phylogenetic studies of Orchidaceae in this biodiversity hotspot have dealt with epiphytic epidendroid lineages. Here we present a study on neotropical, terrestrial, orchidoid taxa of Prescottiinae s.l. (8 genera, ～100 species), which are adapted to some of the highest elevation habitats on earth that support orchids. They are currently included within an expanded concept of Cranichidinae in the tribe Cranichideae, but DNA sequence data show that neither Prescottiinae s.l. nor Cranichidinae s.s. are monophyletic. Prescottiinae s.l. consist of two strongly supported lineages: the Altensteinia and Prescottia clades, which have closer affinities to Spiranthinae than to Cranichidinae. The Prescottia clade comprises two well-supported subclades, one including most sampled species of Prescottia and a second one with Pseudocranichis thysanochila sister to Prescottia tubulosa. As a group, they are sister to Spiranthinae. Sister to this pair is the Altensteinia clade comprised of six genera, whose intergeneric relationships are well resolved. Finally, Cranichidinae s.s. is sister to all three of these clades. Morphological and ecological features distinguishing the major groups are discussed, as are potential synapomorphies to define them. The reconstructed phylogeny indicates that the classification of Cranichideae needs to be reexamined.