Relationships and evolution of matK in a group of leafless orchids (Corallorhiza and Corallorhizinae; Orchidaceae: Epidendroideae).

Corallorhizinae are a small group of Old and New World temperate orchids of which a core monophyletic group comprises Govenia, Cremastra, Aplectrum, Oreorchis and the leafless Corallorhiza, and which according to phylogenetic analysis of nuclear ITS and plastid matK sequences, are related in this way: (Govenia (Cremastra (Aplectrum (Oreorchis (Corallorhiza))))). This hypothesis is consistent with the progressive deletion of the trnK intron and matK ORF. Frameshift-resulting indels yield a predicted loss of translation for the critical "domain X" region of matK and are evidence that matK is a probable pseudogene in Aplectrum, Oreorchis, and Corallorhiza. Within Corallorhiza, a previous hypothesis based on plastid DNA restriction site analysis is confirmed, with the thickened-labellum C. striata group being sister to the thin-labellum remainder of the genus, within which the circumboreal C. trifida is sister to the remainder, which then comprise two further sister groups: C. maculata + C. bulbosa + C. mertensiana and C. odontorhiza + C. wisteriana. A close relationship between C. striata and the recently described Appalachian C. bentleyi is shown; in particular, C. bentleyi is more closely allied to a southern Mexican population of C. striata than it is to northern North American C. striata populations, suggesting that two lineages, each with Mexican and northern North American populations, exist within the C. striata group.