Phylogenetics of Arethuseae (Orchidaceae) based on plastid matK and rbcL sequences

Circumscriptions of Arethuseae have varied since the tribe was first descri bed by John Lindley in 1840, containing over ninety genera among the differ ent authors. The latest system of Arethuseae defined by Dressler, including around thirty genera, is the most commonly accepted today. The goals of th is study are to assess whether Arethuseae sensu Dressler and component subt ribes are monophyletic and evaluate the position(s) of Arethuseae within Or chidaceae. Sequences of two plastid genes, matK and rbcL, have been obtaine d for 24 representative genera of Arethuseae in Dressler's latest two taxon omic systems for the tribe, plus 46 other genera throughout Orchidaceae. Bo th separate and combined analyses of the matK and rbcL data indicate that t he tribe may not be monophyletic, which is also true for most subtribes wit hin Arethuseae. Furthermore, matK data suggest that this gene may be non-fu nctional within Orchidaceae.