Abstract.: The orchid subfamily Apostasioideae consists of two genera, Apostasia and Neuwiedia. To study the position of Apostasioideae within Orchidaceae and their intra- and intergeneric relationships, a molecular phylogenetic analysis has been conducted on the nuclear ITS region and the two plastid DNA regions trnL-F intron and matK. The two genera traditionally ascribed to Apostasioideae are each monophyletic. In Apostasia, A. nuda, with two stamens and no staminode, is sister to a clade comprising three species characterised by two stamens and one staminode. Within Neuwiedia, maximum parsimony analyses place N. zollingeri as sister to the clade formed by N. borneensis and N. veratrifolia. A family-wide phylogenetic analysis of matK sequences representing all proposed subfamilies of Orchidaceae produced five moderately to well-supported clades. One of these clades, Apostasioideae, is sister to the clade formed by Vanilloideae, Cypripedioideae, Orchidoideae and Epidendroideae. High transition-transversion ratio and the absence of stop codons in the individual sequences suggest that matK is at the transition from a possibly functional gene to a pseudogene in Apostasioideae, contrary to what is found in some other groups of Orchidacea
