BATEMAN, RICHARD M.1* and PETER M. HOLLINGSWORTH2. 1Department of Botany, Natural History Museum, Cromwell Road, London, SW7 5BD, UK; 2Royal Botanic Garden, Inverleith Row, Edinburgh, EH3 5LR, UK. - Phylogenetics of Tribe Orchideae (Orchidaceae).
Internal Transcribed Spacer (rDNA) data have been obtained from 193
terrestrial orchid species, encompassing all genera and the great
majority of the widely recognized species of Orchidinae, a
heterogeneous selection of species of Habenariinae, and a single
Diseae outgroup. The resulting parsimony-based phylogeny reveals 11
well-resolved clades within Orchidinae and confirms the triphyly of
Orchis s.l. Relationships within Habenariinae are more ambiguous; the
subtribe appearing weakly monophyletic or paraphyletic according to
the tree-building algorithm used, though the genus Habenaria is
clearly highly polyphyletic. Species-level relationships are
satisfactorily resolved within most of the major clades, the
exceptions being widely recognized as taxonomically 'critical' groups such as Serapias,
derived Ophrys, and the former genus 'Nigritella'.
Relationships among the 11 major clades are less clear, and are currently being further
investigated by combining ITS with new trnL sequence data for a carefully selected subset of
63 species. Current phylogenies support the recently recognized 2n = 36 clade; they also
indicate a 2n = 40 clade that is further diagnosed by digitate root-tubers, and is derived
relative to the basally divergent clade of exclusively Asian genera. This Asian clade
identifies the plesiomorphic chromosome number as 2n = 42, and is consistent with possible
southeast Asian origins of several of the more basally divergent major clades within the
subtribe and of the subtribe itself, though ambiguous phylogenetic placements of the
potentially pivotal African genera Stenoglottis and Brachycorythis also permit
an African origin. Morphological characters informally 'mapped' across the molecular
phylogeny and showing appreciable levels of homoplasy include floral and vegetative
pigmentation, flower shape, leaf posture, gynostemium features, and various pollinator
attractants. Brief scenarios, some adaptive and others non-adaptive, are postulated for
specific evolutionary transitions.
Key words: ITS, karyotype, morphology, Orchidaceae, Orchideae, trnL