Molecular phylogenetics, floral convergence and systematics of Dichromanthus and Stenorrhynchos (Orchidaceae: Spiranthinae)
2011
Salazar, Gerardo A. | CABRERA, LIDIA I. | FIGUEROA, COYOLXAUHQUI
Contrasting generic concepts of Dichromanthus and Stenorrhynchos held recently by taxonomists were assessed by means of parsimony and Bayesian cladistics analyses of 40 species/22 genera of Spiranthinae and over 2400 base pairs of nonâcoding nuclear and plastid DNA. Floral structure of relevant taxa was compared using fresh, pickled and herbarium specimens. Our results indicate that a broad concept of Dichromanthus corresponds to a strongly supported monophyletic group sharing several ecogeographical attributes and at least one putative floral synapomorphy (nectary formed by a narrow channel at the base of the labellum). Dichromanthus s.l. occupies a derived position within the Spiranthes clade, with Deiregyne being strongly supported as its sister genus. Stenorrhynchos, as delimited by most previous taxonomists, is shown to be polyphyletic; monophyly requires a narrower delimitation and this narrow concept is strongly supported as belonging in the Stenorrhynchos clade, which also includes members of the genera Eltroplectris, Mesadenella, Pteroglossa and Sacoila. The scant published information on natural pollination and inferences made from flower colouration and morphology suggest convergence in floral characteristics between species of Dichromanthus, Stenorrhynchos and probably other distantly related genera as a result of independent adaptation to pollination by hummingbirds. Beeâpollinated D.âmichuacanus is recovered in a derived position relative to hummingbirdâpollinated Dichromanthus spp., suggesting a secondary reversal in this trait.â© 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 167, 1–18.
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