Molecular phylogenetics, floral convergence and systematics of Dichromanthus and Stenorrhynchos (Orchidaceae: Spiranthinae)

Abstract

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 non-coding 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. Bee-pollinated D. michuacanus is recovered in a derived position relative to hummingbird-pollinated Dichromanthus spp., suggesting a secondary reversal in this trait.

<span lang="EN-GB">Phylogenetic relationships of Discyphus scopulariae (Orchidaceae, Cranichideae) inferred from plastid and nuclear DNA sequences: evidence supporting recognition of a new subtribe, Discyphinae</span>

“…In both the MP and ML analyses, relationships within Spiranthinae and the various clades of Cranichidinae match closely those found in previous molecular phylogenetic analyses (e.g. Salazar et al 2003Salazar et al , 2009Salazar et al , 2011a …”

“…Molecular methods:-DNA extraction, amplification, and sequencing were carried out using standard methods and primers described in Salazar et al (2003Salazar et al ( , 2011a. In all instances, bidirectional sequencing was performed, and the chromatograms were edited and assembled with Sequencher (GeneCodes Corp.).…”

“…The nuclear region analysed was the internal transcribed spacer region of the nuclear ribosomal DNA (nrITS; Baldwin et al 1995). All these DNA regions have been used previously to infer phylogenetic relationships in Spiranthinae (Salazar et al 2003(Salazar et al , 2011aGórniak et al 2006;Salazar & Ballesteros-Barrera 2010;Batista et al 2011;Salazar & Dressler 2011;Salazar & Jost 2012), other Cranichideae (Figueroa et al 2008;Álvarez-Molina & Cameron 2009;Salazar et al 2009Salazar et al , 2011bCisternas et al 2012) and many other orchid clades (review in Cameron 2007). We were particularly interested in clarifying the relationships of Discyphus to other Spiranthinae and discussing its morphological peculiarities in light of its inferred phylogenetic position.…”

Taxonomic notes on Lyroglossa and Pteroglossa (Orchidaceae: Spiranthinae): two new generic records for the flora of Rio Grande do Sul

“…Spiranthinae has been supported as a monophyletic group in several phylogenetic studies (Salazar 2003, Figueroa et al 2008, 2009, 2011. All these studies support the existence of four clades: "Stenorrhynchos Clade", "Pelexia Clade", "Eurystyles + Lankesterella Clade" and "Spiranthes Clade".…”

“…labellum and column shape; Figure 3D) with other members of the "Stenorrhynchos Clade", mainly with Eltroplectris Raf., and this seems to indicate a closer relationship between these and other genera in this clade. Recent molecular studies (Salazar et al 2011) support such a relationship and have indicated that Pteroglossa is inserted within the "Stenorrhynchos Clade", and is closely related to Sacoila Raf., Mesadenella Pabst & Garay and Eltroplectris.…”