Data from: Floral convergence in Oncidiinae (Cymbidieae; Orchidaceae): an expanded concept of Gomesa and a new genus Nohawilliamsia

BACKGROUND: Floral morphology, particularly the angle of lip attachment to
the column, has historically been the fundamental character used in
establishing generic limits in subtribe Oncidiinae (Orchidaceae), but it
has also been long recognized that reliance on this character alone has
produced a highly artificial set of genera. In essence, lip/column
relationships reflect syndromes associated with pollinator preferences;
most genera of Oncidiinae as previously defined have consisted of a single
floral type. Here, the degree to which this has influenced generic
delimitation in Brazilian members of the largest genus of Oncidiinae,
Oncidium, which previous molecular (DNA) studies have demonstrated to be
polyphyletic, is evaluated. METHODS: Phylogenetic analyses of the
following multiple DNA regions were used: the plastid psbA-trnH intergenic
spacer, matK exon and two regions of ycf1 exon and nuclear ribosomal DNA,
comprised of the two internal transcribed spacers, ITS1 and ITS2, and the
5·8S gene. Results from all regions analysed separately indicated highly
similar relationships, so a combined matrix was analysed. KEY RESULTS:
Nearly all species groups of Brazilian Oncidium are only distantly related
to the type species of the genus, O. altissimum, from the Caribbean. There
are two exceptions to this geographical rule: O. baueri is related to the
type group and O. orthostates, an isolated species that lacks the defining
tabula infrastigmata of Oncidium, is not exclusively related to any
previously described genus in the subtribe. Several well-supported
subclades can be observed in these results, but they do not correspond
well to sections of Oncidium as previously circumscribed or to segregate
genera as defined by several recent authors. In spite of their floral
differences, these groups of Oncidium, formerly treated as O. sections
Barbata, Concoloria pro parte, Crispa, Ranifera, Rhinocerotes, Rostrata
(only O. venustum), Synsepala, Verrucituberculata pro parte and Waluewa,
form a well-supported clade with Gomesa (including Rodrigueziella and
Rodrigueziopsis) embedded in it. Two often recognized segregate genera,
Baptistonia and Ornithophora, and the recently described Carriella are
also embedded within the Brazilian clade. The level of variation within
major subclades of the Gomesa clade is low and similar to that observed
within other genera of Oncidiinae. CONCLUSIONS: Convergence on a
stereotypical syndrome of floral traits associated with pollination by
oil-collecting bees has resulted in these characters not being reliable
for producing monophyletic taxa, and the genus Oncidium, defined by these
characters, is grossly polyphyletic. Vegetative and a few
floral/inflorescence characters link these taxa with a mainly Brazilian
distribution, and they were all transferred to Gomesa on this basis rather
than separated from Gomesa based on their floral differences, which we
hypothesize to be simple shifts in pollination strategies. Other authors
have described a large number of new genera for these former members of
Oncidium, but most of these are not supported by the results presented
here (i.e. they are not monophyletic). A new genus, Nohawilliamsia, is
described for O. orthostates because it does not fit in any currently
recognized genus and is only distantly related to any other member of
Oncidiinae.