Floral micromorphology of the genus Restrepia (Orchidaceae) and the potential consequences for pollination

Abstract

Restrepia is a small Pleurothallid genus, comprising 57 species, 44 of which were discovered since 1970. These species are indigenous to Central and South America, where their montane forest habitats are under increasing pressure from changes in land use. With resulting increasingly fragmented habitats and dwindling numbers, the pollination systems of obligate out-breeding genera, such as Restrepia, may no longer function efficiently which could potentially lead to their extinction. As such, the main aim of the current study was to perform an in-depth investigation of floral structures in the genus, using SEM and photographic technology to formulate a putative pollination mechanism for these species. The floral micromorphology of dorsal sepal and lateral petal osmophores, synsepal, labellum, cirrhi and calli were investigated by scanning electron microscopy (SEM), macro-photography and statistical analyses of some floral proportions. The secretory nature of the labellum, synsepal and osmophore papillae were established and the calli were shown to possess a unique papillate, non-secretory structure. A pollination mechanism for the genus was proposed which includes the role of the scent trails produced by the osmophores and the 'trapping' role of the cirrhi. A 'functional fit' between the flower and the pollinator is suggested. In conclusion, we consider Restrepia to represent a non-nectar rewarding and 'deceptive' orchid genus and that this pollination mechanism may be directly linked to the breeding system (gametophytic self-incompatibility) in this genus. Thank you for your favourable reply regarding our manuscript. Since which time, we have been addressing the minor revisions from your review. The main problem concerned entering species authorities into Table 1, about which I contacted you. We tried your suggestion to create a new table, but after due consideration found that this didn't work very well. Therefore, we decided to reformat Table I to include species authorities and have included the reference to the WCSP, (Kew) which is from where this information was obtained. Anyone wishing to check these data, should now be able to do so. All the minor text, spelling, formatting changes that you suggested were accepted via track changes. Our reponse to some of the other points you suggested for amendment are highlighted below in red. Pg 11 Line 207 eventually after consideration we decided on the following wordingWe consider them to be…… This expressed our hypothesis better, and still implied it was our idea and not proven fact Pg 12 lines 212-213 As this sentence was unclear, it has been omitted. The previous few lines, really had said everything that was required. Pg 12 lines 224-255 Comment 'thus, pollination may no longer occur during thus stage? and animals entering at this stage may not be pollinators?'The sentence has been rephrased. This seems to be an adaptation to bring about pollination if it has not occurred when senescence begins. The wording should now make this clearer. Pg 12 lines 226...

Deep in the Jelly: Histochemical and Functional Aspects of Mucilage-Secreting Floral Colleters in the Orchids Elleanthus brasiliensis and E. crinipes

“…According to the constituents of the secretion, the glandular trichomes receive a functional denomination like the nectaries (production of nectar) and the colleters (mucilage and/or lipid-like substances secretion) (Fróes et al, 2015; Tian et al, 2017). In the Orchidaceae, researchers have previously observed the presence of nectaries (Leitão et al, 2014; Pansarin et al, 2015; Solano-Gómez et al, 2016), osmophores (Pansarin and Amaral, 2009; Millner and Baldwin, 2016; Caballero-Villalobos et al, 2017), idioblasts, and colleters (Leitão and Cortelazzo, 2008; Mayer et al, 2011; Cardoso-Gustavson et al, 2014).…”

A new species of Pleurothallis (Orchidaceae: Pleurothallidinae) in subsection Macrophyllae-Fasciculatae with a unique, highly reduced, morphologically distinct labellum

“…The last two decades have seen substantial progress in the study of pollination strategies in Pleurothallidinae, including in the genera Acianthera Scheidw. (Borba & Semir 2001); Andinia (Luer) Luer (Álvarez 2011); Dracula Luer (Endara et al 2010, Policha et al 2016; Lepanthes Sw. (Blanco & Barboza 2005, Blanco & Vieira 2011, Calderón-Sáenz 2012; Restrepia Kunth (Millner & Baldwin 2016); Specklinia Lindl. (Karremans et al 2015); and Trichosalpinx Luer (Bogarín et al 2018).…”

A new species of Pleurothallis (Orchidaceae: Pleurothallidinae) from Valle del Cauca, Colombia and a note on the relationship between subsections Macrophyllae-Racemosae and Antenniferae

“…Other genera in subtribe Pleurothallidinae have been studied in much greater depth, including Anathallis (CardosoGustavson 2014), Dracula (e.g. Policha et al 2016), Lepanthes (Blanco & Barboza 2005), Octomeria (Cardoso-Gustavson 2014), Restrepia (Millner & Baldwin 2016), Specklinia (e.g. Karremans et al 2015) and Stelis (Ignowski 2015.…”