Comparative floral micromorphology and the ultrastructural basis of fragrance production in pseudocopulatory Mormolyca s.s. and non-pseudocopulatory Maxillaria section Rufescens s.s. (Orchidaceae)

Species traditionally considered to constitute the non-pseudocopulatory Maxillaria section Rufescens have recently been transferred to the pseudocopulatory genus Mormolyca, based on molecular phylogenetic analysis. The labellum of species assigned to the latter taxon, however, differs from that of species assigned to Maxillaria section Rufescens s.s. on morphological, anatomical, biochemical and ultrastructural grounds. Thus, whereas species of Mormolyca s.s. have insectiform, pilose-hirsute labella, the trichomes of which produce no food-reward and no resin, the non-insectiform labella of species of Maxillaria section Rufescens s.s. are papillose and their clavate papillae secrete copious resin and are frequently rich in starch. Furthermore, fragrance production in these two groups appears to involve a different set of organelles, with resin and fragrance seemingly produced by the same organelles in Maxillaria section Rufescens s.s. All these differences are ultimately related to the dissimilar pollination syndromes of the two taxa.