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Floral food-rewards of B ulbophyllum range from nectar to protein-rich mucilage and lipid-rich labellar secretions. For the first time, the structure of the labellum and the secretory process are investigated for four African B ulbophyllum species. The most specialized type of labellar organization occurred in B . schinzianum, the deep, narrow, median longitudinal groove consisting of palisade-like secretory cells flanked by trichomes containing lipid droplets, and the copious secretion containing sugar. This groove was absent or poorly defined, shallow and wide, in the remaining taxa, the scant secretion containing lipid. All taxa possessed a striate cuticle lacking cracks and pores, and micro-channels were present, cuticular blisters occurring only in B . schinzianum. The labellum contained storage parenchyma ( B . lupulinum) or mesophyll-like parenchyma ( B . schinzianum), but in section M egaclinium ( B . falcatum and B . maximum), these were replaced by aerenchyma. In B . schinzianum, the form of the labellar groove, sweet fragrance and sugary secretion suggest pollination by Hymenoptera, the food-reward and fragrance indicating that pseudocopulation is unlikely. Conversely, the form of the labellum of taxa having smaller flowers, and the lipid-rich secretion, suggests pollination by small flies. The labellar aerenchyma may facilitate this process or even aid wind-assisted pollination. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 266-287. [ABSTRACT FROM AUTHOR]

Most species of Maxillaria s.l. are rewardless and employ deceit pollination strategies. Some, however, reward pollinators with nectar, resins or pseudopollen (farina). Pseudopollen is yellow-white in colour and is usually composed of food-laden cells formed by detachment or fragmentation of moniliform labellar hairs. As the pollen of epidendroid orchids is bound in pollinia, it is not accessible to pollen-foraging insects. It has thus been proposed that potential insect pollinators, deceived by the resemblance of pseudopollen to the nutritious, powdery pollen of other angiosperms, gather it and feed it to their larvae. Mimicry here, however, may not be as simple as supposed. This study compares the pseudopollen of selected species of Maxillaria s.s., namely Maxillaria grandis, M. grayi, M. huebschii and M. roseola (all members of the M. grandiflora complex), M. lepidota ( M. arachnites complex) and M. buchtienii ( M. splendens complex), using light microscopy ( LM), fluorescence microscopy, histochemistry, scanning electron microscopy ( SEM) and transmission electron microscopy ( TEM), and comments on its evolutionary significance. Some members of the M. grandiflora complex produce pseudopollen-forming hairs, the cells of which contain potential food rewards in the form of an intravacuolar protein body and abundant starch grains. Others produce pseudopollen that is devoid of protein bodies, but contains abundant starch, and others produce pseudopollen that lacks protein bodies and contains negligible amounts of starch. Maxillaria lepidota and M. buchtienii fall into the second and third categories, respectively. Lipid droplets, when present, usually occur in minute quantities. These observations suggest that a dual deceit strategy operates in some species, as pseudopollen not only mimics powdery pollen, but in many instances lacks a food reward. Cryptic evolutionary changes to pseudopollen content may confer biological advantage by reducing expenditure of material and energy in food reward production, while trichome micromorphology simultaneously encourages pollinator visits. The presence or absence of particular foods may, in turn, result in pollinator selection. Conversely, in the absence of food rewards, insect behaviour is unlikely to be reinforced, possibly to the detriment of the orchid. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173, 744-763. [ABSTRACT FROM AUTHOR]

Flowers of most species formerly included in Maxillaria are rewardless. Some, however, reward pollinators with nectar or pseudopollen, whereas the labella of a relatively small number of taxa produce lipoidal floral rewards that include resins and waxes. To date, the labellar secretory tissues of few species have been examined in detail, and some rewardless species having glossy labella are thought to mimic taxa that produce lipoidal rewards. Here, the labellar anatomy of a range of resin-secreting, wax-secreting and putative resin-mimic species is compared using light microscopy, fluorescence microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry, in order to investigate how such secretory tissues may have evolved. Comparisons are also made with other resiniferous and wax-secreting Maxillariinae s.s., and with rewardless control species and the oil-secreting elaiophores of certain Oncidiinae. The labella of all Maxillariinae species investigated displayed similar anatomy, the differences largely being restricted to the adaxial epidermis and subepidermal layer. The labellar secretory epidermis of resiniferous Maxillariella elatior was composed of epithelial palisade cells, whereas that of other resin- and wax-secreting species investigated consisted of secretory papillae or trichomes. Putative resin-mimic species also produced resin, albeit in small quantities, and, here, the epidermal cells were cuboidal or rectangular in section. Secreted material on the labellar surface of control species was probably fragrance residues. Resin was often heterogeneous, and fluorescence microscopy revealed that its composition could change throughout the course of anthesis. Although the resiniferous floral tissues of Maxillariinae s.s. may be epithelial or trichomal, and thus closely resemble the epithelial and trichomal elaiophores of oil-secreting Oncidiinae, they differ in a number of important ways, necessitating the use of more exact descriptive terminology when distinguishing between oil-, resin- and wax-secreting floral structures. Similarity between the resin- or wax-secreting floral structures of Maxillariinae s.s and the oil-secreting elaiophores of Oncidiinae is probably a result of parallelism. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 405-435. [ABSTRACT FROM AUTHOR]