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Several studies have reported stingless Meliponini bees gathering hairs from the labella of Maxillaria spp., including M. ochroleuca, a member of the M. splendens alliance. Such hairs usually contain food materials and are thought to have nutritional value. The papillose labella of representatives of the Maxillaria splendens alliance, however, bear scattered, simple 1-5-celled uniseriate trichomes (hairs) that lack food materials. By contrast, here, as well as polyphenolic compounds, typical labellar papillae usually contain small quantities of starch, protein, and minute droplets of lipid, the last probably involved in the production of fragrance. Towards the labellum apex occur elevated groups of papillae that lack food materials, but contain volatile compounds, probably fragrance precursors. In the past, the terms 'trichomes' or 'hairs' and 'papillae' have been used interchangeably, causing some confusion. Since the trichomes, however, unlike the papillae, are easily detachable and can fragment, it is most likely they, not the papillae, that have previously been observed being collected by bees, but their poor food content indicates that they do not function as food-hairs. Even so, our field observations of M. ochroleuca reveal that stingless bees scrape polyphenol-rich labellar tissue and possibly use this material to produce a resinous, complex, heterogeneous substance commonly referred to as 'bee glue', used for nest construction and repair. [ABSTRACT FROM AUTHOR]

Premise: Angiosperms distributed over a large geographical area may display considerable phenotypic variation that can be recognized at morphological and micromorphological levels. Here, we investigate the pollination biology and the presence of floral rewards in Brazilian populations of the widely distributed orchid, Brasiliorchis picta. Based on the new data presented here this study investigates the evolution of floral rewards in Maxillariinae, and tests for the occurrence of convergent evolution of food‐hairs in this subtribe. Methods: Micromorphological and histochemical analyses of the labellar tissues were conducted, together with chemical analysis of fragrance and experiments involving the use of chemical baits. The evolution of floral rewards in Maxillariinae were addressed. Results: Microscopy revealed that B. picta offers food‐hairs as a reward. Fragrance is produced by abaxially located labellar epidermal papillae. The main compound present in our samples (2‐phenylethanol) also occurs in the aggregation pheromone produced by the mandible glands of pollinators, Meliponini bees. Our analyses indicate a high diversity of flower rewards and pollinators displayed by members of Maxillariinae, and support that edible trichomes evolved independently five times in the subtribe. Conclusions: The high diversity of floral rewards and pollinators displayed by members of Maxillariinae suggests that different pollinator pressures are involved in the evolution of this neotropical subtribe. In addition, the offering of food‐hairs, which are generally infrequently encountered in Orchidaceae, arose by convergent evolution in Maxillariinae. [ABSTRACT FROM AUTHOR]

Barkeria scandens and B. whartoniana are endangered, endemic taxa from Mexico. They are epiphytes adapted to dry habitats. Since these plants are xerophytic, their flowers were investigated for structural adaptations to nectar secretion. The flowers of both species are structurally similar, and contrary to most claims for the genus, have functional floral nectaries comprising a nectary chamber and a narrow tubular cuniculus. Nectar is present in both these structures, and contains sugars and lipid-like compounds. The nectary tissue is composed of a single-layered epidermis overlying 1–2 layers of subepidermal secretory parenchyma. The outer tangential wall of the epidermal cells is thick and multi-layered, whereas the cuticle, which often shows blistering, is lamellate and possesses micro-channels. Lipid-like material occurs both between the microfibrils of the cell wall and in the micro-channels. Robust secretory tissue, thick cell walls, and lipid-like nectar components limit nectar evaporation. Moreover, the rigidity of the nectary potentially makes it possible for red-flowered B. scandens to switch from entomophily to ornithophily. [ABSTRACT FROM AUTHOR]

Most members of the Neotropical orchid subtribe Maxillariinae lack floral rewards (e.g. nectar, food-hairs, resin or wax) and attract pollinators by food- or sexual-deceit. Of those that produce floral rewards, relatively few produce resin. Members of the Mexican and Central American Camaridium cucullatum complex are considered to be entirely rewardless. Here, we demonstrate that they produce lipoidal or resin-like labellar secretions. They are also characterized by the possession of a prominent, and often brightly coloured, thickened transverse ridge located at the base of the column, above the point of attachment to the labellum. Although the transverse ridge is considered a putative synapomorphy for members of the C. cucullatum complex, a similar structure was observed in the related genus Nitidobulbon. Anatomy and secretory activity of the labella and presumed transverse ridges of both taxa are investigated and compared by means of light and fluorescence microscopy, in conjunction with histochemistry and scanning and transmission electron microscopy. Of the representatives of core Maxillariinae investigated, only members of the C. cucullatum complex possessed a transverse ridge, strengthening claims for this synapomorphy. The similar structure in Nitidobulbon comprised the proximal part of the column. Because both these structures were non-secretory and located in juxtaposition to the secretory region of the labellum, where their bright colours contrasted with those of the perianth segments, it is proposed that they act as focal points, guiding insect visitors further into the flower, and thus facilitating pollination. It is also hypothesized that they compensate for a lack of obvious nectar-guides on the labellum, or where these are obfuscated by heavy secretions of resin. Because the transverse ridge was not prominent in some members of the C. cucullatum complex, and not always easily distinguishable from superficially similar structures in related genera (e.g. Nitidobulbon), we recommend it be used in taxonomy only in conjunction with other more reliable characters. [ABSTRACT FROM AUTHOR]

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. [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]

Background and Aims Capanemia Barb. Rodr. comprises seven species that mostly inhabit the Brazilian Atlantic Rain Forest domain. The genus currently consists of two sections: Capanemia Cogn. and Planifolia Pabst, distinguished on the basis of leaf shape. We compare the floral morphology and anatomy of all species to determine whether separation into sections is supported by floral characters. Methods Both fresh flowers and herbarium specimens were investigated, and column and pollinarium features, together with the presence or absence of floral rewards, recorded. Anatomical features were examined using both light microscopy and scanning electron microscopy. Key Results and Conclusions With the sole exception of Capanemia therezae, all species shared a distinctive set of floral characters. Flowers were mostly white or yellowish-white and fragrant, and column wings were positioned parallel to the labellum, concealing the stigmatic cavity. Pollinaria had proportionally long tegular stipes and clavate to reniform pollinia, whereas the labellum possessed a conspicuous indument of trichomes, but was devoid of nectar or any other secretion that might function as a food-reward. Capanemia therezae, however, was exceptional in having greenish, unscented flowers with short, rounded and divergent column wings and an exposed stigmatic cavity. Its pollinaria had proportionally short tegular stipes and round pollinia, whereas the labellum lacked trichomes. Droplets of nectar were evident on the adaxial surface of the labellum, adjacent to the callus. Floral features did not support the currently accepted sectional division of Capanemia. If ongoing phylogenetic studies demonstrate that both sections are indeed monophyletic, then these taxa should be distinguished solely on the basis of foliar features. [ABSTRACT FROM AUTHOR]

Pigment stripes associated with veins (venation) is a common flower colour pattern. The molecular genetics and function of venation were investigated in the genus Antirrhinum, in which venation is determined by Venosa (encoding an R2R3MYB transcription factor). Pollinator preferences were measured by field tests with Antirrhinum majus. Venosa function was examined using in situ hybridization and transient overexpression. The origin of the venation trait was examined bymolecular phylogenetics. Venation and full-red flower colouration provide a comparable level of advantage for pollinator attraction relative to palely pigmented or white lines. Ectopic expression of Venosa confers pigmentation outside the veins. Venosa transcript is produced only in small areas of the corolla between the veins and the adaxial epidermis. Phylogenetic analyses suggest that venation patterning is an ancestral trait in Antirrhinum. Different accessions of three species with full-red pigmentation with or without venation patterning have been found. Epidermal-specific venation is defined through overlapping expression domains of the MYB (myoblastoma) and bHLH (basic Helix-Loop-Helix) co-regulators of anthocyanin biosynthesis, with the bHLH providing epidermal specificity and Venosa vein specificity. Venation may be the ancestral trait, with full-red pigmentation a derived, polyphyletic trait. Venation patterning is probably not fixed once species evolve full-red floral pigmentation. [ABSTRACT FROM AUTHOR]

Crepidium is a large genus of mainly pantropical orchids. The lips of its flowers are upwardly directed and do not serve as landing platforms for pollinators. This role is assumed by the dorsal sepal and/or gynostemium. Information about the pollination and floral morphology of this genus is scarce. To date, no papers have been published on these topics. Field observations have revealed that the flowers are visited by small flies, midges, fruit flies, other small dipterans, ants, spiders, and mites. Preliminary observations revealed at least two forms of small liquid droplets secreted on the lip surface of Crepidium species: simple secretions from epidermal cells, and cell sap released upon the rupturing of raphide-producing cells. Further research revealed that this was the first time liquid secretion was recorded in this genus. Floral secretions were subjected to sequential organic solvent extraction and gas chromatography–mass spectrometry (GC–MS). Floral parts were investigated by means of scanning (SEM) and transmission electron microscopy (TEM), and histochemical tests. The presence of liquid droplets on the lip of Crepidium, the presence of a food reward, and the sequence of raphide development are reported here for the first time. [ABSTRACT FROM AUTHOR]

Highlights: [•] New identifications of anthocyanins in the reproductive and vegetative organs of Rhabdothamnus solandri. [•] The differential accumulation of pelargonidin-based and cyanidin-based anthocyanins underlies the colour patterns observed in the bird-pollinated Gesneriaceae species. [•] Anthocyanin patterning in R. solandri is likely regulated through the differential activity of the flavonoid-3′-hydroxylase. [•] Anthocyanic vacuolar inclusions (AVIs) in the flowers suggest that basic anthocyanin structures without aromatic acylation can also form AVIs. [•] A valuable system for studying regulatory mechanisms of anthocyanins, providing new insights into ornamental breeding. [Copyright &y& Elsevier]