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1.  Floral elaiophores in Lockhartia Hook. (Orchidaceae: Oncidiinae): their distribution, diversity and anatomy 
Annals of Botany  2013;112(9):1775-1791.
Background and Aims
A significant proportion of orchid species assigned to subtribe Oncidiinae produce floral oil as a food reward that attracts specialized bee pollinators. This oil is produced either by glabrous glands (epithelial elaiophores) or by tufts of secretory hairs (trichomal elaiophores). Although the structure of epithelial elaiophores in the Oncidiinae has been well documented, trichomal elaiophores are less common and have not received as much attention. Only trichomal elaiophores occur in the genus Lockhartia, and their distribution and structure are surveyed here for the first time.
Flowers of 16 species of Lockhartia were studied. The location of floral elaiophores was determined histochemically and their anatomical organization and mode of oil secretion was investigated by means of light microscopy, scanning electron microscopy and transmission electron microscopy.
Key Results and Conclusions –
All species of Lockhartia investigated have trichomal elaiophores on the adaxial surface of the labellum. Histochemical tests revealed the presence of lipoidal substances within the labellar trichomes. However, the degree of oil production and the distribution of trichomes differed between the three major groups of species found within the genus. All trichomes were unicellular and, in some species, of two distinct sizes, the larger being either capitate or apically branched. The trichomal cuticle was lamellate, and often appeared distended due to the subcuticular accumulation of oil. The labellar trichomes of the three species examined using transmission electron microscopy contained dense, intensely staining cytoplasm with apically located vacuoles. Oil-laden secretory vesicles fused with the plasmalemma and discharged their contents. Oil eventually accumulated between the cell wall and cuticle of the trichome and contained electron-transparent profiles or droplets. This condition is considered unique to Lockhartia among those species of elaiophore-bearing Oncidiinae studied to date.
PMCID: PMC3838557  PMID: 24169595
Anatomy; callus; elaiophore; Lockhartia; oil secretion; Oncidiinae; Orchidaceae; trichomes
2.  Comparative anatomy of the floral elaiophore in representatives of the newly re-circumscribed Gomesa and Oncidium clades (Orchidaceae: Oncidiinae) 
Annals of Botany  2013;112(5):839-854.
Background and Aims
Recently, molecular approaches have been used to investigate the phylogeny of Oncidiinae. This has resulted in the transfer of taxa previously considered to be species of Oncidium Sw. into Gomesa R. Br. and the re-circumscription of both genera. In this study, the structure of the floral elaiophore (oil gland) is described and compared for Gomesa echinata (Barb. Rodr.) M.W. Chase & N.H. Williams, G. ranifera (Lindl.) M.W. Chase & N.H. Williams, Oncidium amazonicum (Schltr.) M.W. Chase & N.H. Williams and O. oxyceras (Königer & J.G. Weinm.) M.W. Chase & N.H. Williams in order to determine whether phylogenetic revision is supported by differences in its anatomy.
The floral elaiophore structure was examined and compared at three developmental stages (closed bud, first day of anthesis and final stage of anthesis) for all four species using light microscopy, fluorescence microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry.
Key results
In all species investigated, the floral elaiophore occurs on the labellar callus and is of the epithelial type, comprising cuboidal to palisade-like, secretory epidermal cells and a layer of sub-epidermal cells, both tissues enclosing ground parenchyma supplied with collateral vascular bundles and containing idioblasts, often with raphides or phenolic contents. A bi-layered cuticle comprising an outer, lamellate and an inner, reticulate layer is present, and sub-cuticular accumulation of secreted material results in distension of the cuticle. Secretion-filled cavities are present at anthesis in the elaiophore cell walls and, in most species, the outer, tangential walls of the elaiophore have small, peg-like projections that protrude into the cytoplasm. In all taxa examined, the elaiophore organelle complement, especially the smooth endoplasmic reticulum (SER), is typical of lipid-secreting cells.
In terms of location, morphology, anatomy and ultrastructure, the floral elaiophores of both Gomesa and Oncidium species examined are very similar, and distinction between these genera is not possible based on elaiophore features alone. Furthermore, many of these elaiophore characters are shared with representatives of other clades of Oncidiinae, including the Ornithocephalus clade. Consequently, elaiophores are considered homoplasious and of limited value in investigating the phylogeny of this subtribe.
PMCID: PMC3747802  PMID: 23884394
Anatomy; elaiophore; lipid secretion; micromorphology; oil glands; Oncidiinae; ultrastructure
3.  Floral features, pollination biology and breeding system of Chloraea membranacea Lindl. (Orchidaceae: Chloraeinae) 
Annals of Botany  2012;110(8):1607-1621.
Background and Aims
The pollination biology of very few Chloraeinae orchids has been studied to date, and most of these studies have focused on breeding systems and fruiting success. Chloraea membranacea Lindl. is one of the few non-Andean species in this group, and the aim of the present contribution is to elucidate the pollination biology, functional floral morphology and breeding system in native populations of this species from Argentina (Buenos Aires) and Brazil (Rio Grande do Sul State).
Floral features were examined using light microscopy, and scanning and transmission electron microscopy. The breeding system was studied by means of controlled pollinations applied to plants, either bagged in the field or cultivated in a glasshouse. Pollination observations were made on natural populations, and pollinator behaviour was recorded by means of photography and video.
Key Results
Both Argentinean and Brazilian plants were very consistent regarding all studied features. Flowers are nectarless but scented and anatomical analysis indicates that the dark, clavate projections on the adaxial labellar surface are osmophores (scent-producing glands). The plants are self-compatible but pollinator-dependent. The fruit-set obtained through cross-pollination and manual self-pollination was almost identical. The main pollinators are male and female Halictidae bees that withdraw the pollinarium when leaving the flower. Remarkably, the bees tend to visit more than one flower per inflorescence, thus promoting self-pollination (geitonogamy). Fruiting success in Brazilian plants reached 60·78 % in 2010 and 46 % in 2011. Some pollinarium-laden female bees were observed transferring pollen from the carried pollinarium to their hind legs. The use of pollen by pollinators is a rare record for Orchidaceae in general.
Chloraea membrancea is pollinated by deceit. Together, self-compatibility, pollinarium texture, pollinator abundance and behaviour may account for the observed high fruiting success. It is suggested that a reappraisal and re-analysis of important flower features in Chloraeinae orchids is necessary.
PMCID: PMC3503500  PMID: 23071217
Breeding system; Chloraea membrancea; Chloraeinae; Halictidae; Orchidaceae; orchids; pollination
4.  Floral elaiophore structure in four representatives of the Ornithocephalus clade (Orchidaceae: Oncidiinae) 
Annals of Botany  2012;110(4):809-820.
Background and Aims
A significant number of species assigned to the Neotropical orchid sub-tribe Oncidiinae reward insect pollinators with oil produced in floral glands termed elaiophores. The latter may be glabrous (epithelial elaiophores) or hirsute (trichomal elaiophores). Although the detailed anatomy and ultrastructure of epithelial elaiophores have been studied for a number of genera, such as Oncidium Sw., Gomesa R. Br. and Trichocentrum Poepp. & Endl., hitherto, trichomal elaiophores have been investigated only for a single species of Oncidiinae, Ornithocephalus ciliatus Lindl. Furthermore, this is the only representative of the Ornithocephalus clade to be investigated to date. Here, an examination is made of the elaiophore anatomy and ultrastructure of a further four species currently assigned to this clade (Ornithocephalus gladiatus Hook., Phymatidium falcifolium Lindl., Zygostates grandiflora (Lindl.) Mansf. and Zygostates lunata Lindl.) and the results compared with those obtained for other Oncidiinae.
Elaiophore structure was examined for all species at three stages of flower development: closed bud, first day of anthesis and final stage of anthesis, using light microscopy, fluorescence microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry.
Key Results
Elaiophores of O. gladiatus occur upon the lateral lobes of the labellum and display characters intermediate between those of typical epithelial and trichomal elaiophores, in that they are largely glabrous, consisting mainly of cuboidal epidermal cells, but bear short, unicellular hairs proximally. By contrast, the elaiophores of all the other species investigated occur on the callus and are of the trichomal type. In P. falcifolium, these unicellular hairs are capitate. In all species, oil secretion commenced at the closed floral bud stage. Ultrastructurally, the mainly trichomal elaiophores of the four representatives of the Ornithocephalus clade closely resembled the epithelial elaiophores of other Oncidiinae, in that their cells displayed an organelle complement typical of lipid-secreting cells. However, in some taxa, a number of noteworthy characters were present. For example, the elaiophore cuticle of O. gladiatus and P. falcifolium was bi-layered, the outer layer being lamellate, the inner reticulate. The cuticle of Z. grandiflora and Z. lunata was also lamellate, but here, a reticulate layer was absent. Accumulation of secreted oil resulted in the localized distension of the cuticle. Cuticular cracks and pores, however, were absent from all species. The walls of the secretory cells of Z. grandiflora were also atypical in that they had short protuberances or ingrowths, and contained cavities which are thought to be involved in the secretory process.
Of the species investigated, most displayed similar anatomical organization, their trichomal elaiophores occurring on the labellar callus. They, thus, differ from many other members of the Oncidiinae, where epithelial elaiophores are found either on the callus, or on the lateral lobes of the labellum. However, ultrastructurally, all elaiophores, whether those of representatives of the Ornithocephalus clade, or those of other oil-secreting Oncidiinae, possessed a similar complement of organelles, regardless of whether the elaiophores were trichomal or epithelial. In view of the latter, and the similar chemical composition of oils derived from all Oncidiinae investigated to date, it is probable that position and type of elaiophore, and possibly the structure of the overlying cuticle, play an important role in pollinator selection in these oil-secreting orchids.
PMCID: PMC3423815  PMID: 22805528
Anatomy; elaiophore; histochemistry; lipid secretion; micromorphology; oil glands; Oncidiinae; trichome; ultrastructure
5.  A comparative survey of floral characters in Capanemia Barb. Rodr. (Orchidaceae: Oncidiinae) 
Annals of Botany  2011;109(1):135-144.
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.
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.
PMCID: PMC3241572  PMID: 21937482
Anatomy; column; labellum; morphology; nectary; orchids; pollinarium; pollination; trichomes
6.  Comparative labellar micromorphology of Zygopetalinae (Orchidaceae) 
Annals of Botany  2011;108(5):945-964.
Background and Aims
Molecular evidence indicates that the Neotropical sub-tribe Zygopetalinae is sister to Maxillariinae. Most members of the latter sub-tribe have deceit pollination strategies, but some species produce rewards such as nectar, pseudopollen, resin and wax, and are pollinated by a range of pollinators that include stingless bees (Meliponini), wasps and hummingbirds. By contrast, relatively little is known about the pollination of Zygopetalinae species. However, some are pollinated by fragrance-gathering, male euglossine bees or employ nectar deceit strategies. The aim of this study is to describe the labellar micromorphology of Zygopetalinae and to compare it with that of Maxillariinae sensu lato (s.l.) as part of an ongoing project to record the range of labellar characters found within the tribe Maxillarieae, and to assess whether these characters represent synapomorphies or homoplasies resulting from similar pollination pressures.
The labella of 31 species of Zygopetalinae, including Cryptarrhena R. Br. and representatives of the Zygopetalum, Huntleya and Warrea clades, were examined using light microscopy and scanning electron microscopy, and the range of labellar characters was recorded. These characters were subsequently compared with those of Maxillariinae s.l. which formed the subject of our previous investigations.
Key Results and Conclusions
The labellar micromorphology of Zygopetalinae is less diverse than that of Maxillariinae and does not reflect the currently accepted phylogeny of the former sub-tribe based on molecular studies. Instead, the relative uniformity in labellar micromorphology of Zygopetalinae is probably due to homoplasies resulting from similar pollinator pressures. Labellar trichomes are relatively uncommon in Zygopetalinae, but occur in certain members of both the Zygopetalum and Huntleya clades. Trichomes are unbranched, uniseriate and multicellular with rounded apices, or unbranched and unicellular, with tapering, pointed and flexuose apices. Hitherto, unicellular trichomes of this kind have been observed only for euglossophilous orchid taxa, and the adoption of a relatively limited range of pollination strategies by Zygopetalinae may have resulted in reduced investment in micromorphological labellar characters.
PMCID: PMC3177679  PMID: 21856635
Cryptarrhena; epidermis; homoplasy; Huntleya clade; labellum; Maxillariinae; papillae; trichomes; Warrea clade; Zygopetalum clade
7.  Comparative anatomy of the nectary spur in selected species of Aeridinae (Orchidaceae) 
Annals of Botany  2010;107(3):327-345.
Background and Aims
To date, the structure of the nectary spur of Aeridinae has not been studied in detail, and data relating to the nectaries of ornithophilous orchids remain scarce. The present paper compares the structural organization of the floral nectary in a range of Aeridinae species, including both entomophilous and ornithophilous taxa.
Nectary spurs of Ascocentrum ampullaceum (Roxb.) Schltr. var. aurantiacum Pradhan, A. curvifolium (Lindl.) Schltr., A. garayi Christenson, Papilionanthe vandarum (Rchb.f.) Garay, Schoenorchis gemmata (Lindl.) J.J. Sm., Sedirea japonica (Rchb.f.) Garay & H.R. Sweet and Stereochilus dalatensis (Guillaumin) Garay were examined by means of light microscopy, scanning electron microscopy and transmission electron microscopy.
Key Results and Conclusions
The diverse anatomy of the nectary is described for a range of Aeridinae species. All species of Ascocentrum investigated displayed features characteristic of ornithophilous taxa. They have weakly zygomorphic, scentless, red or orange flowers, display diurnal anthesis, possess cryptic anther caps and produce nectar that is secluded in a relatively massive nectary spur. Unicellular, secretory hairs line the lumen at the middle part of the spur. Generally, however, with the exception of Papilionanthe vandarum, the nectary spurs of all entomophilous species studied here (Schoenorchis gemmata, Sedirea japonica, Stereochilus dalatensis) lack secretory trichomes. Moreover, collenchymatous secretory tissue, present only in the nectary spur of Asiatic Ascocentrum species, closely resembles that found in nectaries of certain Neotropical species that are hummingbird-pollinated and assigned to subtribes Maxillariinae Benth., Laeliinae Benth. and Oncidiinae Benth. This similarity in anatomical organization of the nectary, regardless of geographical distribution and phylogeny, indicates convergence.
PMCID: PMC3043926  PMID: 21183455
Aeridinae; collenchyma; entomophily; floral anatomy; micromorphology; nectar; nectary spur; Orchidaceae; ornithophily; trichomes
8.  Comparative histology of floral elaiophores in the orchids Rudolfiella picta (Schltr.) Hoehne (Maxillariinae sensu lato) and Oncidium ornithorhynchum H.B.K. (Oncidiinae sensu lato) 
Annals of Botany  2009;104(2):221-234.
Background and Aims
Floral elaiophores, although widespread amongst orchids, have not previously been described for Maxillariinae sensu lato. Here, two claims that epithelial, floral elaiophores occur in the genus Rudolfiella Hoehne (Bifrenaria clade) are investigated. Presumed elaiophores were compared with those of Oncidiinae Benth. and the floral, resin-secreting tissues of Rhetinantha M.A. Blanco and Heterotaxis Lindl., both genera formerly assigned to Maxillaria Ruiz & Pav. (Maxillariinae sensu stricto).
Putative, floral elaiophore tissue of Rudolfiella picta (Schltr.) Hoehne and floral elaiophores of Oncidium ornithorhynchum H.B.K. were examined by means of light microscopy, histochemistry, scanning electron microscopy and transmission electron microscopy.
Key Results and Conclusions
Floral, epithelial elaiophores are present in Rudolfiella picta, indicating, for the first time, that oil secretion occurs amongst members of the Bifrenaria clade (Maxillariinae sensu lato). However, whereas the elaiophore of R. picta is borne upon the labellar callus, the elaiophores of O. ornithorhynchum occur on the lateral lobes of the labellum. In both species, the elaiophore comprises a single layer of palisade secretory cells and parenchymatous, subsecretory tissue. Cell wall cavities are absent from both and there is no evidence of cuticular distension in response to oil accumulation between the outer tangential wall and the overlying cuticle in R. picta. Distension of the cuticle, however, occurs in O. ornithorhynchum. Secretory cells of R. picta contain characteristic, spherical or oval plastids with abundant plastoglobuli and these more closely resemble plastids found in labellar, secretory cells of representatives of Rhetinantha (formerly Maxillaria acuminata Lindl. alliance) than elaiophore plastids of Oncidiinae. In Rhetinantha, such plastids are involved in the synthesis of resin-like material or wax. Despite these differences, the elaiophore anatomy of both R. picta (Bifrenaria clade) and O. ornithorhynchum (Oncidiinae) fundamentally resembles that of several representatives of Oncidiinae. These, in their possession of palisade secretory cells, in turn, resemble the floral elaiophores of certain members of Malpighiaceae, indicating that convergence has occurred here in response to similar pollination pressures.
PMCID: PMC2710904  PMID: 19447811
Bifrenaria clade; elaiophore; floral oil; Heterotaxis; Maxillariinae; Oncidiinae; Oncidium ornithorhynchum; Rhetinantha; Rudolfiella picta; secretion
9.  Labellar Micromorphology of Two Euglossine-pollinated Orchid Genera; Scuticaria Lindl. and Dichaea Lindl. 
Annals of Botany  2008;102(5):805-824.
Background and Aims
Until recently, there was no consensus regarding the phylogenetic relationships of the Neotropical orchid genera Scuticaria Lindl. and Dichaea Lindl. However, recent evidence derived from both gross morphological and molecular studies supports the inclusion of Scuticaria and Dichaea in sub-tribes Maxillariinae and Zygopetalinae, respectively. The present paper describes the labellar micromorphology of both genera and seeks to establish whether labellar characters support the assignment of Scuticaria and Dichaea to these sub-tribes.
The labella of four species of Scuticaria and 14 species of Dichaea were examined using light microscopy and scanning electron microscopy, and their micromorphology was compared with that of representative species of Maxillariinae sensu lato and Zygopetalinae (Huntleya clade).
Key Results and Conclusions
In most specimens of Scuticaria examined, the papillose labella bear uniseriate, multicellular, unbranched trichomes. However, in S. steelii (Lindl.) Lindl., branched hairs may also be present and some trichomes may fragment and form pseudopollen. Multicellular, leaf-like scales were also present in one species of Scuticaria. Similar, unbranched hairs are present in certain species of Maxillaria Ruiz & Pav. (Maxillariinae sensu stricto) and Chaubardia Rchb.f. (Huntleya clade). As yet, moniliform, pseudopollen-forming hairs have not been observed for Zygopetalinae, but their presence in Scuticaria steelii, Maxillaria and Heterotaxis Lindl. supports the placing of Scuticaria in Maxillariinae. As other genera are sampled, the presence of branched hairs, hitherto unknown for Maxillariinae sensu lato, may prove to be a useful character in taxonomy and phylogenetic studies. Euglossophily occurs in Dichaea, as well as Chondrorhyncha Lindl. and Pescatorea Rchb.f. (Huntleya clade), and all three genera tend to lack distinctive labellar features. Instead, lip micromorphology is relatively simple and glabrous or papillose. However, two of the Dichaea species examined bear unicellular, labellar trichomes very similar to those found in Bifrenaria Lindl. (pollinated by both euglossine bees and Bombus spp.), and this feature may have arisen by convergence in response to similar pollination pressures.
PMCID: PMC2712378  PMID: 18765439
Bifrenaria; Bifrenaria clade; Chaubardia; Chondrorhyncha; Dichaea; Dichaeinae; Heterotaxis; Huntleya clade; Huntleyinae; labellum; Maxillaria; Maxillariinae; papillae; Pescatorea; scales; Scuticaria; trichomes; Zygopetalinae
10.  Elaiophore Structure and Oil Secretion in Flowers of Oncidium trulliferum Lindl. and Ornithophora radicans (Rchb.f.) Garay & Pabst (Oncidiinae: Orchidaceae) 
Annals of Botany  2007;101(3):375-384.
Background and Aims
Many orchid flowers have glands called elaiophores and these reward pollinating insects with oil. In contrast to other reward-producing structures such as nectaries, the anatomy of the elaiophore and the process of oil secretion have not been extensively studied. In this paper, elaiophore structure is described for two members of Oncidiinae, Oncidium trulliferum Lindl. and Ornithophora radicans (Rchb.f.) Garay & Pabst.
Elaiophores of both species were examined using light microscopy, scanning electron microscopy and transmission electron microscopy.
Key Results and Conclusions
In flowers of Oncidium trulliferum and Ornithophora radicans, oil is secreted by morphologically distinct elaiophores associated with the labellar callus. However, in O. trulliferum, elaiophores also occur on the lateral lobes of the labellum. In both these species, the epithelial elaiophores are composed of a single layer of palisade-like epidermal cells and a distinct subepithelial layer. Secretory elaiophore cells may contain numerous, starchless plastids, mitochondria and smooth endoplasmic reticulum profiles. In O. trulliferum, the cytoplasm contains myelin-like figures but these are absent from O. radicans. In the former species, cavities occur in the cell wall and these presumably facilitate the passage of oil onto the elaiophore surface. In O. radicans, the accumulation of oil between the outer tangential wall and the cuticle causes the latter to become distended. Since it is probable that the full discharge of oil from the elaiophores of O. radicans occurs only when the cuticle is ruptured by a visiting insect, this may contribute towards pollinator specificity. The structure of the elaiophore in these species resembles both that found in previously investigated species of Oncidiinae and that of certain members of the Malpighiaceae.
PMCID: PMC2701824  PMID: 18056056
Elaiophore; Oncidium trulliferum; Ornithophora radicans; Orchidaceae; oil secretion; pollination
11.  Micromorphology of the Labellum and Floral Spur of Cryptocentrum Benth. and Sepalosaccus Schltr. (Maxillariinae: Orchidaceae) 
Annals of Botany  2007;100(4):797-805.
Background and Aims
Gross vegetative and floral morphology, as well as modern molecular techniques, indicate that Cryptocentrum Benth. and Sepalosaccus Schltr. are related to Maxillaria Ruiz & Pav. However, they differ from Maxillaria in their possession of floral spurs and, in this respect, are atypical of Maxillariinae. The labellar micromorphology of Maxillaria, unlike that of the other two genera, has been extensively studied. In the present report, the labellar micromorphology of Cryptocentrum and Sepalosaccus is compared with that of Maxillaria and, for the first time, the micromorphology of the floral spur as found in Maxillariinae is described.
Labella and dissected floral spurs of Cryptocentrum and Sepalosaccus were examined using light microscopy (LM) and scanning electron microscopy (SEM).
Key Results
In each case, the labellum consists of a papillose mid-lobe (epichile), a cymbiform region (hypochile) and, proximally, a spur, which is pronounced in Cryptocentrum but short and blunt in Sepalosaccus. The inner epidermal surface of the spur of Cryptocentrum is glabrous or pubescent, and the bicellular hairs, where present, are unlike any hitherto described for Maxillariinae. Similar but unicellular hairs also occur in the floral spur of Sepalosaccus, whereas the glabrous epidermis lining the spur of C. peruvianum contains putative nectar pores.
The labellar micromorphology of Cryptocentrum and Sepalosaccus generally resembles that of Maxillaria. The floral spur of Cryptocentrum displays two types of organization in that the epidermal lining may be glabrous (possibly with nectar pores) or pubescent. This may have taxonomic significance and perhaps reflects physiological differences relating to nectar secretion. The trichomes found within the spurs of Cryptocentrum and Sepalosaccus more closely resemble the hairs of certain unrelated, nectariferous orchid taxa than those found in the largely nectarless genus Maxillaria, and this further supports the case for parallelism.
PMCID: PMC2749631  PMID: 17686763
Labellum; Maxillariinae; micromorphology; nectar pore; nectary; spur; trichome

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