Comparative labellar micromorphology of Zygopetalinae (Orchidaceae)

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.

Methods

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.     

Comparative histology of floral elaiophores in the orchids Rudolfiella picta (Schltr.) Hoehne (Maxillariinae sensu lato) and Oncidium ornithorhynchum H.B.K. (Oncidiinae sensu lato)

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).

Methods

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.Key words: Bifrenaria clade, elaiophore, floral oil, Heterotaxis, Maxillariinae, Oncidiinae, Oncidium ornithorhynchum, Rhetinantha, Rudolfiella picta, secretion     

Labellar micromorphology of Bifrenariinae Dressler (Orchidaceae)

BACKGROUND AND AIMS: The two closely related subtribes Bifrenariinae Dressler and Maxillariinae Benth. are easily distinguished on morphological grounds. Recently, however, molecular techniques have supported the inclusion of Bifrenariinae within a more broadly defined Maxillariinae. The present paper describes the diverse labellar micromorphology found amongst representatives of Bifrenariinae (Bifrenaria Lindl., Rudolfiella Hoehne, Teuscheria Garay and Xylobium Lindl.) and compares it with that found in Maxillaria Pabst & Dungs and Mormolyca Fenzl (Maxillariinae). METHODS: The labella of 35 specimens representing 22 species of Bifrenariinae were examined by means of light microscopy and scanning electron microscopy and their micromorphology compared with that of Maxillaria sensu stricto and Mormolyca spp. The labellar epidermis of representatives of Bifrenaria, Xylobium and Mormolyca was tested for protein, starch and lipids in order to ascertain whether this tissue is involved in the rewarding of pollinators. KEY RESULTS AND CONCLUSIONS: The labella of Bifrenaria spp. and Mormolyca spp. are densely pubescent but those of Xylobium, Teuscheria and Rudolfiella are generally papillose. However, whereas the trichomes of Bifrenaria and Mormolyca are unicellular, those found in the other three genera are multicellular. Hitherto, no unicellular trichomes have been described for Maxillaria, although the labella of a number of species secrete a viscid substance or bear moniliform, pseudopollen-producing hairs. Moniliform hairs and secretory material also occur in certain species of Xylobium and Teuscheria and these genera, together with Maxillaria, are thought to be pollinated by stingless bees (Meliponini). Differences in the labellar micromorphology of Bifrenaria and Mormolyca are perhaps related to Euglossine- and/ or bumble bee-mediated pollination and pseudocopulation, respectively. Although Xylobium and Teuscheria share a number of labellar features with Maxillaria sensu stricto, this does not necessarily reflect taxonomic relationships but may be indicative of convergence in response to similar pollinator pressures.     

Micromorphology of the labellum and floral spur of Cryptocentrum Benth. and Sepalosaccus Schltr. (Maxillariinae: Orchidaceae)

Background and Aims: Gross vegetative and floral morphology, as well as modern moleculartechniques, indicate that Cryptocentrum Benth. and SepalosaccusSchltr. are related to Maxillaria Ruiz & Pav. However, theydiffer from Maxillaria in their possession of floral spurs and,in this respect, are atypical of Maxillariinae. The labellarmicromorphology of Maxillaria, unlike that of the other twogenera, has been extensively studied. In the present report,the labellar micromorphology of Cryptocentrum and Sepalosaccusis compared with that of Maxillaria and, for the first time,the micromorphology of the floral spur as found in Maxillariinaeis described. Methods: Labella and dissected floral spurs of Cryptocentrum and Sepalosaccuswere examined using light microscopy (LM) and scanning electronmicroscopy (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 bluntin Sepalosaccus. The inner epidermal surface of the spur ofCryptocentrum 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 spurof Sepalosaccus, whereas the glabrous epidermis lining the spurof C. peruvianum contains putative nectar pores. Conclusions: The labellar micromorphology of Cryptocentrum and Sepalosaccusgenerally resembles that of Maxillaria. The floral spur of Cryptocentrumdisplays two types of organization in that the epidermal liningmay be glabrous (possibly with nectar pores) or pubescent. Thismay have taxonomic significance and perhaps reflects physiologicaldifferences relating to nectar secretion. The trichomes foundwithin the spurs of Cryptocentrum and Sepalosaccus more closelyresemble the hairs of certain unrelated, nectariferous orchidtaxa than those found in the largely nectarless genus Maxillaria,and this further supports the case for parallelism.     

Structure and distribution of floral trichomes in Lycaste and Sudamerlycaste (Orchidaceae: Maxillariinae s.l.)

Phylogenetic analysis indicates that Lycastinae should be incorporated into a more broadly defined Maxillariinae. This is supported by several anatomical features, including the presence of sunken, glandular trichomes in both Lycastinae and Maxillariinae s.s. Until recently, these were known only from vegetative organs, but have since been reported from flowers of Maxillaria dichroma. One character currently used to distinguish between Lycaste and Sudamerlycaste is the distribution of floral trichomes. In this article, we test the reliability of this character, describe the floral micromorphology of Lycaste and Sudamerlycaste and investigate whether their flowers bear sunken hairs. Their floral micromorphology is compared with that of other genera currently assigned to Maxillariinae s.l. Flowers of Lycaste and Sudamerlycaste bear conical or obpyriform papillae and unbranched and unequally branched multicellular trichomes. Contrary to previous reports that trichomes are confined to the column in Sudamerlycaste, they also occur in the tepal axils. Labellar trichomes, although often present in Lycaste, are lacking in Sudamerlycaste. In Lycaste sections Lycaste and Aromaticae, floral trichomes tend to be unbranched, whereas section Intermediae has both unbranched and branched hairs. Branched hairs are more common in Sudamerlycaste. Some hairs are tracheoidal, pitted and lignified. These mainly occur in section Lycaste and, to a degree, in section Intermediae, but are absent from section Aromaticae and most species of Sudamerlycaste. Branched column hairs, present in Sudamerlycaste, are absent from all sections of Lycaste, and tracheoidal column hairs occur only in Sudamerlycaste. Sunken floral hairs are absent from both genera. Trichome structure and distribution may prove useful in distinguishing between these taxa and in elucidating the intergeneric relationships of Maxillariinae s.l.© 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 409–421.     

Molecular phylogenetics and the evolution of fruit and leaf morphology of Dichaea (Orchidaceae: Zygopetalinae)

Background and Aims

The orchid genus Dichaea, with over 100 species found throughout the neotropics, is easily recognized by distichous leaves on long stems without pseudobulbs and flowers with infrastigmatic ligules. The genus has previously been divided into four sections based primarily on presence of ovary bristles and a foliar abscission layer. The aim of this work is to use DNA sequence data to estimate phylogenetic relationships within Dichaea and map the distribution of major morphological characters that have been used to delimit subgenera/sections.

Methods

Sequence data for the nuclear ribosomal internal transcribed spacers and plastid matK, trnL intron, trnL-F spacer and ycf1 for 67 ingroup and seven outgroup operational taxonomic units were used to estimate phylogenetic relationships within Dichaea. Taxa from each of the four sections were sampled, with the greatest representation from section Dichaea, the most diverse and taxonomically puzzling group.

Key Results

Molecular data and morphology support monophyly of Dichaea. Results indicate that section Dichaeopsis is polyphyletic and based on symplesiomorphies, including deciduous leaves and smooth ovaries that are widespread in Zygopetalinae. There are at least three well-supported clades within section Dichaeopsis. Section Pseudodichaea is monophyletic and defined by setose ovaries and leaves with an abscission layer. Sections Dichaea and Dichaeastrum are monophyletic and defined by pendent habit and persistent leaves. Section Dichaeastrum, distinguished from section Dichaea primarily by a glabrous ovary, is potentially polyphyletic.

Conclusions

The leaf abscission layer was lost once, occurring only in the derived sections Dichaea and Dichaeastrum. The setose fruit is a more homoplasious character with several losses and gains within the genus. We propose an informal division of the genus based upon five well-supported clades.Key words: Dichaea, matK, nrITS, Orchidaceae, trnL intron, trnL-F spacer, ycf1, Zygopetalinae     

Comparative anatomy of the nectary spur in selected species of Aeridinae (Orchidaceae)

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.

Methods

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.     

Molecular phylogeny of the neotropical genus Christensonella (Orchidaceae, Maxillariinae): species delimitation and insights into chromosome evolution

Background and Aims

Species'' boundaries applied within Christensonella have varied due to the continuous pattern of variation and mosaic distribution of diagnostic characters. The main goals of this study were to revise the species'' delimitation and propose a more stable classification for this genus. In order to achieve these aims phylogenetic relationships were inferred using DNA sequence data and cytological diversity within Christensonella was examined based on chromosome counts and heterochromatin patterns. The results presented describe sets of diagnostic morphological characters that can be used for species'' identification.

Methods

Phylogenetic studies were based on sequence data of nuclear and plastid regions, analysed using maximum parsimony and maximum likelihood criteria. Cytogenetic observations of mitotic cells were conducted using CMA and DAPI fluorochromes.

Key Results

Six of 21 currently accepted species were recovered. The results also support recognition of the ‘C. pumila’ clade as a single species. Molecular phylogenetic relationships within the ‘C. acicularis–C. madida’ and ‘C. ferdinandiana–C. neowiedii’ species'' complexes were not resolved and require further study. Deeper relationships were incongruent between plastid and nuclear trees, but with no strong bootstrap support for either, except for the position of C. vernicosa. Cytogenetic data indicated chromosome numbers of 2n = 36, 38 and 76, and with substantial variation in the presence and location of CMA/DAPI heterochromatin bands.

Conclusions

The recognition of ten species of Christensonella is proposed according to the molecular and cytogenetic patterns observed. In addition, diagnostic morphological characters are presented for each recognized species. Banding patterns and chromosome counts suggest the occurrence of centric fusion/fission events, especially for C. ferdinandiana. The results suggest that 2n = 36 karyotypes evolved from 2n = 38 through descendent dysploidy. Patterns of heterochromatin distribution and other karyotypic data proved to be a valuable source of information to understand evolutionary patterns within Maxillariinae orchids.Key words: Chromosome number, Christensonella, Cymbidieae, cytotaxonomy, fluorochrome staining, Maxillaria, Maxillariinae, molecular phylogenetics, species delimitation     

Nectar and oleiferous trichomes as floral attractants in <Emphasis Type="Italic">Bulbophyllum saltatorium</Emphasis> Lindl. (Orchidaceae)

Although many Orchidaceae have deceit flowers that produce no reward, the most common reward, when present, is nectar. Bulbophyllum, however, is unusual in that the labellar secretions of most species investigated to date lack sugars, and, therefore, cannot be considered true nectar. The African species Bulbophyllum saltatorium is an exception in that it produces not only nectar but also possesses specialized, capitate oleiferous trichomes. The nectary of B. saltatorium is borne on the labellum and is represented by a deep, narrow, median longitudinal groove, having a small aperture, and flanked by trichomes. Isodiametric epidermal cells lining this groove secrete nectar which collects both in the groove and on the surface of the labellum. As well as a nectary, the labellum of B. saltatorium also bears three types of unicellular trichomes: the longest trichomes are borne distally and abaxially; the marginal ones form a rim around the entire labellum, and finally, massive, capitate trichomes occur proximally and adaxially. These are oleiferous, containing large quantities of oil which might function as precursors of volatile components of fragrance or provide a food-reward. To the best of our knowledge, this is the first time for such oleiferous trichomes to be described for Bulbophyllum. Therefore, apart from their color and markings, flowers of this species are able to attract pollinators in at least two, possibly three ways: food-reward in the form of nectar; fragrance; and possibly food-rewards in the form of food-hairs.     

Ultrastructure of the labellar epidermis in selected Maxillaria species (Orchidaceae)

The ultrastructure of the labellar epidermis of 13 species of Maxillaria and one hybrid was examined using low-vacuum scanning electron microscopy (SEM). The labellum may be homogeneous and glabrous or papillose, comprising one type of cell only, or heterogeneous with papillae, uniseriate trichomes and/or glands in various combinations. The trichomes are unbranched and multicellular with pointed or truncated tips. Moreover, in some taxa, moniliform trichomes occur, and these are thought to fragment with the formation of pseudopollen. Homogeneous and heterogeneous labellar organization may represent separate evolutionary lines. Preliminary results suggest that labellar features may provide additional taxonomic characters allowing determination of intrageneric affinities.     

Pseudopollen in Eria Lindl. section Mycaranthes Rchb.f. (Orchidaceae)

BACKGROUND AND AIMS: Pseudopollen is a whitish, mealy material produced upon the labella of a number of orchid species as labellar hairs either become detached or fragment. Since individual hair cells are rich in protein and starch, it has long been speculated that pseudopollen functions as a reward for visiting insects. Although some 90 years have passed since Beck first described pseudopollen for a small number of Eria spp. currently assigned to section Mycaranthes Rchb.f., we still know little about the character of pseudopollen in this taxon. The use of SEM and histochemistry would re-address this deficit in our knowledge whereas comparison of pseudopollen in Eria (S.E. Asia), Maxillaria (tropical and sub-tropical America), Polystachya (largely tropical Africa and Madagascar) and Dendrobium unicum (Thailand and Laos) would perhaps help us to understand better how this feature may have arisen and evolved on a number of different continents. METHODS: Pseudopollen morphology is described using light microscopy and scanning electron microscopy. Hairs were tested for starch, lipid and protein using IKI, Sudan III and the xanthoproteic test, respectively. KEY RESULTS AND CONCLUSIONS: The labellar hairs of all eight representatives of section Mycaranthes examined are identical. They are unicellular, clavate with a narrow 'stalk' and contain both protein and starch but no detectable lipid droplets. The protein is distributed throughout the cytoplasm and the starch is confined to amyloplasts. The hairs become detached from the labellar surface and bear raised cuticular ridges and flaky deposits that are presumed to be wax. In that they are unicellular and appear to bear wax distally, the labellar hairs are significantly different from those observed for other orchid species. Comparative morphology indicates that they evolved independently in response to pollinator pressures similar to those experienced by other unrelated pseudopollen-forming orchids on other continents.     

Gustatory mechanisms and sugar-feeding in the mosquito, Culiseta inornata

ABSTRACT. Gustatory hairs on the legs and mouthparts of the mosquito, Culiseta inornata , were stimulated with sucrose solutions to determine their role in the finding and consuming of nectar by females. Stimulation of tarsi initiated probing, which continued without subsequent stimulation of tarsal hairs. Turning in response to tarsal stimulation depended on which leg was stimulated. Once gustatory hairs on the labella were stimulated, turning and probing were discontinued. Stimulation of the hairs on the external surface of the labella apparently initiates the labellar opening response, while stimulation of hairs on the oral surface of the labella maintains the labellar response. Electrophysiologically recorded activity of cibarial and pharyngeal pumps was used to assess the influence of the five relevant sets of gustatory hairs on initiation of sucking. None of the sets alone were capable of initiating sucking. Sucking was initiated when the hairs on the oral surface of the labella were stimulated simultaneously with sensory hairs on the tip of the labrum. The gustatory hairs on the oral surface of the labella exerted considerable influence in determining the amount of sugar or water imbibed.     

Atypical pseudopollen-forming hairs in Maxillaria (Orchidaceae)

Pseudopollen is found on the labella of several species of Maxillaria and is formed by the fragmentation of uniseriate, multicellular, moniliform trichomes. The resultant component cells are rich in protein. Since flowers of pseudopollen-forming species generally lack nectar, it is probable that pseudopollen gradually replaced nectar as the pollinator reward. However, direct evidence for this hypothesis is lacking. The present paper examines the labellar micromorphology of five Brazilian species of Maxillaria assigned to the M. discolor alliance. The flowers of two of these species, namely M. violaceopunctata and M. villosa , produce both food hairs and a lipoidal, labellar secretion which is rich in aromatic amino acids. Moreover, in the case of M. violaceopunctata , the secretion was found to contain reducing sugars. This may represent an intermediate stage in the transition from nectar-producing to pseudopollen-forming flowers. SEM studies indicate how pseudopollen-forming, moniliform trichomes, such as those found in the Maxillaria grandiflora complex, may have evolved from simple, uniseriate, multicellular hairs.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 143 , 151−158.     

Insight into the structure and chemistry of glandular trichomes of Labiatae, with emphasis on subfamily Lamioideae

Glandular trichomes of Labiatae are among the most investigated secretory structures. Most species studied belong to subfamily Nepetoidae, including plants with aromatic properties, while so far a few species of subfamily Lamioideae were examined. In this work, we studied the micromorphology, ultrastructure, type and release of secretion of the glandular trichomes present on leaves and flowers of several species belonging to subfamily Lamioideae, (Stachys alopecuros (L.) Bentham subsp. alopecuros, S. officinalis (L.) Trevisan subsp. officinalis, S. germanica L. subsp. germanica, S. germanica L. subsp. salviifolia (Ten.) Gams, S. sylvatica L., S. heraclea All., S. plumosa Griseb., S. annua L., Prasium majus L., Sideritis romana L.) and one to the sister group Scutellarioideae (Scutellaria galericulata L.). Besides the well-known peltate and small capitate trichomes, widely described in the literature, other types of glandular trichomes were encountered; stalked peltate hairs and large capitate hairs. In particular, a new type of capitate trichome, exclusive of calices and corollas, which presents a mode and release of secretion never described before, is reported.     

Pseudopollen in Dendrobium unicum Seidenf. (Orchidaceae): Reward or Deception?

BACKGROUND AND AIMS: In 1987, Kjellsson and Rasmussen described the labellar trichomes of Dendrobium unicum Seidenf. and proposed that these hairs function as pseudopollen. Pseudopollen is a mealy material that superficially resembles pollen, is usually laden with food substances and is formed when labellar hairs either fragment into individual cells or become detached from the labellum. However, the trichomes of D. unicum are very different from pseudopollen-forming hairs found in other orchid genera such as Maxillaria and Polystachya. Moreover, Kjellsson and Rasmussen were unable to demonstrate the presence of food substances within these trichomes and argued that even in the absence of food substances, the hairs, in that they superficially resemble pollen, can still attract insects by deceit. The aim of this paper is to investigate whether the labellar trichomes of D. unicum contain food reserves and thus reward potential pollinators or whether they are devoid of foods and attract insects solely by mimicry. METHODS: Light microscopy, histochemistry and transmission electron microscopy. KEY RESULTS: Dendrobium unicum produces pseudopollen. Pseudopollen here, however, differs from that previously described for other orchid genera in that the pseudopollen-forming trichomes consist of a stalk cell and a 'head' of component cells that separate at maturity, in contrast to Maxillaria and some Polystachya spp. where pseudopollen is formed by the fragmentation of moniliform hairs. Moreover, the pseudopollen of Maxillaria and Polystachya largely contains protein, whereas in D. unicum the main food substance is starch. CONCLUSIONS: Flowers of D. unicum, rather than attracting insects solely by deceit may also reward potential pollinators.     

Comparative labellum micromorphology of the sexually deceptive temperate orchid genus Ophrys: diverse epidermal cell types and multiple origins of structural colour

Labellum micromorphology was imaged via scanning electron and light microscopy in 32 microspecies and one artificial hybrid of the European terrestrial orchid genus Ophrys, together representing all ten macrospecies circumscribed in the genus via molecular phylogenetics. Imaging of homologous regions of the adaxial surface, paying particular attention to the diagnostic feature of the comparatively reflective speculum, revealed the presence of between three and seven epidermal cell types on each labellum, the less complex labella being plesiomorphic. Epidermal protuberances range from short, domed papillae to long, twisted unicellular filaments. Multiple origins are inferred for pale labellar margins, large yellow appendices (both putative osmophores exuding pseudopheromones), broad flat labella and long lateral horns. Homoplasy in the speculum is manifested in unusually complex or simple outlines and the presence or absence of a pale margin or iridescence. The reflectivity of the speculum is caused by a combination of chemical and physical colour, whereas iridescence can be caused only by physical properties. The specula of most microspecies studied bear striated trichomes, albeit maturing comparatively late in ontogeny and being sufficiently narrow to allow light to reach the flat polygonal trichome bases. Reflectivity appears to be negatively correlated with the convexity and degree of cuticular corrugation shown by these epidermal cells. Two clades (the Speculum + Tenthredinifera + Bombyliflora group and Bertolonii subgroup of the Sphegodes group) have lost specular trichomes and include the most iridescent species; their flat, polygonal, nonstriated cells resemble those observed on the paired pseudoeyes that bracket the stigmas of all Ophrys except the Fusca group. The smooth thick‐layered cuticle and dense layers of organelles and starch bodies revealed by preliminary transmission electron microscopy study provide alternative candidates for the primary reflective surface of the speculum; in contrast, the trichomes and conical cells that dominate Ophrys labella, and occur on the specula of all but the most reflective species, absorb and/or diffuse light. Multiple MYB family genes are hypothesized to control epidermal micromorphology. The relative contributions of olfactory, visual and tactile cues to the sophisticated pseudocopulatory pollination mechanism that characterizes Ophrys remain unclear, but the degree of reproductive isolation achieved, and thus the speciation rate, have certainly been greatly exaggerated by most observers. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 504–540.     

Trichome morphology provides phylogenetically informative characters for Tremandra, Platytheca and Tetratheca (former Tremandraceae)

Summary Trichomes of Tremandra R.Br. ex DC., Platytheca Steetz and Tetratheca Sm. (Elaeocarpaceae, former Tremandraceae), together with two outgroup species of Elaeocarpus L., are illustrated using scanning electron microscopy, and their distribution on various plant organs is documented. Various trichomes types were identified that relate taxa: simple hairs, stellate hairs, short glandular trichomes, long glandular trichomes, and three forms of tubercules. Both outgroup and ingroup taxa have simple hairs. Stellate hairs are confirmed as unique to Tremandra. Prominent and sculptured multicelled tubercules, some bearing a stout hair, are characteristic of Platytheca. Smaller multicelled tubercules occur in both Platytheca and Tetratheca, except for the Western Australian taxon Te. filiformis Benth. (possibly plesiomorphic). Unicellular tubercules (papilla) characterise two species of Tetratheca. Short glandular trichomes, usually found on the ovary, also occur in both of these genera but not in all species (possibly secondary losses), while long glandular trichomes, usually on stems and leaves, occur only in some groups of Tetratheca. Within Tetratheca, Western Australian taxa that have five-merous flowers fall into three ‘groups’: seven species (together with one from South Australia) that have short glandular trichomes but no long glandular trichomes; six species that have long glandular trichomes but no short glandular trichomes; and four species that have both trichome types. All other species of Tetratheca have four-merous flowers and form two ‘groups’: 12 eastern species (including one from South Australia) that have both short glandular trichomes and long glandular trichomes; 4 western species and six eastern species that lack short glandular trichomes. On the basis of these characters, a phylogenetic hypothesis for the three genera is presented.     

Floral elaiophores in Lockhartia Hook. (Orchidaceae: Oncidiinae): their distribution,diversity and anatomy

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.

Methods

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.