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.     

Ontogeny and phylogeny of Brownleea (Orchidoideae: Orchidaceae)

The phylogeny of the African orchidoid genus Brownleea was investigated, using morphological characters. It has been suggested that the genus may be of hybrid origin, a hypothesis supported by the presence of two very different types of stigma ontogenies. Morphological investigations of all the species revealed that two species have stigmas derived from all three carpel apices, the 'normal' situation in the Orchidaceae. The remaining five species have stigmas derived from only the median carpel, a very unusual situation found in the Coryciinae. A phylogenetic analysis of all available morphological data for all species supports the monophyly of the genus. based on several distinct synapomorphies. The variation in stigma ontogeny may be due either to parallelism, or to an earlier hybridization event. The analysis supported the recognition of several distinct groupings within Brownleea . Two of these groupings are supported irrespective of which putative parent is used as sister-group to the genus, while a third grouping is dependent on the use of the as sister-group.     

Comparative vegetative anatomy and classification of Diseae (Orchidaceae)

The leaf, stem, root, tuber and dropper anatomy of the orchid tribe Diseae (including the subtribes Satyriinae, Disinae, Brownlecinac, Huttonaeinae and Coryciinae) is reviewed. The study is largely based on investigations of 123 species, and data from several previous publications have also been incorporated. Two characters were identified as being taxonomically valuable: (1) the presence of sclerenchyma caps associated with leaf vascular bundles, and (2) the degree of dissection of the siphonostele of the tuber ('polystelic' or 'monostelic'). The phylogenetic analysis shows that anatomical characters do not change the basic structure of a cladogram that is based on morphological characters. The taxa of Diseae are discussed on the basis of anatomical data. Subtribes Satyriinae (excluding the anatomically unusual genus Pachites), Brownleeinae, Huttonaeinae, and Coryciinae are uniform in. critical anatomical characters. However, subtribe Disinae is rather diverse in vegetative anatomy. Disa sect. Micranthae differs from the rest of the genus in its leaf anatomy. The occurrence of foliar sclerenchyma bundle caps and 'polystelic' tubers supports the incorporation of Herschelianthe in Disa sect. Stenocarpa.     

Comparative vegetative anatomy and classification of Diseae (Orchidaceae)

The leaf, stem, root, tuber and dropper anatomy of the orchid tribe Diseae (including the subtribes Satyriinae, Disinae, Brownlecinac, Huttonaeinae and Coryciinae) is reviewed. The study is largely based on investigations of 123 species, and data from several previous publications have also been incorporated. Two characters were identified as being taxonomically valuable: (1) the presence of sclerenchyma caps associated with leaf vascular bundles, and (2) the degree of dissection of the siphonostele of the tuber (‘polystelic’ or ‘monostelic’). The phylogenetic analysis shows that anatomical characters do not change the basic structure of a cladogram that is based on morphological characters. The taxa of Diseae are discussed on the basis of anatomical data. Subtribes Satyriinae (excluding the anatomically unusual genus Pachites), Brownleeinae, Huttonaeinae, and Coryciinae are uniform in. critical anatomical characters. However, subtribe Disinae is rather diverse in vegetative anatomy. Disa sect. Micranthae differs from the rest of the genus in its leaf anatomy. The occurrence of foliar sclerenchyma bundle caps and ‘polystelic’ tubers supports the incorporation of Herschelianthe in Disa sect. Stenocarpa.     

Comparative vegetative anatomy and systematics of Spiranthoideae (Orchidaceae)

STERN, W. L., MORRIS, M. W., JUDD, W. S., PRIDGEON, A. M. & DRESSLER, R. L. 1993. Comparative vegetative anatomy and systematics of Spiranthoideae (Orchidaceae). The anatomy of leaf, stem and root of plants in the orchid subfamily Spiranthoideae was studied and described from the viewpoint of systematics. Plants were available from most of the geographic range. Tribes Diceratosteleae and Tropidieae show sinuous anticlinal epidermal cell walls in leaves, glandular foliar hairs, tetracytic para-mesoperigenous stomata, unitary tracheary components in the foliar midrib, foliar and cauline stegmata and sclerenchyma, typical cruciate starch grains, thick-walled exodermal, endodermal, and pericyclic cells, and conductive strands of the root embedded in sclerenchyma. The tribe Cranichideae shows straight to curvilinear anticlinal epidermal cell walls in leaves, lack glandular foliar hairs, have variably patterned mesoperigenous stomata, lack sclerenchyma throughout the parts studied, have a binary tracheary component in the foliar midrib, store starch in specialized amyloplasts (spiranthosomes), lack stegmata, have thin-walled exodermal, endodermal, and pericyclic cells, show scalariform thickenings in exodermal cells, and have conductive strands of the root embedded in parenchyma. In Cryptostylis the tracheary component of the foliar midrib is unitary, stomata lack subsidiary cells, starch grains are of the typical cruciate configuration, and passage cells of the endodermis are apparently associated with tilosomes. Anatomical data, when analysed cladistically, support the hypothesis that Spiranthoideae, as currently delimited, are polyphyletic. Corymborkis, Tropidia, and Diceratostele are more closely related to Palmorchis, a likely representative of a basal clade within subfamily Epidendroideae, than to genera of Cranichideae. Likewise, members of Cranichideae are more closely related to Diuris, a representative of subfamily Orchidoideae-tribe Diurideae, than to Corymborkis, Tropidia and Diceratostele. The Corymborkis– Tropidia-Diceratostele-bassd epidendroid [Palmorchis) clade may be diagnosed by the foliar synapomorphies of sinuous anticlinal walls of epidermal cells and presence of glandular hairs. The Cranichideae-orchidoid (Diuris) clade may be diagnosed by its variably patterned, mesoperigenous stomata, lack of vascular bundle sclerenchyma, absence of stegmata, unthickened endodermal cell walls in roots, and conductive cells of roots embedded in parenchyma. Relationships within this clade are quite unresolved, when only anatomical data are employed; however, all studied genera of Cranichideae, except Cryptostylis, possess a binary tracheary component in the foliar midrib. Cranichideae, excluding Cryptostylis, may be considered monophyletic. All Cranichideae, except Helaeria and Cryptostylis, possess spiranthosomes. Hetaeria may be a basal member within Cranichideae. We consider the phylogenetic position of Cryptostylis, in relation to Cranichideae vs. Diurideae, to be equivocal.     

Gynostemium structure and relationships of theCorallorhizinae (Orchidaceae: Epidendroideae)

Several types of pollinium stalk are present in theCorallorhizinae. Govenia has a cellular epidermal pollinium stalk, whileTipularia has a unique stipe that results from prolongation and detachment of the rostellum.Dactylostalix andEphippianthus have no stipe, but do have a detachable viscidium.Aplectrum, Corallorhiza, Cremastra, andOreorchis have hamuli. Cladistic analysis of morphological characters suggests that these four genera form a coreCorallorhizinae, and are sister group to a clade includingTipularia, Calypso, andYoania (the latter two possessing a true tegula).Govenia is shown to be most closely related to cymbidioid genera (such asEulophia), sharing with them the cellular epidermal pollinium stalk andCymbidium type velamen, and indicating that removal ofGovenia fromCorallorhizinae is appropriate.Dactylostalix andEphippianthus appear to occupy a more basal position in the subfamily, further arguing that the subtribe as previously recognized is paraphyletic.     

Exine micromorphology and ultrastructure in Neottieae (Epidendroideae,Orchidaceae)

The diverse epidendroid orchid tribe Neottieae is characterized by multiple transitions between autotrophy and mycoheterotrophy, allogamous and autogamous mating systems, pollen released as tetrads or monads, and pollen exine tectate or semitectate. We use transmission and scanning electron microscopy on pollen of ten species of Neottieae to investigate whether the differences in pollen aggregation and exine micromorphology and ultrastructure reflect phylogenetic relationships, or whether this variation is subject to ecological constraints. Our results showed that differences in exine micromorphology are mostly concordant with phylogenetic relationships in Neottieae, i.e. an ascending tendency of pollen ornamentation from tectate (Cephalanthera) to semitectate (e.g. Neottia). In contrast, pollen aggregation, when plotted on the most recent phylogeny, shows repeated transitions between monads and tetrads that could be related to ecological constraints. Tetrads are present in species that are nectar rewarding, whereas monads are common in deceptive species. Cephalanthera is characterized by recalcitrant pollen, including the frequent occurrence of collapsed pollen. In this genus, the observed shifts from allogamous to autogamous or cleistogamous mating systems could help to reduce pollen damage caused by exposure to dry habitats.     

A new species of Scaphyglottis (Orchidaceae,Epidendroideae) from Colombia

A new species of Scaphyglottis from Colombia is described, illustrated and placed within the key for the determination of national Scaphyglottis species. Its taxonomic affinity is briefly discussed and the information about its distribution and ecology are provided.     

Comparative anatomy and systematics of Senghas's cushion species of Maxillaria (Orchidaceae)

Using data obtained through anatomy and morphology, we used cladistics to examine the monophyly of Senghas's proposed classification of Maxillaria cushion plants and his placement of Mormolyca ringens. Trignidium obtusum was chosen as the outgroup. Leaves have multicellular hairs sunken in crypts, primarily anomocytic or primarily tetracytic stomatal apparatuses, homogeneous mesophyll, and scattered fibre bundles. Three types of adaxial hypodermis were observed: (1) water-storage cells, (2) fibre bundles scattered among water-storage cells, and (3) fibre bundles scattered among chlorenchymatous cells. Abaxial hypodermis of fibre bundles occurs in several Maxillaria species and in Trigonidium obtusum. At the midvein of the leaf, adaxial mesophyll cells of most species are anticlinally extended and empty, and the abaxial mesophyll is usually collenchymatous. Vascular bundles are collateral and usually in a single series. Pseudobulb epidermal cell walls are thin, or outer walls are thickened. Ground tissue consists of water-storage and assimilatory cells with vascular bundles and associated lacunae scattered throughout. Roots are velamentous and exodermal cell walls are usually n-thickened with tenuous bands of scalarifom thickenings on longitudinal walls. Tilosomes may be plaited, baculate, or spongy. Endodermal cell walls are usually U-thickened and pericycle cell walls are usually O-thickened opposite phloem sectors. Stegmata line the periphery of the thickened pericycle cells opposite phloem sectors in M. picta. Pith may be parenchymatous or sclerenchymatous. According to our phylogenetic analysis, Mormolyca ringens is consistently nested within the cladistic structure of Maxillaria. Therefore, Maxillaria likely is paraphyletic if Mormolyca ringens is recognized as generically distinct. It appears that Senghas's subgroup divisions of the unifoliate pseudobulbous maxillarias may also be artificial.     

Phylogeny of subfamily Epidendroideae (Orchidaceae) inferred from ndhF chloroplast gene sequences

This project undertakes the first molecular-based phylogenetic study of subfamily Epidendroideae (Orchidaceae). Approximately 1200 nucleotides (from the 3' half of the chloroplast gene ndhF for 34 orchid taxa and a lilioid monocot, Clivia miniata (Amaryllidaceae), were subjected to phylogenetic analysis using parsimony and maximum likelihood methods. Oryza sativa (Poaceae), a nonlilioid monocot, was designated as outgroup. Trees from both parsimony and maximum likelihood methods suggest that subfamily Epidendroideae is monophyletic, with Listera (Neottieae) as sister. Although subtribal relationships are typically well resolved and have strong branch support, intertribal relationships are generally poorly resolved. Perhaps this general lack of resolution among tribes reflects a rapid species radiation that coincided with anatomical, physiological, and anatomical adaptations that initiated large-scale epiphytism in the ancestral Epidendroideae. Six taxa in this study exhibit deletions that are not evenly divisible by three and result in extensive sequence frameshifts. For example, one deletion is 227 bp in length and is flanked by the short direct repeat sequence; TCAATAGGAATTTCTTTT. Multiple deletions and frameshifts suggest that ndhF may be a pseudogene, in at least some orchid taxa.     

Fragrance analyses,an aid to taxonomic relationships of the genusCoryanthes (Orchidaceae)

All members of the investigated genusCoryanthes (subtribeStanhopeinae) are pollinated by male euglossine bees. The different fragrance profiles are the primary reproductive isolating mechanisms, because the flowers are interfertile. The fragrance patterns of 17 species ofCoryanthes were analyzed by gas chromatography as a means to improve the classification of this genus. A first amine (2-N-methylaminobenzaldehyde) was found to be the main fragrance compound of an as yet unclassifiedCoryanthes species.     

The stigma of Cephalanthera (Orchidaceae) provides a link between primitive and derived Epidendroideae

Micromorphological, anatomical and ultrastructural observations of the stigma of several Neottieae ( Cephalanthera damasonium, Epipactis palustris, Neottia nidusavis, Listera ovata ) and a derived epidendroid orchid ( Phaius tankervilliae ) were made. Among these taxa Cephalanthera is the only neottioid orchid possessing a WDc stigma type being typical for the derived Epidendroideae. Further features are a concave, non papillate stigma covered by a specialised cuticle, the arrangement of the anatomical zones, detached cells with conspicuous wall thickenings and the location of lipidic droplets and electron dense material in the stigmatic mucilage. It is suggested that Cephalanthera is more closely related to the derived Epidendroideae than any other neottioid orchid and thereby is a sister group to the derived Epidendroideae.     

Comparative petiole anatomy as an aid to the classification of the African genus Baphia Lodd. (Leguminosae–Papilionoideae– Sophoreae)

The petiole anatomy of 79 specimens representing 64 species of Baphia has been examined. Anatomical characters of the petiole provide supporting evidence to be used in the infra-generic classification of the genus. They correspond to systematic groupings identified on other criteria, such as comparative morphology, palynology and phytogeography.     

Leave it to the leaves: a molecular phylogenetic study of Malaxideae (Epidendroideae, Orchidaceae)

Nuclear ITS and plastid matK sequences were collected for 71 taxa of Malaxideae (Orchidaceae). Resulting cladograms are highly resolved and well supported by jackknife analyses. These indicate that the traditional classification system of the tribe using characters primarily related to floral morphology does not reflect the evolutionary history of these taxa. Rather, the tribe is split into two major clades: one of terrestrial species and another of epiphytes. Within the epiphytic clade, taxa with laterally compressed leaves (Oberonia) are monophyletic, whereas the remaining taxa (Liparis pro parte) have elongate conduplicate leaves and form a paraphyletic grade of at least two additional monophyletic lineages. Within the terrestrial clade, taxa with plicate leaves (Liparis p.p. and Malaxis p.p.) clearly separate from taxa with conduplicate leaves (Liparis p.p. and Malaxis p.p.). Although further taxon sampling should take place before nomenclature is changed, it seems evident that Malaxideae will need to be divided into at least seven genera. Furthermore, the transition from epiphytic to terrestrial habit is documented to have occurred only once in Malaxideae, and the value of vegetative over reproductive features in classifying some groups of orchids is again demonstrated.     

Vegetative anatomy of subtribe Habenariinae (Orchidaceae)

Leaves of Habenariinae are characterized by anomocytic stomatal apparatuses, homogeneous mesophyll, collateral vascular bundles in a single series, and thin-walled bundle sheath cells. There is no foliar sclerenchyma nor a hypodermis. Cauline cortex consists of thin-walled living cells among which are large and numerous intercellular spaces. The ground tissue is bordered externally by a layer of thick-walled living cells, except in Habenaria repens. Central ground tissue cells are living, and usually thin-walled surrounding intercellular spaces of various dimensions. These are conspicuously large in H. repens. Collateral vascular bundles are scattered across the ground tissue. Sclerenchyma is absent. Absorbing roots are generally velamentous, exodermal dead cells are diin-walled, and passage cells usually have a thickened outer wall. A regular vascular cylinder is present, and vascular tissue is embedded in parenchyma. Root tubers are velamentous, exodermal cells are usually thin-walled, and passage cells frequently have thickened outer walls. Vascular tissue of root tubers is organized into two classes: (1) those with a single vascular cylinder surrounded by a cortex and (2) those with a series of meristeles dispersed throughout the ground tissue. In group (1) cortex is homogeneous either with or without mucilage cells except in Stenoglattis where the cortex is heterogeneous, consisting of water-storage and assimilatory cells, and lacks mucilage cells. In group (2) the ground tissue consists of larger mucilage-containing cells and smaller assimilatory cells.     

Systematic leaf anatomy of Caladeniinae (Orchidaceae)

Leaf anatomy of 25 species in 15 genera of Caladeniinae (Diurideae, Orchidaceae), excluding Caladenia, was investigated to determine diagnostic characters to be used in forthcoming, broad-based cladistic analyses of the subtribe and to assess interspecific and intergeneric relationshipS. Of the characters examined, those that show the most variation among the study taxa are presence and types of trichomes, cuticular sculpturing, anticlinal walls of epidermal cells, heterogeneity of chlorenchyma, distribution and length: width ratios of stomata. Anatomical evidence supports the generic concept of Leptoceras Lindley but contradicts that of Drakonorchis Hopper & A.P. Brown. Paracaleana is not sufficiently distinct from Caleana to warrant generic status. Lyperanthus serratus and L.suaveolens are hyperstomatic, a rare condition in Orchidaceae. On the basis of these and other characters, Lyperanthus, as currently circumscribed, is polyphyletic. From leaf structure Caladeniinae as now conceived is polyphyletic and comprises seven groups: (1) Caladenia, Leptoceras, Elythranthera, Eriochilus, Glossodia, Aporostylis; (2) Adenochilus, Rimacola; (3) Arthrochilus, Chiloglottis, Spiculaea, Leporella; (4) Caleana (including Paracaleana); (5) Bumettia; (6) Lyperanthus suaveolens and L.serratus; (7) Lyperanthus nigricans.     

Configuration of the digestive tube as an aid to identification of worker Termitidae (Isoptera)

Abstract. The appearance of the digestive tube in situ is shown to be valuable in the identification of worker termites, particularly those of detritus and soil feeding species. Genera, and sometimes species, can be identified by this character. These preliminary findings will be of assistance to termite ecologists interested in population studies, where problems of the identification of mixed samples containing workers from cores or other soil samples are a serious problem.     

Earliest orchid macrofossils: Early Miocene Dendrobium and Earina (Orchidaceae: Epidendroideae) from New Zealand

Fossil leaves of two Early Miocene orchids (Dendrobium and Earina) are reported from New Zealand. The distinctive, raised tetra- to cyclocytic stomatal subsidiary cells of Earina and characteristic papilla-like absorbing glands and "ringed" guard cells of Dendrobium support the placement of the fossils into these genera. These therefore represent the first Orchidaceae macrofossils with cuticular preservation, the oldest records for subfamily Epidendroideae, as well as the first New Zealand and southern hemisphere fossil records for Orchidaceae. These taxa belong in basal clades to the Vandeae/Cymbideae or Epidendreae (Earina) and the Australasian clade of Dendrobium sensu lato. This phylogenetic placement demonstrates expansion of epiphytic orchids into Zealandia by the mid-Cenozoic and an important role for southern continents in the diversification of Orchidaceae.