Phylogenetic constrains on mycorrhizal specificity in eight Dendrobium(Orchidaceae) species

Plant phylogeny constrains orchid mycorrhizal(OrM) fungal community composition in some orchids. Here, we investigated the structures of the OrM fungal communities of eight Dendrobium species in one niche to determine whether similarities in the OrM fungal communities correlated with the phylogeny of the host plants and whether the Dendrobium-OrM fungal interactions are phylogenetically conserved. A phylogeny based on DNA data was constructed for the eight coexisting Dendrobium species,and the OrM fungal communities were characterized by their roots. There were 31 different fungal lineages associated with the eight Dendrobium species. In total, 82.98% of the identified associations belonging to Tulasnellaceae, and a smaller proportion involved members of the unknown Basidiomycota(9.67%). Community analyses revealed that phylogenetically related Dendrobium tended to interact with a similar set of Tulasnellaceae fungi. The interactions between Dendrobium and Tulasnellaceae fungi were significantly influenced by the phylogenetic relationships among the Dendrobium species. Our results provide evidence that the mycorrhizal specificity in the eight coexisting Dendrobium species was phylogenetically conserved.     

The genus Mesadenella (Orchidaceae) in Colombia with description of two new species

Two new species of Mesadenella, M. longipetiolata and M. bicordata, are described, illustrated and placed within the key to identification of Colombian Mesadenella species. The information about distribution and ecology of the new species as well as brief taxonomic notes are provided.     

Incompatibility in Dendrobium (Orchidaceae)

JOHANSEN, B., 1990. Incompatibility in Dendrobium (Orchidaceae). A unique self-incompatibility system in Dendrobium is demonstrated by more than 1700 pollination experiments. The majority (72%) of the 61 species that were self-pollinated showed self-sterility. In contrast with many other orchid genera Dendrobium showed high incompatibility in interspecific pollinations. Self-and interspecific incompatibility is expressed by flower abscission and not by inhibition of pollen germination or pollen tube growth. The incompatibility system is gametophytic and complementary, and it is likely that the auxin content in the pollinia triggers the incompatibility reaction. Microscopical investigations on the detached cells of the stigma (here called eleutherocytes) after compatible and incompatible pollinations, suggest that the incompatibility response is probably controlled by these cells.     

New species of the genus Epistephium (Orchidaceae, Vanilloideae)

The morphological study of the herbarium material representing Epistephium (Orchidaceae, Vanilloideae) led to the discovery of two groups of specimens that significantly differ from all known species of the genus. The results of literature data study and of comparative analysis of those and other specimens suggest that these collections represent new taxa that we describe as E. garayi and E. kubiyuense. The distinguishing features of the species are indicated. As both new species are reported from Colombia (E. garayi, also from Guyana), the key for the determination of all Colombian representatives of the genus is included. Information on the ecology and distribution of newly described taxa is presented.     

A new species of Dendrobium (Orchidaceae) from Andaman Islands, India

A new species, Dendrobium gunnarii P. S. N. Rao, so far endemic to the virgin forests of Andaman Islands is described and illustrated. Affinities with the distantly related species D. wilmsianum Schltr. in section Stachyobium are dicussed.     

Analysis of network architecture reveals phylogenetic constraints on mycorrhizal specificity in the genus Orchis (Orchidaceae)

The specificity of orchids for their fungi can vary substantially, from highly specialist interactions to more generalist interactions, but little is known about the evolutionary history of the mycorrhizal specificity of orchids. Here, we used a network analysis approach to investigate orchid mycorrhizal associations in 16 species of the genus Orchis sampled across 11 different regions in Europe. We first examined in detail the structure of the network of associations and then tested for a phylogenetic signal in mycorrhizal specificity and identified the fungi with which the orchids associated. We found 20 different fungal lineages that associated with species of the genus Orchis, most of them being related to members of the Tulasnellaceae (84.33% of all identified associations) and a smaller proportion being related to members of the Ceratobasidiaceae (9.97%). Species associations formed a nested network that is built on asymmetric links among species. Evolution of mycorrhizal specificity in Orchis closely resembles a Brownian motion process, and the interaction between Orchis and Tulasnellaceae fungi is significantly influenced by the phylogenetic relationships between the Orchis species. Our results provide evidence of the presence of phylogenetic conservatism in mycorrhizal specificity in orchids and demonstrate that evolutionary processes may be an important factor in generating patterns of mycorrhizal associations.     

New species of the genus Cranichis (Orchidaceae, Cranichidinae) from Colombia

Two new species of the Neotropical genus Cranichis are described: Cranichis carlos-parrae Szlach. & Kolan. and Cranichis zarucchii Szlach. & Kolan. Both species are known exclusively from the Colombian Andes, where they were found growing in montane forests and paramo above 2,550 m of elevation. Each species is described and illustrated, and the habitat and distribution data are provided. A distribution map of the new species is presented. A dichotomous key for identification Colombian species of Cranichis is provided.     

Chromosomal diversity in two synchronopatric species of Hoffmannseggella (Orchidaceae)

Hoffmannseggella viridiflora Verola & Semir (Laeliinae, Orchidaceae) is a recently discovered species in the campos rupestres vegetation of the Espinhaço Range, MG, Brazil, in synchronopatry with H. bradei (Pabst) V. P. Castro & Chiron. Both morphological and phenological studies indicate that these species are closely related. To substantiate the differentiation of these two species we examined their chromosome numbers and morphologies. The two species had different chromosome numbers, with H. bradei having 2n = 40 and H. viridiflora having 2n = 44 chromosomes, an aneuploid number not previously documented in the genus. Meiotic behavioral studies undertaken with H. bradei revealed many abnormalities related to bivalent numbers and chromosome migration, suggesting that meiotic abnormalities could generate aneuploid gametes and perhaps aneuploid zygotes. Karyotype formulas and chromosome morphologies are quite different between the species, so H. viridiflora was not directly derived from H. bradei through simple chromosome additions. Complementary analyses are necessary to understand the process and species involved in the origin of H. viridiflora.     

A new species of Dendrobium (Orchidaceae) from Great Nicobar Island, India

Dendrobium shompenii is described and illustrated as a new species from Great Nicobar Island, India. Affinities with the closely related species Dendrobium nathanielis are discussed.     

The genus Chamaegastrodia (Orchidaceae)

A merger of the genera Evrardia and Chamaegastrodia is proposed, and an annotated enumeration of five species so far recognized is proposed.     

Low specificity and nested subset structure characterize mycorrhizal associations in five closely related species of the genus Orchis

Most orchid species rely on mycorrhizae to complete their life cycle. Despite a growing body of literature identifying orchid mycorrhizal associations, the nature and specificity of the association between orchid species and mycorrhizal fungi remains largely an open question. Nonetheless, better insights into these obligate plant–fungus associations are indispensable for understanding the biology and conservation of orchid populations. To investigate orchid mycorrhizal associations in five species of the genus Orchis (O. anthropophora, O. mascula, O. militaris, O. purpurea, and O. simia), we developed internal transcribed spacer‐based DNA arrays from extensive clone library sequence data sets, enabling rapid and simultaneous detection of a wide range of basidiomycetous mycorrhizal fungi. A low degree of specificity was observed, with two orchid species associating with nine different fungal partners. Phylogenetic analysis revealed that the majority of Orchis mycorrhizal fungi are members of the Tulasnellaceae, but in some plants, members of the Thelephoraceae, Cortinariaceae and Ceratobasidiaceae were also found. In all species except one (O. mascula), individual plants associated with more than one fungus simultaneously, and in some cases, associations with ≥3 mycorrhizal fungi at the same time were identified. Nestedness analysis showed that orchid mycorrhizal associations were significantly nested, suggesting asymmetric specialization and a dense core of interactions created by symmetric interactions between generalist species. Our results add support to the growing literature that multiple associations may be common among orchids. Low specificity or preference for a widespread fungal symbiont may partly explain the wide distribution of the investigated species.     

Transitions between self-compatibility and self-incompatibility and the evolution of reproductive isolation in the large and diverse tropical genus Dendrobium (Orchidaceae)

Background and Aims The evolution of interspecific reproductive barriers is crucial to understanding species evolution. This study examines the contribution of transitions between self-compatibility (SC) and self-incompatibility (SI) and genetic divergence in the evolution of reproductive barriers in Dendrobium, one of the largest orchid genera. Specifically, it investigates the evolution of pre- and postzygotic isolation and the effects of transitions between compatibility states on interspecific reproductive isolation within the genus.Methods The role of SC and SI changes in reproductive compatibility among species was examined using fruit set and seed viability data available in the literature from 86 species and ∼2500 hand pollinations. The evolution of SC and SI in Dendrobium species was investigated within a phylogenetic framework using internal transcribed spacer sequences available in GenBank.Key Results Based on data from crossing experiments, estimations of genetic distance and the results of a literature survey, it was found that changes in SC and SI significantly influenced the compatibility between species in interspecific crosses. The number of fruits produced was significantly higher in crosses in which self-incompatible species acted as pollen donor for self-compatible species, following the SI × SC rule. Maximum likelihood and Bayesian tests did not reject transitions from SI to SC and from SC to SI across the Dendrobium phylogeny. In addition, postzygotic isolation (embryo mortality) was found to evolve gradually with genetic divergence, in agreement with previous results observed for other plant species, including orchids.Conclusions Transitions between SC and SI and the gradual accumulation of genetic incompatibilities affecting postzygotic isolation are important mechanisms preventing gene flow among Dendrobium species, and may constitute important evolutionary processes contributing to the high levels of species diversity in this tropical orchid group.     

Two new species of the genus Pelexia (Orchidaceae, Spiranthinae) from South America

Szlachetko, D. L. 1995. Two new species of the genus Pelexia (Orchidaceae, Spiranthinae) from South America. - Nord. J. Bot. 15: 173–175. Copenhagen. ISSN 0107–055X.
Pelexia sheviakii and Pelexia collocaliae are described as new species from Ecuador and Paraguay respectively. Pelexia sheviakii differs from Pelexia bonariensis and any other species related by its lip form, which is rhomboid, has no constriction, and with basal lip thickenings produced on upper surface of claw. The most characteristic features of Pelexia collocaliae are U-shaped callus at apices of petals, erect flowers, straight lateral sepals and narrow lip with two small calli near isthmus.     

Studies in the genus Nervilia (Orchidaceae) in Africa

Taxonomy and nomenclature of six Nervilia species occurring in the Flora Zambesiaca area are revised. Lectotypes or neotypes are selected for all relevant taxa from Africa. The new species N. gassneri is described and the new combination N. kotschyi var. purpurata is made. One widespread African species previously mostly known under the names N. humilis and N. reniformis is shown to be conspecific with the widespread Asian and Australien species N. crociformis.     

Micropropagation and genetic stability of a Dendrobium hybrid (Orchidaceae)

Summary Dendrobium hybrids have great economic importance in a number of countries. Asymbiotic seed germination and the conventional vegetative method have been commonly used by growers to propagate these plants. To overcome somaclonal variation, which is commonly exhibited by Dendrobium (Nobile group) when micropropagated from protocorm-like bodies, a protocol for propagating Dendrobium Second Love in vitro using axillary buds in the presence of thidiazuron was developed. Random amplified polymorphic DNA analysis was also carried out to check for possible genetic alterations in plants originating from six consecutive subcultures. The results revealed that the established protocol was efficient for the in vitro cloning of this orchid hybrid and the plants obtained from the six subcultures did not exhibit any type of polymorphism.     

束花石斛种子超低温保存的研究

以濒危兰科物种野生束花石斛（Dendrobium chrysanthum）的成熟种子为材料,研究了PVS2植物玻璃化液对其萌发的作用,以及快速冷冻法和玻璃化法对种子超低温保存的影响。结果表明,种子的萌发率随着PVS2处理时间的延长而下降。PVS2预处理能明显地增加种子的超低温耐性。当预处理时间为15～45min时,种子的超低温耐性随预处理时间的延长而增加;当预处理时间长于60min后,种子的超低温耐性随预处理时间的延长而下降。经液氮保存后,存活的种子能萌发成为正常的幼苗。结论是经PVS2预处理45min后,成熟的束花石斛种子能成功地进行超低温保存。     

Evidence for two distinctive species of Pseudorchis (Orchidaceae) in Scandinavia.

Reinhammar, L.-G. 1995. Evidence for two distinct species of Pseudorchis (Orchidaceae) in Scandinavia. - Nord. J. Bot. 15: 469–481. Copenhagen. ISSN 0107–055X.
Nordic populations of Pseudorchis albida s.l. were studied for variation in morphological characters. Canonical variates analysis (CVA) arrange populations in two discrete groups, corresponding to P. albida S.S. and P. straminea , respectively. In principal component analysis (PCA) of the total material a small overlap could be seen. However, separate PCA:s on members of the two taxa from the same geographic region show perfect separation. Since the two taxa are distinct in morphology as well as in additional characters, e.g. habitat preference in the area of sympatry, they are best treated as separate species. The generic name Pseudorchis is considered to be validly published and is then preferred over the later Leucorchis . A lectotype is selected for Gymnadenia albida f. subalpina .     

Breeding systems in two species of the genus Helleborus (Ranunculaceae)

ABSTRACT

The results of various types of manual and free pollination are reported in Helleborus bocconei and Helleborus foetidus, two sympatric species of the understorey of submediterranean woods that flower in January–March and are pollinated by bumble-bees of the genus Bombus. Both species were found to be partially self-compatible even if at different rates; geitonogamy seems to be more frequent in H. foetidus and spontaneous self-pollination does not usually occur for morphological reasons, and the species are not apomictic. Efficiency in seed production after free pollination was very high indicating that in spite of harsh climatic condition, there were no limitations imposed by pollen or pollinators.     

Megasporogenesis,megagametogenesis, and embryogenesis in Dendrobium nobile (Orchidaceae)

The orchid reproductive strategy, including the formation of numerous tiny seeds, is achieved by the elimination of some stages in the early plant embryogenesis. In this study, we documented in detail the formation of the maternal tissues (the nucellus and integuments), the structures of female gametophyte (megaspores, chalazal nuclei, synergids, polar nuclei), and embryonic structures in Dendrobium nobile. The ovary is unilocular, and the ovule primordia are formed in the placenta before the pollination. The ovule is medionucellate: the two-cell postament and two rows of nucellar cells persist until the death of the inner integument. A monosporic eight-nucleated embryo sac is developed. After the fertilization, the most common central cell nucleus consisted of two joined but not fused polar nuclei. The embryogenesis of D. nobile is similar to the Caryophyllad-type, and it is characterized by the formation of all embryo cells from the apical cell (ca) of a two-celled proembryo. The only exception is that there is no formation of the radicle and/or cotyledons. The basal cell (cb) does not divide during the embryogenesis, gradually transforming into the uninuclear suspensor. Then the suspensor goes through three main stages: it starts with an unbranched cell within the embryo sac, followed by a branched stage growing into the integuments, and it ends with the cell death. The stage-specific development of the female gametophyte and embryo of D. nobile is discussed.