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Heroen Verbruggen - One of the best experts on this subject based on the ideXlab platform.
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One hundred years later, resurrection of Tydemania gardineri A. Gepp & E. Gepp (Udoteaceae, Chlorophyta) based on molecular and morphological data
European Journal of Phycology, 2019Co-Authors: Laura Lagourgue, Heroen Verbruggen, Eghbert Elvan Ampou, Claude PayriAbstract:Tydemania Weber-van Bosse is a genus belonging to the family Udoteaceae (Bryopsidales, Chlorophyta) and currently thought to be monospecific throughout its distribution range in the Indo-Pacific. W...
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Reassessment of the classification of Bryopsidales (Chlorophyta) based on chloroplast phylogenomic analyses
Molecular phylogenetics and evolution, 2018Co-Authors: Ma Chiela M Cremen, Frederik Leliaert, Juan M. López-bautista, John A. West, Daryl W. Lam, Satoshi Shimada, Heroen VerbruggenAbstract:The Bryopsidales is a morphologically diverse group of mainly marine green macroalgae characterized by a siphonous structure. The order is composed of three suborders - Ostreobineae, Bryopsidineae, and Halimedineae. While previous studies improved the higher-level classification of the order, the taxonomic placement of some genera in Bryopsidineae (Pseudobryopsis and Lambia) as well as the relationships between the families of Halimedineae remains uncertain. In this study, we re-assess the phylogeny of the order with datasets derived from chloroplast genomes, drastically increasing the taxon sampling by sequencing 32 new chloroplast genomes. The phylogenies presented here provided good support for the major lineages (suborders and most families) in Bryopsidales. In Bryopsidineae, Pseudobryopsis hainanensis was inferred as a distinct lineage from the three established families allowing us to establish the family Pseudobryopsidaceae. The Antarctic species Lambia antarctica was shown to be an early-branching lineage in the family Bryopsidaceae. In Halimedineae, we revealed several inconsistent phylogenetic positions of macroscopic taxa, and several entirely new lineages of microscopic species. A new classification scheme is proposed, which includes the merger of the families Pseudocodiaceae, Rhipiliaceae and Udoteaceae into a more broadly circumscribed Halimedaceae, and the establishment of tribes for the different lineages found therein. In addition, the deep-water genus Johnson-sea-linkia, currently placed in Rhipiliopsis, was reinstated based on our phylogeny.
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Large Diversity of Nonstandard Genes and Dynamic Evolution of Chloroplast Genomes in Siphonous Green Algae (Bryopsidales, Chlorophyta).
Genome biology and evolution, 2018Co-Authors: Ma Chiela M Cremen, Vanessa R Marcelino, Frederik Leliaert, Heroen VerbruggenAbstract:Chloroplast genomes have undergone tremendous alterations through the evolutionary history of the green algae (Chloroplastida). This study focuses on the evolution of chloroplast genomes in the siphonous green algae (order Bryopsidales). We present five new chloroplast genomes, which along with existing sequences, yield a data set representing all but one families of the order. Using comparative phylogenetic methods, we investigated the evolutionary dynamics of genomic features in the order. Our results show extensive variation in chloroplast genome architecture and intron content. Variation in genome size is accounted for by the amount of intergenic space and freestanding open reading frames that do not show significant homology to standard plastid genes. We show the diversity of these nonstandard genes based on their conserved protein domains, which are often associated with mobile functions (reverse transcriptase/intron maturase, integrases, phage- or plasmid-DNA primases, transposases, integrases, ligases). Investigation of the introns showed proliferation of group II introns in the early evolution of the order and their subsequent loss in the core Halimedineae, possibly through RT-mediated intron loss.
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Codium pulvinatum (Bryopsidales, Chlorophyta), a new species from the Arabian Sea, recently introduced into the Mediterranean Sea
Phycologia, 2018Co-Authors: Razy Hoffman, Tom Schils, Juan M. López-bautista, Michael J. Wynne, Heroen VerbruggenAbstract:Abstract Codium pulvinatum sp. nov. (Bryopsidales, Chlorophyta) is described from the southern shores of Oman and from the Mediterranean shore of Israel. The new species has a pulvinate to mamillate–globose habit and long narrow utricles. Molecular data from the rbcL gene show that the species is distinct from closely related species, and concatenated rbcL and rps3–rpl16 sequence data show that it is not closely related to other species with similar external morphologies. The recent discovery of well-established populations of C. pulvinatum along the central Mediterranean coast of Israel suggests that it is a new Lessepsian migrant into the Mediterranean Sea. The ecology and invasion success of the genus Codium, now with four alien species reported for the Levantine Sea, and some ecological aspects are also discussed in light of the discovery of the new species.
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Phylogenetic position of the coral symbiont Ostreobium (Ulvophyceae) inferred from chloroplast genome data.
Journal of phycology, 2017Co-Authors: Heroen Verbruggen, Ma Chiela M Cremen, Vanessa R Marcelino, Michael D. Guiry, Christopher J. JacksonAbstract:The green algal genus Ostreobium is an important symbiont of corals, playing roles in reef decalcification and providing photosynthates to the coral during bleaching events. A chloroplast genome of a cultured strain of Ostreobium was available, but low taxon sampling and Ostreobium's early-branching nature left doubt about its phylogenetic position. Here, we generate and describe chloroplast genomes from four Ostreobium strains as well as Avrainvillea mazei and Neomeris sp., strategically sampled early-branching lineages in the Bryopsidales and Dasycladales respectively. At 80,584 bp, the chloroplast genome of Ostreobium sp. HV05042 is the most compact yet found in the Ulvophyceae. The Avrainvillea chloroplast genome is ~94 kbp and contains introns in infA and cysT that have nearly complete sequence identity except for an open reading frame (ORF) in infA that is not present in cysT. In line with other bryopsidalean species, it also contains regions with possibly bacteria-derived ORFs. The Neomeris data did not assemble into a canonical circular chloroplast genome but a large number of contigs containing fragments of chloroplast genes and showing evidence of long introns and intergenic regions, and the Neomeris chloroplast genome size was estimated to exceed 1.87 Mb. Chloroplast phylogenomics and 18S nrDNA data showed strong support for the Ostreobium lineage being sister to the remaining Bryopsidales. There were differences in branch support when outgroups were varied, but the overall support for the placement of Ostreobium was strong. These results permitted us to validate two suborders and introduce a third, the Ostreobineae.
Frederik Leliaert - One of the best experts on this subject based on the ideXlab platform.
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Diversity of Sulfated Polysaccharides From Cell Walls of Coenocytic Green Algae and Their Structural Relationships in View of Green Algal Evolution
Frontiers in plant science, 2020Co-Authors: Marina Ciancia, Paula Virginia Fernández, Frederik LeliaertAbstract:Seaweeds biosynthesize sulfated polysaccharides as key components of their cell walls. These polysaccharides are potentially interesting as biologically active compounds. Green macroalgae of the class Ulvophyceae comprise sulfated polysaccharides with great structural differences regarding the monosaccharide constituents, linearity of their backbones, and presence of other acidic substituents in their structure, including uronic acid residues and pyruvic acid. These structures have been thoroughly studied in the Ulvales and Ulotrichales, but only more recently have they been investigated with some detail in ulvophytes with giant multinucleate (coenocytic) cells, including the siphonous Bryopsidales and Dasycladales, and the siphonocladous Cladophorales. An early classification of these structurally heterogeneous polysaccharides was based on the presence of uronic acid residues in these molecules. In agreement with this classification based on chemical structures, sulfated polysaccharides of the orders Bryopsidales and Cladophorales fall in the same group, in which this acidic component is absent, or only present in very low quantities. The cell walls of Dasycladales have been less studied, and it remains unclear if they comprise sulfated polysaccharides of both types. Although in the Bryopsidales and Cladophorales the most important sulfated polysaccharides are arabinans and galactans (or arabinogalactans), their major structures are very different. The Bryopsidales produce sulfated pyruvylated 3-linked β-d-galactans, in most cases, with ramifications on C6. For some species, linear sulfated pyranosic β-l-arabinans have been described. In the Cladophorales, also sulfated pyranosic β-l-arabinans have been found, but 4-linked and highly substituted with side chains. These differences are consistent with recent molecular phylogenetic analyses, which indicate that the Bryopsidales and Cladophorales are distantly related. In addition, some of the Bryopsidales also biosynthesize other sulfated polysaccharides, i.e., sulfated mannans and sulfated rhamnans. The presence of sulfate groups as a distinctive characteristic of these biopolymers has been related to their adaptation to the marine environment. However, it has been shown that some freshwater algae from the Cladophorales also produce sulfated polysaccharides. In this review, structures of sulfated polysaccharides from bryopsidalean, dasycladalean, and cladophoralean green algae studied until now are described and analyzed based on current phylogenetic understanding, with the aim of unveiling the important knowledge gaps that still exist.
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Reassessment of the classification of Bryopsidales (Chlorophyta) based on chloroplast phylogenomic analyses
Molecular phylogenetics and evolution, 2018Co-Authors: Ma Chiela M Cremen, Frederik Leliaert, Juan M. López-bautista, John A. West, Daryl W. Lam, Satoshi Shimada, Heroen VerbruggenAbstract:The Bryopsidales is a morphologically diverse group of mainly marine green macroalgae characterized by a siphonous structure. The order is composed of three suborders - Ostreobineae, Bryopsidineae, and Halimedineae. While previous studies improved the higher-level classification of the order, the taxonomic placement of some genera in Bryopsidineae (Pseudobryopsis and Lambia) as well as the relationships between the families of Halimedineae remains uncertain. In this study, we re-assess the phylogeny of the order with datasets derived from chloroplast genomes, drastically increasing the taxon sampling by sequencing 32 new chloroplast genomes. The phylogenies presented here provided good support for the major lineages (suborders and most families) in Bryopsidales. In Bryopsidineae, Pseudobryopsis hainanensis was inferred as a distinct lineage from the three established families allowing us to establish the family Pseudobryopsidaceae. The Antarctic species Lambia antarctica was shown to be an early-branching lineage in the family Bryopsidaceae. In Halimedineae, we revealed several inconsistent phylogenetic positions of macroscopic taxa, and several entirely new lineages of microscopic species. A new classification scheme is proposed, which includes the merger of the families Pseudocodiaceae, Rhipiliaceae and Udoteaceae into a more broadly circumscribed Halimedaceae, and the establishment of tribes for the different lineages found therein. In addition, the deep-water genus Johnson-sea-linkia, currently placed in Rhipiliopsis, was reinstated based on our phylogeny.
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Large Diversity of Nonstandard Genes and Dynamic Evolution of Chloroplast Genomes in Siphonous Green Algae (Bryopsidales, Chlorophyta).
Genome biology and evolution, 2018Co-Authors: Ma Chiela M Cremen, Vanessa R Marcelino, Frederik Leliaert, Heroen VerbruggenAbstract:Chloroplast genomes have undergone tremendous alterations through the evolutionary history of the green algae (Chloroplastida). This study focuses on the evolution of chloroplast genomes in the siphonous green algae (order Bryopsidales). We present five new chloroplast genomes, which along with existing sequences, yield a data set representing all but one families of the order. Using comparative phylogenetic methods, we investigated the evolutionary dynamics of genomic features in the order. Our results show extensive variation in chloroplast genome architecture and intron content. Variation in genome size is accounted for by the amount of intergenic space and freestanding open reading frames that do not show significant homology to standard plastid genes. We show the diversity of these nonstandard genes based on their conserved protein domains, which are often associated with mobile functions (reverse transcriptase/intron maturase, integrases, phage- or plasmid-DNA primases, transposases, integrases, ligases). Investigation of the introns showed proliferation of group II introns in the early evolution of the order and their subsequent loss in the core Halimedineae, possibly through RT-mediated intron loss.
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Systematics and biogeography of the genus Pseudocodium (Bryopsidales, Chlorophyta), including the description of P. natalense sp. nov. from South Africa
2016Co-Authors: Olivier De Clerck, John M Huisman, Tom Schils, Eric Coppejans, Frederik Leliaert, Heroen Verbruggen, Etienne J. FayeAbstract:Systematics and biogeography of the genus Pseudocodium (Bryopsidales, Chlorophyta), including the description o
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The chloroplast genomes of Bryopsis plumosa and Tydemania expeditiones (Bryopsidales, Chlorophyta): compact genomes and genes of bacterial origin
BMC genomics, 2015Co-Authors: Frederik Leliaert, Juan M. López-bautistaAbstract:Species of Bryopsidales form ecologically important components of seaweed communities worldwide. These siphonous macroalgae are composed of a single giant tubular cell containing millions of nuclei and chloroplasts, and harbor diverse bacterial communities. Little is known about the diversity of chloroplast genomes (cpDNAs) in this group, and about the possible consequences of intracellular bacteria on genome composition of the host. We present the complete cpDNAs of Bryopsis plumosa and Tydemania expeditiones, as well as a re-annotated cpDNA of B. hypnoides, which was shown to contain a higher number of genes than originally published. Chloroplast genomic data were also used to evaluate phylogenetic hypotheses in the Chlorophyta, such as monophyly of the Ulvophyceae (the class in which the order Bryopsidales is currently classified). Both DNAs are circular and lack a large inverted repeat. The cpDNA of B. plumosa is 106,859 bp long and contains 115 unique genes. A 13 kb region was identified with several freestanding open reading frames (ORFs) of putative bacterial origin, including a large ORF (>8 kb) closely related to bacterial rhs-family genes. The cpDNA of T. expeditiones is 105,200 bp long and contains 125 unique genes. As in B. plumosa, several regions were identified with ORFs of possible bacterial origin, including genes involved in mobile functions (transposases, integrases, phage/plasmid DNA primases), and ORFs showing close similarity with bacterial DNA methyltransferases. The cpDNA of B. hypnoides differs from that of B. plumosa mainly in the presence of long intergenic spacers, and a large tRNA region. Chloroplast phylogenomic analyses were largely inconclusive with respect to monophyly of the Ulvophyceae, and the relationship of the Bryopsidales within the Chlorophyta. The cpDNAs of B. plumosa and T. expeditiones are amongst the smallest and most gene dense chloroplast genomes in the core Chlorophyta. The presence of bacterial genes, including genes typically found in mobile elements, suggest that these have been acquired through horizontal gene transfer, which may have been facilitated by the occurrence of obligate intracellular bacteria in these siphonous algae.
Mark M. Littler - One of the best experts on this subject based on the ideXlab platform.
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A multi-locus time-calibrated phylogeny of the siphonous green algae
Molecular phylogenetics and evolution, 2008Co-Authors: Heroen Verbruggen, Thomas Sauvage, Mark M. Littler, Diane S. Littler, Matt P. Ashworth, Steven T. Loduca, Caroline Vlaeminck, Ellen Cocquyt, Frederick W. Zechman, Frederik LeliaertAbstract:The siphonous green algae are an assemblage of seaweeds that consist of a single giant cell. They comprise two sister orders, the Bryopsidales and Dasycladales. We infer the phylogenetic relationships among the siphonous green algae based on a five-locus data matrix and analyze temporal aspects of their diversification using relaxed molecular clock methods calibrated with the fossil record. The multi-locus approach resolves much of the previous phylogenetic uncertainty, but the radiation of families belonging to the core Halimedineae remains unresolved. In the Bryopsidales, three main clades were inferred, two of which correspond to previously described suborders (Bryopsidineae and Halimedineae) and a third lineage that contains only the limestone-boring genus Ostreobium. Relaxed molecular clock models indicate a Neoproterozoic origin of the siphonous green algae and a Paleozoic diversification of the orders into their families. The inferred node ages are used to resolve conflicting hypotheses about species ages in the tropical marine alga Halimeda.
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halimeda pygmaea and halimeda pumila Bryopsidales chlorophyta two new dwarf species from fore reef slopes in fiji and the bahamas
Phycologia, 2007Co-Authors: Heroen Verbruggen, Diane S. Littler, Mark M. LittlerAbstract:H. VERBRUGGEN, D.S. LITTLER AND M.M. LITTLER. 2007. Halimeda pygmaea and Halimeda pumila (Bryopsidales, Chlorophyta): two new dwarf species from fore reef slopes in Fiji and the Bahamas. Phycologia 46: 513–520. DOI: 10.2216/07-01.1 Halimeda pygmaea and Halimeda pumila, two diminutive calcified green algal species, are described from material collected on Fijian and Bahamian reef slopes, respectively. The species resemble Halimeda cryptica in having a single siphon traversing the nodes between subsequent calcified segments and living in sheltered fore-reef slope habitats. They differ from H. cryptica by their diminutive size and various anatomical features. Molecular sequence data (tufA) underpin the identity of H. pygmaea and reveal its phylogenetic position as a sister taxon to H. cryptica in the Halimeda section Micronesicae.
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halimeda pygmaea and halimeda pumila Bryopsidales chlorophyta two new dwarf species from fore reef slopes in fiji and the bahamas
Phycologia, 2007Co-Authors: Heroen Verbruggen, Diane S. Littler, Mark M. LittlerAbstract:H. VERBRUGGEN, D.S. LITTLER AND M.M. LITTLER. 2007. Halimeda pygmaea and Halimeda pumila (Bryopsidales, Chlorophyta): two new dwarf species from fore reef slopes in Fiji and the Bahamas. Phycologia 46: 513–520. DOI: 10.2216/07-01.1 Halimeda pygmaea and Halimeda pumila, two diminutive calcified green algal species, are described from material collected on Fijian and Bahamian reef slopes, respectively. The species resemble Halimeda cryptica in having a single siphon traversing the nodes between subsequent calcified segments and living in sheltered fore-reef slope habitats. They differ from H. cryptica by their diminutive size and various anatomical features. Molecular sequence data (tufA) underpin the identity of H. pygmaea and reveal its phylogenetic position as a sister taxon to H. cryptica in the Halimeda section Micronesicae.
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Systematics of Avrainvillea (Bryopsidales, Chlorophyta) in the tropical western Atlantic
Phycologia, 1992Co-Authors: Diane S. Littler, Mark M. LittlerAbstract:Twenty-one specific and infraspecific taxa of the genus Avrainvillea from the tropical western Atlantic are treated. Six new species (Avrainvillea digitata, A. fenicalii, A. fulva, A. hayi, A. silv...
Diane S. Littler - One of the best experts on this subject based on the ideXlab platform.
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A multi-locus time-calibrated phylogeny of the siphonous green algae
Molecular phylogenetics and evolution, 2008Co-Authors: Heroen Verbruggen, Thomas Sauvage, Mark M. Littler, Diane S. Littler, Matt P. Ashworth, Steven T. Loduca, Caroline Vlaeminck, Ellen Cocquyt, Frederick W. Zechman, Frederik LeliaertAbstract:The siphonous green algae are an assemblage of seaweeds that consist of a single giant cell. They comprise two sister orders, the Bryopsidales and Dasycladales. We infer the phylogenetic relationships among the siphonous green algae based on a five-locus data matrix and analyze temporal aspects of their diversification using relaxed molecular clock methods calibrated with the fossil record. The multi-locus approach resolves much of the previous phylogenetic uncertainty, but the radiation of families belonging to the core Halimedineae remains unresolved. In the Bryopsidales, three main clades were inferred, two of which correspond to previously described suborders (Bryopsidineae and Halimedineae) and a third lineage that contains only the limestone-boring genus Ostreobium. Relaxed molecular clock models indicate a Neoproterozoic origin of the siphonous green algae and a Paleozoic diversification of the orders into their families. The inferred node ages are used to resolve conflicting hypotheses about species ages in the tropical marine alga Halimeda.
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halimeda pygmaea and halimeda pumila Bryopsidales chlorophyta two new dwarf species from fore reef slopes in fiji and the bahamas
Phycologia, 2007Co-Authors: Heroen Verbruggen, Diane S. Littler, Mark M. LittlerAbstract:H. VERBRUGGEN, D.S. LITTLER AND M.M. LITTLER. 2007. Halimeda pygmaea and Halimeda pumila (Bryopsidales, Chlorophyta): two new dwarf species from fore reef slopes in Fiji and the Bahamas. Phycologia 46: 513–520. DOI: 10.2216/07-01.1 Halimeda pygmaea and Halimeda pumila, two diminutive calcified green algal species, are described from material collected on Fijian and Bahamian reef slopes, respectively. The species resemble Halimeda cryptica in having a single siphon traversing the nodes between subsequent calcified segments and living in sheltered fore-reef slope habitats. They differ from H. cryptica by their diminutive size and various anatomical features. Molecular sequence data (tufA) underpin the identity of H. pygmaea and reveal its phylogenetic position as a sister taxon to H. cryptica in the Halimeda section Micronesicae.
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halimeda pygmaea and halimeda pumila Bryopsidales chlorophyta two new dwarf species from fore reef slopes in fiji and the bahamas
Phycologia, 2007Co-Authors: Heroen Verbruggen, Diane S. Littler, Mark M. LittlerAbstract:H. VERBRUGGEN, D.S. LITTLER AND M.M. LITTLER. 2007. Halimeda pygmaea and Halimeda pumila (Bryopsidales, Chlorophyta): two new dwarf species from fore reef slopes in Fiji and the Bahamas. Phycologia 46: 513–520. DOI: 10.2216/07-01.1 Halimeda pygmaea and Halimeda pumila, two diminutive calcified green algal species, are described from material collected on Fijian and Bahamian reef slopes, respectively. The species resemble Halimeda cryptica in having a single siphon traversing the nodes between subsequent calcified segments and living in sheltered fore-reef slope habitats. They differ from H. cryptica by their diminutive size and various anatomical features. Molecular sequence data (tufA) underpin the identity of H. pygmaea and reveal its phylogenetic position as a sister taxon to H. cryptica in the Halimeda section Micronesicae.
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Systematics of Avrainvillea (Bryopsidales, Chlorophyta) in the tropical western Atlantic
Phycologia, 1992Co-Authors: Diane S. Littler, Mark M. LittlerAbstract:Twenty-one specific and infraspecific taxa of the genus Avrainvillea from the tropical western Atlantic are treated. Six new species (Avrainvillea digitata, A. fenicalii, A. fulva, A. hayi, A. silv...
Reinhard Schnetter - One of the best experts on this subject based on the ideXlab platform.
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revision of the pseudobryopsis trichosolen complex Bryopsidales chlorophyta based on features of gametangial behavior and chloroplasts
Phycologia, 1999Co-Authors: Katharina-dorothee Henne, Reinhard SchnetterAbstract:Abstract Two combinations of features exist in species of the Pseudobryopsis/Trichosolen complex (Bryopsidales, Chlorophyta): (1) gametangia are separated from the supporting branch by a plug and are emptied after liberation of gametes; chloroplasts are small and have no pyrenoids; and (2) gametangia have a protoplasmic connection to the supporting branch during their entire development and are refilled with protoplasm after liberation of gametes; chloroplasts are large and have evident pyrenoids. Culture studies in Pseudobryopsis oahuensis Egerod and Trichosolen duchassaingii (J. Agardh) Taylor showed that these species differ considerably in chloroplast features and gametangial behavior. Examination of herbarium material of P. blomquistii Diaz-Piferrer, T. duchassaingii (J. Agardh) Taylor, P. gracilis Womersley et Bailey, P. longipedicellata Blomquist et Diaz-Piferrer, P. mauritiana Borgesen, T. molassensis Bucher et Norris, P. myura (J. Agardh) Berthold, P. oahuensis Egerod, P. parva Dawson, P. planklo...
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Revision of the Pseudobryopsis/Trichosolen complex (Bryopsidales, Chlorophyta) based on features of gametangial behavior and chloroplasts
Phycologia, 1999Co-Authors: Katharina-dorothee Henne, Reinhard SchnetterAbstract:Abstract Two combinations of features exist in species of the Pseudobryopsis/Trichosolen complex (Bryopsidales, Chlorophyta): (1) gametangia are separated from the supporting branch by a plug and are emptied after liberation of gametes; chloroplasts are small and have no pyrenoids; and (2) gametangia have a protoplasmic connection to the supporting branch during their entire development and are refilled with protoplasm after liberation of gametes; chloroplasts are large and have evident pyrenoids. Culture studies in Pseudobryopsis oahuensis Egerod and Trichosolen duchassaingii (J. Agardh) Taylor showed that these species differ considerably in chloroplast features and gametangial behavior. Examination of herbarium material of P. blomquistii Diaz-Piferrer, T. duchassaingii (J. Agardh) Taylor, P. gracilis Womersley et Bailey, P. longipedicellata Blomquist et Diaz-Piferrer, P. mauritiana Borgesen, T. molassensis Bucher et Norris, P. myura (J. Agardh) Berthold, P. oahuensis Egerod, P. parva Dawson, P. planklo...
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Life history and karyology of Bryopsis plumosa (Chlorophyta, Bryopsidales) from the Canary Islands
Phycologia, 1997Co-Authors: B. Brück, Reinhard SchnetterAbstract:Abstract In the microthallus of Bryopsis plumosa (Hudson) C. Agardh (Chlorophyta, Bryopsidales) from La Gomera, we show that the secondary nuclei are diploid through most multinucleate stages. Haploid nuclei can be found very late in the development of the microthallus. We conclude from these findings that the formation and multiplication of secondary nuclei is due to mitosis. Therefore, the microthallus is a true sporophyte and not merely an enlarged zygote. Meiosis is probably the last division of the secondary nuclei before zoospore formation. In macrothalli, a direct development of microthalli without prior production and fusion of gametes has been observed. This process is connected to the formation of diploid nuclei. In the Bryopsis strain that we studied, nuclear volume is not directly related to nuclear DNA content.
