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Paul A. Broady - One of the best experts on this subject based on the ideXlab platform.
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Molecular phylogeny and evolution of the order Tribonematales (Heterokonta, Xanthophyceae) based on analysis of plastidial genes rbcL and psaA.
Molecular phylogenetics and evolution, 2007Co-Authors: S. Maistro, Paul A. Broady, Carlo Andreoli, Enrico Massimiliano NegrisoloAbstract:Tribonematales is an order of filamentous algae in the class Xanthophyceae (Heterokonta). Few molecular studies, all with a limited taxon sampling, have previously investigated its evolutionary history and phylogenetic relationships. We sequenced the chloroplast-encoded rbcL and psaA genes of several tribonematalean species and of several coccoid and siphonous forms that previous studies revealed to be strictly related to Tribonematales. Multiple alignments included mostly new sequences obtained from 42 taxa. Phylogenetic reconstructions were performed using the maximum likelihood method. The rbcL and psaA data sets were analyzed independently and combined in a single multiple alignment. Neither rbcL nor psaA genes showed intraspecific sequence variation. The former proved to be a better diagnostic marker than the latter for characterization of species. We explored effects produced on phylogenetic outcomes by selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on the combined data set. There is strong statistical support for trees that show several currently recognized taxonomic groups to be polyphyletic. The siphonous orders Botrydiales and Vaucheriales do not form a clade. Botrydiales and Tribonematales are polyphyletic as are the families Botrydiaceae, Centritractaceae and Tribonemataceae and the genera Xanthonema and Bumilleriopsis. We tentatively define new boundaries of the Tribonematales to include both coccoid and filamentous species having a bipartite cell wall and also the siphonous members of the genus Botrydium. Also, our results support morphological convergence at all taxonomic ranks in the evolution of the Xanthophyceae.
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Morphological convergence characterizes the evolution of Xanthophyceae (Heterokontophyta): evidence from nuclear SSU rDNA and plastidial rbcL genes.
Molecular phylogenetics and evolution, 2004Co-Authors: Enrico Massimiliano Negrisolo, S. Maistro, M. Incarbone, Isabella Moro, Luisa Dalla Valle, Paul A. Broady, Carlo AndreoliAbstract:Xanthophyceae are a group of heterokontophyte algae. Few molecular studies have investigated the evolutionary history and phylogenetic relationships of this class. We sequenced the nuclear-encoded SSU rDNA and chloroplast-encoded rbcL genes of several xanthophycean species from different orders, families, and genera. Neither SSU rDNA nor rbcL genes show intraspecific sequence variation and are good diagnostic markers for characterization of problematic species. New sequences, combined with those previously available, were used to create different multiple alignments. Analyses included sequences from 26 species of Xanthophyceae plus three Phaeothamniophyceae and two Phaeophyceae taxa used as outgroups. Phylogenetic analyses were performed according to Bayesian inference, maximum likelihood, and maximum parsimony methods. We explored effects produced on the phylogenetic outcomes by both taxon sampling as well as selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on a data set including both SSU rDNA and rbcL sequences. Trees obtained in this study show that several currently recognized xanthophycean taxa do not form monophyletic groups. The order Mischococcales is paraphyletic, while Tribonematales and Botrydiales are polyphyletic even if evidence for the second order is not conclusive. Botrydiales and Vaucheriales, both including siphonous taxa, do not form a clade. The families Botrydiopsidaceae, Botryochloridaceae, and Pleurochloridaceae as well as the genera Botrydiopsis and Chlorellidium are polyphyletic. The Centritractaceae and the genus Bumilleriopsis also appear to be polyphyletic but their monophyly cannot be completely rejected with current evidence. Our results support morphological convergence at any taxonomic rank in the evolution of the Xanthophyceae. Finally, our phylogenetic analyses exclude an origin of the Xanthophyceae from a Vaucheria-like ancestor and favor a single early origin of the coccoid cell form.
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a comparison of strains of xanthonema heterothrix tribonematales Xanthophyceae from antarctica europe and new zealand
Phycologia, 1997Co-Authors: Paul A. Broady, Shuji Ohtani, Manfred IngerfeldAbstract:Abstract Seventeen strains of Xanthonema Silva (Tribonematales, Xanthophyceae) are examined by light microscopy and transmission electron microscopy, and their salinity tolerance is investigated. Ten strains are from Antarctica where the genus is poorly known. These strains are compared with two strains from New Zealand and five from Europe, including the only existing authentic strains of three species. Stalk-like chloroplast lobes resembling pyrenoids are described for the first time for Xanthonema. There are two types: one projects from the end of the chloroplast and the other projects from the internal face of the chloroplast into an invagination of the nuclear envelope. The latter type is a new finding for the Xanthophyceae. Xanthonema sessile (Vinatzer) Ettl et Gartner and X. hormidioides (Vischer) Silva are new records for Antarctica. Other antarctic strains resemble seven other species, but difficulties in making confident identifications are discussed. Three of the strains were unable to tolerate...
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A comparison of strains of Xanthonema (= Heterothrix, Tribonematales, Xanthophyceae) from Antarctica, Europe, and New Zealand
Phycologia, 1997Co-Authors: Paul A. Broady, Shuji Ohtani, Manfred IngerfeldAbstract:Abstract Seventeen strains of Xanthonema Silva (Tribonematales, Xanthophyceae) are examined by light microscopy and transmission electron microscopy, and their salinity tolerance is investigated. Ten strains are from Antarctica where the genus is poorly known. These strains are compared with two strains from New Zealand and five from Europe, including the only existing authentic strains of three species. Stalk-like chloroplast lobes resembling pyrenoids are described for the first time for Xanthonema. There are two types: one projects from the end of the chloroplast and the other projects from the internal face of the chloroplast into an invagination of the nuclear envelope. The latter type is a new finding for the Xanthophyceae. Xanthonema sessile (Vinatzer) Ettl et Gartner and X. hormidioides (Vischer) Silva are new records for Antarctica. Other antarctic strains resemble seven other species, but difficulties in making confident identifications are discussed. Three of the strains were unable to tolerate...
Manfred Ingerfeld - One of the best experts on this subject based on the ideXlab platform.
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a comparison of strains of xanthonema heterothrix tribonematales Xanthophyceae from antarctica europe and new zealand
Phycologia, 1997Co-Authors: Paul A. Broady, Shuji Ohtani, Manfred IngerfeldAbstract:Abstract Seventeen strains of Xanthonema Silva (Tribonematales, Xanthophyceae) are examined by light microscopy and transmission electron microscopy, and their salinity tolerance is investigated. Ten strains are from Antarctica where the genus is poorly known. These strains are compared with two strains from New Zealand and five from Europe, including the only existing authentic strains of three species. Stalk-like chloroplast lobes resembling pyrenoids are described for the first time for Xanthonema. There are two types: one projects from the end of the chloroplast and the other projects from the internal face of the chloroplast into an invagination of the nuclear envelope. The latter type is a new finding for the Xanthophyceae. Xanthonema sessile (Vinatzer) Ettl et Gartner and X. hormidioides (Vischer) Silva are new records for Antarctica. Other antarctic strains resemble seven other species, but difficulties in making confident identifications are discussed. Three of the strains were unable to tolerate...
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A comparison of strains of Xanthonema (= Heterothrix, Tribonematales, Xanthophyceae) from Antarctica, Europe, and New Zealand
Phycologia, 1997Co-Authors: Paul A. Broady, Shuji Ohtani, Manfred IngerfeldAbstract:Abstract Seventeen strains of Xanthonema Silva (Tribonematales, Xanthophyceae) are examined by light microscopy and transmission electron microscopy, and their salinity tolerance is investigated. Ten strains are from Antarctica where the genus is poorly known. These strains are compared with two strains from New Zealand and five from Europe, including the only existing authentic strains of three species. Stalk-like chloroplast lobes resembling pyrenoids are described for the first time for Xanthonema. There are two types: one projects from the end of the chloroplast and the other projects from the internal face of the chloroplast into an invagination of the nuclear envelope. The latter type is a new finding for the Xanthophyceae. Xanthonema sessile (Vinatzer) Ettl et Gartner and X. hormidioides (Vischer) Silva are new records for Antarctica. Other antarctic strains resemble seven other species, but difficulties in making confident identifications are discussed. Three of the strains were unable to tolerate...
Robert A Andersen - One of the best experts on this subject based on the ideXlab platform.
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Multigene Phylogeny, Morphological Observation and Re-examination of the Literature Lead to the Description of the Phaeosacciophyceae Classis Nova and Four New Species of the Heterokontophyta SI Clade.
Protist, 2020Co-Authors: Louis Graf, Eun Chan Yang, Kwi Young Han, Frithjof C. Küpper, Kylla Marie Benes, Jason K. Oyadomari, Roger J.h. Herbert, Heroen Verbruggen, Richard Wetherbee, Robert A AndersenAbstract:The relationships among the Aurearenophyceae, Phaeothamniophyceae, Phaeophyceae and Xanthophyceae lineages of the Heterokontophyta SI clade are not well known. By adding previously unexamined taxa related to these classes in a five gene phylogeny (SSU rRNA, atpB, psaA, psaB, rbcL), we recovered an assemblage of taxa previously unrecognized. We propose the class Phaeosacciophyceae class. nov., that includes Phaeosaccion collinsii, Phaeosaccion multiseriatum sp. nov., Phaeosaccion okellyi sp. nov., Antarctosaccion applanatum, Tetrasporopsis fuscescens, Tetrasporopsis moei sp. nov., and Psammochrysis cassiotisii gen. & sp. nov. We re-examine the literature for Chrysomeris, Nematochrysis, Chrysowaernella and the invalid name "Giraudyopsis" and conclude some taxa in previous studies are misidentified or misnamed, i.e. Chrysomeris and Chrysowaernella, respectively. We also show that Nematochrysis sessilis var. vectensis and Nematochrysis hieroglyphica may belong in the recently described class Chrysoparadoxophyceae. The phylogenetic relationships of Phaeobotrys solitaria and Pleurochloridella botrydiopsis are not clearly resolved, but they branch near the Xanthophyceae. Here we describe a new class Phaeosacciophyceae, a new order Phaeosacciales, a new family Tetrasporopsidaceae, a new genus Psammochrysis and four new species.
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Phylogenetic Analysis of the Mischococcales, Tribonematales, and Vaucheriales (Xanthophyceae) Inferred from 18S rRNA Gene Sequences
Journal of Phycology, 2002Co-Authors: A. L. Mcelhinney, J. C. Bailey, Robert A AndersenAbstract:The Xanthophyceae have traditionally been classified using a phenetic classification system based upon vegetative cell structure. Species belonging to the class are placed in one of six orders corresponding to amoeboid, coccoid, filamentous, flagellate, palmelloid, or siphonous organization. Nuclear 18S rRNA gene sequences were determined for 29 species and aligned with 10 previously determined sequences. Parsimony and maximum likelihood trees inferred from these data imply that the orders Mischococcales (coccoid), Tribonematales (filamentous), and Vaucheriales (siphonous) are not monophyletic. The majority of species are divided between two clades defined by the presence or absence of a bipartite cell wall. Also, several families, particularly those placed in the Mischococcales, are resolved as polyphyletic. Results indicate that coccoid and filamentous life forms may have arisen independently at least three times, and some coccoid and filamentous life forms are resolved as closely related. For example, Heterococcus (filamentous) is more closely related to Mischococcus and Pseudopleurochloris (coccoid) than it is to other members of the Tribonematales. Our data strongly support the contention that Bumilleriopsis and Pseudobumilleriopsis are congeneric with Bumilleria. The siphonous xanthophytes including Asterosiphon, Botrydium, and Vaucheria probably do not form a monophyletic group although robust bootstrap support for this conclusion is low. Our results indicate that the generic, familial, and ordinal classification of the Xanthophyceae requires major revision.
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MOLECULAR SYSTEMATICS OF THE Xanthophyceae
Journal of Phycology, 2000Co-Authors: J. C. Bailey, A. L. Mcelhinney, Robert A AndersenAbstract:Species belonging to the Xanthophyceae have traditionally been classified in six (or seven) orders corresponding to amoeboid, coccoid, filamentous, monadoid, palmelloid and siphonous lines of descent. We have determined plastid rbcL and nuclear 18S rRNA gene sequences for selected coccoid, filamentous and siphonous species. Phylogenetic trees inferred from these data indicate that the orders Mischococcales (coccoid) and Tribonematales (filamentous) are not monophyletic. Instead, our results indicate that coccoid and filamentous life forms have arisen independently in different xanthophyte lineages. Some coccoid and filamentous species are resolved as close allies. For example, in our analyses coccoid and filamentous species possessing bipartite cell walls (e.g., Bumilleria, Ophiocytium, Tribonema, Xanthonema) form a distinct and previously unrecognized lineage within the class. The phylogenetic positions of Asterosiphon, Botrydium and Vaucheria are not robustly resolved, but our data suggest that these siphonous xanthophytes probably do not form a monophyletic group. Our results imply that Vaucheria is only distantly related to other xanthophytes we have examined. Nucleotide sequence divergence values among Vaucheria species were found to be equal to, or greater than, those observed between other xanthophyte species that are classified in different families or orders. Furthermore, our trees do not always support the infrageneric system of classification for Vaucheria species, which is based primarily upon antheridial features.
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Phaeothamniophyceae classis nova: a new lineage of chromophytes based upon photosynthetic pigments, rbcL sequence analysis and ultrastructure
Protist, 1998Co-Authors: J. Craig Bailey, Robert R. Bidigare, Stephani J. Christensen, Robert A AndersenAbstract:A new algal class, the Phaeothamniophyceae classis nova, is established from genera formerly classified in the Chrysophyceae (e.g., Chrysapion, Chrysoclonium, Chrysodictyon, Phaeobotrys, Phaeogloea, Phaeoschizochlamys, Phaeothamnion, Selenophaea, Sphaeridiothrix, Stichogloea, Tetrachrysis, Tetrapion and Tetrasporopsis) as well as one genus previously assigned to the Xanthophyceae (Pleurochloridella). HPLC analysis revealed the presence of fucoxanthin, diadinoxanthin, diatoxanthin, β-carotene and heteroxanthin, in addition to chlorophylls a and c, in four genera (Phaeoschizochlamys, Phaeothamnion, Stichogloea, Pleurochloridella). The combination of fucoxanthin and heteroxanthin is known only for these organisms. The rbcL sequences of the same four genera, along with representatives of other chromophyte classes, were analyzed phylogenetically and provided independent support for recognition of the Phaeothamniophyceae as a distinct taxon. These data indicate that the Phaeothamniophyceae are more closely related to the classes Xanthophyceae and Phaeophyceae than to the Chrysophyceae. Electron microscopy revealed that Phaeoschizochlamys, Phaeothamnion and Stichogloea possess electron opaque vesicles at the cell periphery, have a cell wall that often appears laminate, form new daughter cell walls via eleutheroschisis, and have plastids with girdle lamellae and a ring-shaped genophore. The flagellar apparatus of Phaeothamnion zoospores (described in a previous study) is chosen as representative of the new class. The flagella are inserted laterally, basal bodies form an angle of ca. 145° or more, a multi-gyred flagellar transitional helix is present and tripartite flagellar hairs lack lateral filaments. Genera placed in the Phaeothamniophyceae are assigned to the orders Phaeothamniales and Pleurochloridellales, each with a single family.
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phylogenetic relationships of the raphidophyceae and Xanthophyceae as inferred from nucleotide sequences of the 18s ribosomal rna gene
American Journal of Botany, 1997Co-Authors: Daniel Potter, Gary W Saunders, Robert A AndersenAbstract:Some earlier studies suggested an evolutionary relationship between the Raphidophyceae (chloromonads) and Xantho- phyceae (yellow-green algae), whereas other studies suggested relationships with different algal classes or the Oomycete fungi. To evaluate the relationships, we determined the complete nucleotide sequences of the 18S ribosomal RNA gene from the raphidophytes Vacuolaria virescens, Chattonella subsalsa,and Heterosigma carterae,and the xanthophytes Vauch- eria bursata, Botrydium stoloniferum, Botrydiopsis intercedens,and Xanthonema debile. The results showed that the Xan- thophyceae were most closely related to the Phaeophyceae. A cladistic analysis of combined data sets (nucleotide sequences, ultrastructure, and pigments) suggested the Raphidophyceae are the sister taxon to the Phaeophyceae-Xanthophyceae clade, but the bootstrap value was low (40%). The raphidophyte genera were united with high (100%) bootstrap values, supporting a hypothesis based upon ultrastructural features that marine and freshwater raphidophytes form a monophyletic group. We examined the relationship between Vaucheria, a siphoneous xanthophyte alga, and the Oomycetes, and we confirmed that Vaucheria is a member of the class Xanthophyceae. Partial nucleotide sequences of the 18S rRNA gene from eight xantho- phytes (including Bumillariopsis filiformis, Heterococcus caespitiosus, and Mischococcus sphaerocephalus ) produce a phy- logeny that is not congruent with the current morphology-based classification scheme.
Enrico Massimiliano Negrisolo - One of the best experts on this subject based on the ideXlab platform.
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Phylogeny and Taxonomy of Xanthophyceae (Stramenopiles, Chromalveolata)
Protist, 2009Co-Authors: S. Maistro, Carlo Andreoli, Pa Broady, Enrico Massimiliano NegrisoloAbstract:The stramenopile class Xanthophyceae has been variously divided into two to seven orders. Previous molecular phylogenetic analyses of the class have had limited taxon/gene sampling or have focused on particular taxa. Despite these limitations para-polyphyletic groups have been identified at different taxonomic ranks. To investigate the phylogeny of the Xanthophyceae, a multiple alignment containing SSU rDNA, rbcL and psaA gene portions was analyzed according to bayesian inference, maximum likelihood, minimum evolution and maximum parsimony methods. This multigenic approach allowed robust resolution of evolutionary relationships within Xanthophyceae and the proposal of a taxonomic revision within the class. The best statistically supported tree either showed/or confirmed that several taxa at different taxonomic levels were para-polyphyletic. Ten epitypes were formally proposed for species of Chlorellidium, Botrydiopsis and Bumilleriopsis. Boundaries of these coccoid genera were redefined as monophyletic groups. Four major clades received strong statistical support. These accommodated most of the studied coccoid, filamentous and siphonous Xanthophyceae. Unicellular flagellates, amoeboid and palmelloid taxa were not included in the study. Botrydiopsis pyrenoidosa was excluded from Xanthophyceae and placed incertae sedis.
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Molecular phylogeny and evolution of the order Tribonematales (Heterokonta, Xanthophyceae) based on analysis of plastidial genes rbcL and psaA.
Molecular phylogenetics and evolution, 2007Co-Authors: S. Maistro, Paul A. Broady, Carlo Andreoli, Enrico Massimiliano NegrisoloAbstract:Tribonematales is an order of filamentous algae in the class Xanthophyceae (Heterokonta). Few molecular studies, all with a limited taxon sampling, have previously investigated its evolutionary history and phylogenetic relationships. We sequenced the chloroplast-encoded rbcL and psaA genes of several tribonematalean species and of several coccoid and siphonous forms that previous studies revealed to be strictly related to Tribonematales. Multiple alignments included mostly new sequences obtained from 42 taxa. Phylogenetic reconstructions were performed using the maximum likelihood method. The rbcL and psaA data sets were analyzed independently and combined in a single multiple alignment. Neither rbcL nor psaA genes showed intraspecific sequence variation. The former proved to be a better diagnostic marker than the latter for characterization of species. We explored effects produced on phylogenetic outcomes by selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on the combined data set. There is strong statistical support for trees that show several currently recognized taxonomic groups to be polyphyletic. The siphonous orders Botrydiales and Vaucheriales do not form a clade. Botrydiales and Tribonematales are polyphyletic as are the families Botrydiaceae, Centritractaceae and Tribonemataceae and the genera Xanthonema and Bumilleriopsis. We tentatively define new boundaries of the Tribonematales to include both coccoid and filamentous species having a bipartite cell wall and also the siphonous members of the genus Botrydium. Also, our results support morphological convergence at all taxonomic ranks in the evolution of the Xanthophyceae.
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Morphological convergence characterizes the evolution of Xanthophyceae (Heterokontophyta): evidence from nuclear SSU rDNA and plastidial rbcL genes.
Molecular phylogenetics and evolution, 2004Co-Authors: Enrico Massimiliano Negrisolo, S. Maistro, M. Incarbone, Isabella Moro, Luisa Dalla Valle, Paul A. Broady, Carlo AndreoliAbstract:Xanthophyceae are a group of heterokontophyte algae. Few molecular studies have investigated the evolutionary history and phylogenetic relationships of this class. We sequenced the nuclear-encoded SSU rDNA and chloroplast-encoded rbcL genes of several xanthophycean species from different orders, families, and genera. Neither SSU rDNA nor rbcL genes show intraspecific sequence variation and are good diagnostic markers for characterization of problematic species. New sequences, combined with those previously available, were used to create different multiple alignments. Analyses included sequences from 26 species of Xanthophyceae plus three Phaeothamniophyceae and two Phaeophyceae taxa used as outgroups. Phylogenetic analyses were performed according to Bayesian inference, maximum likelihood, and maximum parsimony methods. We explored effects produced on the phylogenetic outcomes by both taxon sampling as well as selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on a data set including both SSU rDNA and rbcL sequences. Trees obtained in this study show that several currently recognized xanthophycean taxa do not form monophyletic groups. The order Mischococcales is paraphyletic, while Tribonematales and Botrydiales are polyphyletic even if evidence for the second order is not conclusive. Botrydiales and Vaucheriales, both including siphonous taxa, do not form a clade. The families Botrydiopsidaceae, Botryochloridaceae, and Pleurochloridaceae as well as the genera Botrydiopsis and Chlorellidium are polyphyletic. The Centritractaceae and the genus Bumilleriopsis also appear to be polyphyletic but their monophyly cannot be completely rejected with current evidence. Our results support morphological convergence at any taxonomic rank in the evolution of the Xanthophyceae. Finally, our phylogenetic analyses exclude an origin of the Xanthophyceae from a Vaucheria-like ancestor and favor a single early origin of the coccoid cell form.
Carlo Andreoli - One of the best experts on this subject based on the ideXlab platform.
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Xanthophyceae
Handbook of the Protists, 2016Co-Authors: Silvia Maistro, Carlo Andreoli, Paul Broady, Enrico NegrisoloAbstract:The Xanthophyceae is a clade of stramenopilan photoautotrophs containing about\ud 118 genera and 600 species. Morphology ranges from free-living or attached\ud unicells to colonies and unbranched or branched filaments and siphons. A large\ud majority are found in freshwater and soil, while some occur in brackish and\ud marine habitats. Although abundant growth of a few species can occur in nature,\ud none are known to be of practical importance. They are characterized by possession\ud of chlorophylls a, c1, and c2 and a range of xanthophylls, but not fucoxanthin,\ud in generally yellowish-green, discoidal, parietal chloroplasts. Thylakoids are\ud in groups of three, and most species investigated have a single thylakoid forming\ud a girdle band around the periphery of the chloroplast. Chloroplasts are surrounded\ud by chloroplast endoplasmic reticulum. Pyrenoids, when present, are typically\ud semi-immersed and are not associated with granules of storage products. A cell\ud wall consisting of two overlapping parts occurs in some coccoid and filamentous\ud species. Reproduction is generally asexual but some, e.g., Vaucheria, exhibit\ud sexual reproduction. The taxonomic status of a significant number of species is\ud uncertain, especially those that are rarely observed, e.g., species of\ud Chloramoebales, Heterogloeales, and Rhizochloridales. Transfer of species to\ud the Eustigmatophyceae and other groups is likely. There is molecular phylogenetic\ud data for fewer than 20 % of species. Four major clades are recognized. Two\ud of these contain both coccoid and filamentous species. Many traditional orders,\ud families, and genera are paraphyletic or polyphyletic. It is presently convenient to\ud retain the traditional classification of seven orders based on morphology until\ud these difficulties are resolved following the inclusion of more species in phylogenetic\ud analyses
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Phylogeny and Taxonomy of Xanthophyceae (Stramenopiles, Chromalveolata)
Protist, 2009Co-Authors: S. Maistro, Carlo Andreoli, Pa Broady, Enrico Massimiliano NegrisoloAbstract:The stramenopile class Xanthophyceae has been variously divided into two to seven orders. Previous molecular phylogenetic analyses of the class have had limited taxon/gene sampling or have focused on particular taxa. Despite these limitations para-polyphyletic groups have been identified at different taxonomic ranks. To investigate the phylogeny of the Xanthophyceae, a multiple alignment containing SSU rDNA, rbcL and psaA gene portions was analyzed according to bayesian inference, maximum likelihood, minimum evolution and maximum parsimony methods. This multigenic approach allowed robust resolution of evolutionary relationships within Xanthophyceae and the proposal of a taxonomic revision within the class. The best statistically supported tree either showed/or confirmed that several taxa at different taxonomic levels were para-polyphyletic. Ten epitypes were formally proposed for species of Chlorellidium, Botrydiopsis and Bumilleriopsis. Boundaries of these coccoid genera were redefined as monophyletic groups. Four major clades received strong statistical support. These accommodated most of the studied coccoid, filamentous and siphonous Xanthophyceae. Unicellular flagellates, amoeboid and palmelloid taxa were not included in the study. Botrydiopsis pyrenoidosa was excluded from Xanthophyceae and placed incertae sedis.
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Molecular phylogeny and evolution of the order Tribonematales (Heterokonta, Xanthophyceae) based on analysis of plastidial genes rbcL and psaA.
Molecular phylogenetics and evolution, 2007Co-Authors: S. Maistro, Paul A. Broady, Carlo Andreoli, Enrico Massimiliano NegrisoloAbstract:Tribonematales is an order of filamentous algae in the class Xanthophyceae (Heterokonta). Few molecular studies, all with a limited taxon sampling, have previously investigated its evolutionary history and phylogenetic relationships. We sequenced the chloroplast-encoded rbcL and psaA genes of several tribonematalean species and of several coccoid and siphonous forms that previous studies revealed to be strictly related to Tribonematales. Multiple alignments included mostly new sequences obtained from 42 taxa. Phylogenetic reconstructions were performed using the maximum likelihood method. The rbcL and psaA data sets were analyzed independently and combined in a single multiple alignment. Neither rbcL nor psaA genes showed intraspecific sequence variation. The former proved to be a better diagnostic marker than the latter for characterization of species. We explored effects produced on phylogenetic outcomes by selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on the combined data set. There is strong statistical support for trees that show several currently recognized taxonomic groups to be polyphyletic. The siphonous orders Botrydiales and Vaucheriales do not form a clade. Botrydiales and Tribonematales are polyphyletic as are the families Botrydiaceae, Centritractaceae and Tribonemataceae and the genera Xanthonema and Bumilleriopsis. We tentatively define new boundaries of the Tribonematales to include both coccoid and filamentous species having a bipartite cell wall and also the siphonous members of the genus Botrydium. Also, our results support morphological convergence at all taxonomic ranks in the evolution of the Xanthophyceae.
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Morphological convergence characterizes the evolution of Xanthophyceae (Heterokontophyta): evidence from nuclear SSU rDNA and plastidial rbcL genes.
Molecular phylogenetics and evolution, 2004Co-Authors: Enrico Massimiliano Negrisolo, S. Maistro, M. Incarbone, Isabella Moro, Luisa Dalla Valle, Paul A. Broady, Carlo AndreoliAbstract:Xanthophyceae are a group of heterokontophyte algae. Few molecular studies have investigated the evolutionary history and phylogenetic relationships of this class. We sequenced the nuclear-encoded SSU rDNA and chloroplast-encoded rbcL genes of several xanthophycean species from different orders, families, and genera. Neither SSU rDNA nor rbcL genes show intraspecific sequence variation and are good diagnostic markers for characterization of problematic species. New sequences, combined with those previously available, were used to create different multiple alignments. Analyses included sequences from 26 species of Xanthophyceae plus three Phaeothamniophyceae and two Phaeophyceae taxa used as outgroups. Phylogenetic analyses were performed according to Bayesian inference, maximum likelihood, and maximum parsimony methods. We explored effects produced on the phylogenetic outcomes by both taxon sampling as well as selected genes. Congruent results were obtained from analyses performed on single gene multiple alignments as well as on a data set including both SSU rDNA and rbcL sequences. Trees obtained in this study show that several currently recognized xanthophycean taxa do not form monophyletic groups. The order Mischococcales is paraphyletic, while Tribonematales and Botrydiales are polyphyletic even if evidence for the second order is not conclusive. Botrydiales and Vaucheriales, both including siphonous taxa, do not form a clade. The families Botrydiopsidaceae, Botryochloridaceae, and Pleurochloridaceae as well as the genera Botrydiopsis and Chlorellidium are polyphyletic. The Centritractaceae and the genus Bumilleriopsis also appear to be polyphyletic but their monophyly cannot be completely rejected with current evidence. Our results support morphological convergence at any taxonomic rank in the evolution of the Xanthophyceae. Finally, our phylogenetic analyses exclude an origin of the Xanthophyceae from a Vaucheria-like ancestor and favor a single early origin of the coccoid cell form.
