Huan Zhu

Systematics of a Kleptoplastidal Dinoflagellate, Gymnodinium eucyaneum Hu (Dinophyceae), and Its Cryptomonad Endosymbiont

New specimens of the kleptoplastidal dinoflagellate Gymnodinium eucyaneum Hu were collected in China. We investigated the systematics of the dinoflagellate and the origin of its endosymbiont based on light morphology and phylogenetic analyses using multiple DNA sequences. Cells were dorsoventrally flattened with a sharply acute hypocone and a hemispherical epicone. The confusion between G. eucyaneum and G. acidotum Nygaard still needs to be resolved. We found that the hypocone was conspicuously larger than the epicone in most G. eucyaneum cells, which differed from G. acidotum, but there were a few cells whose hypocone and epicone were of nearly the same size. In addition, there was only one site difference in the partial nuclear LSU rDNA sequences of a sample from Japan given the name G. acidotum and G. eucyaneum in the present study, which suggest that G. eucyaneum may be a synonym of G. acidotum. Spectroscopic analyses and phylogenetic analyses based on nucleomorph SSU rDNA sequences and chloroplast 23 s rDNA sequences suggested that the endosymbiont of G. eucyaneum was derived from Chroomonas (Cryptophyta), and that it was most closely related to C. coerulea Skuja. Moreover, the newly reported kleptoplastidal dinoflagellates G. myriopyrenoides and G. eucyaneum in our study were very similar, and the taxonomy of kleptoplastidal dinoflagellates was discussed.

Massive Trentepohlia-bloom in a glacier valley of Mt. Gongga, China, and a new variety of Trentepohlia (Chlorophyta).

Trentepohlia is a genus of subaerial green algae which is widespread in tropical, subtropical, and also temperate regions with humid climates. For many years, small-scale Trentepohlia coverage had been found on the rocks of some glacier valleys on the northern slopes of Mt. Gongga, China. However, since 2005, in the Yajiageng river valley, most of the rocks are covered with deep red coloured algal carpets, which now form a spectacular sight and a tourist attraction known as ‘Red-Stone-Valley’. Based on morphology and molecular data, we have named this alga as a new variety: Trentepohlia jolithus var. yajiagengensis var. nov., it differs from the type variety in that its end cells of the main filament are often rhizoid, unilateral branches. This new variety only grows on the native rock, both global warming and human activity have provided massive areas of suitable substrata: the rocks surfaces of the Yajiageng river valley floodplain were re-exposed because of heavy debris flows in the summer of 2005; plus human activities such as tourism and road-building have also created a lot of exposed rock! In summer, the glaciers of the northern slopes of Mt. Gongga have brought to the valleys wet and foggy air, ideal for Trentepohlia growth. The cells of the new variety are rich in secondary carotenoids (astaxanthin?), which helps the algal cells resistance to strong ultraviolet radiation at high altitudes (they are only found on rock surfaces at alt. 1900–3900 m); the cells are also rich in oils, which gives them high resistance to cold dry winters.

Phylogenetic position of Jaoa, a green algal genus endemic to China

Jaoa prasina, a freshwater green alga endemic to China, was collected from a stream in Hubei province, China. Unialgal cultivation, morphological observation, and phylogenetic analyses of small subunit ribosomal DNA and RuBisCO large subunit sequences were performed. When cultured on agar medium, the alga was irregularly filamentous, similar to marine species of Acrochaete. Aplanospores were observed on solid medium. A vesicular‐like thallus without rhizoids developed in liquid medium, similar to specimen development in natural habitats. Molecular phylogenetic analyses revealed that Jaoa was closely related to the marine genera Acrochaete Pringsheim and Ulvella Crouan & Crouan. The results suggested the genus Jaoa is a member of the family Ulvellaceae (Ulvophyceae), which contains mostly marine algae. The family name Jaoaceae should be abandoned. We speculate that Jaoa may have evolved from a marine Ulvellaceae ancestor.

Morphological Examination and Phylogenetic Analyses of Phycopeltis spp. (Trentepohliales, Ulvophyceae) from Tropical China

During an investigation of Trentepohliales (Ulvophyceae) from tropical areas in China, four species of the genus Phycopeltis were identified: Phycopeltis aurea, P. epiphyton, P. flabellata and P. prostrata. The morphological characteristics of both young and adult thalli were observed and compared. Three species (P. flabellata, P. aurea and P. epiphyton) shared a symmetrical development with dichotomously branching vegetative cells during early stages; conversely, P. prostrata had dishevelled filaments with no dichotomously branching filaments and no symmetrical development. The adult thalli of the former three species shared common morphological characteristics, such as equally dichotomous filaments, absence of erect hair and gametangia formed in prostate vegetative filaments. Phylogenetic analyses based on SSU and ITS rDNA sequences showed that the three morphologically similar species were in a clade that was sister to a clade containing T. umbrina and T. abietina, thus confirming morphological monophyly. Conversely, Phycopeltis prostrata, a species with erect filaments, sessile gametangia on the basal erect hair, larger length/width ratio of vegetative cells and very loosely coalescent prostrate filaments, branched separately from the core Phycopeltis group and the T. umbrina and T. abietina clade. Based on morphological and molecular evidence, the genus Phycopeltis was paraphyletic. Furthermore, the traditional taxonomic criteria for Phycopeltis must be reassessed based on phylogeny using more species. A new circumscription of the Phycopeltis and the erection of new genera are recommended.

Morphology and phylogenetic position of Stomatochroon reniformis var. chinensis var. nov. (Trentepohliales, Ulvophyceae), a rare endobiotic alga from China

Abstract: Specimens of the genus Stomatochroon (Trentepohliales, Ulvophyceae) were found in leaf stomata of the fruit tree Syzygium samarangense (Myrtaceae). Phylogenetic analysis based on 18S rDNA sequences showed that Stomatochroon was closely related to Cephaleuros. The specimens were identified as Stomatochroon reniformis based on the branched internal filamentous and ovoid gametangia. However, our specimens differed from the type by having larger basal and clavate cells, a noticeable stalked gametangium, and secondary growth of the sporangiate-laterals. Consequently our taxon was described as a new variety, S. reniformis var. chinensis var. nov. We found no physiological dysfunction or host tissue hyperplasia was caused by the algal infection. The waterlogged and dead host tissue was probably caused by plugged host stomata that resulted from growth of this alga. This interpretation means this alga was an endophyte, not a parasite.

Three novel coccoid green algae within the Watanabea clade (Trebouxiophyceae, Chlorophyta) from China.

Coccoid green algae are extremely diverse despite their simple coccoid phenotype, a phenotype that may be the result of convergent evolution. In this study, we used a polyphasic approach combining molecular phylogenetic analyses, morphology and ultrastructure to investigate isolated coccoid strains from China, and our results reveal three new lineages of Trebouxiophyceae: the novel genus and species Mysteriochloris nanningensis gen. et sp. nov., and the two novel species Phyllosiphon coccidium sp. nov. and Desertella yichangensis sp. nov. (Trebouxiophyceae, Chlorophyta). We provide a detailed characterization of the novel microalgae which they are autosporic coccoid unicells and have parietal chloroplasts. In phylogenies based on 18S rDNA sequences and the chloroplast ribulose-bisphosphate carboxylase gene (rbcL), these three algae are nested within the Watanabea clade and are different from any known algae. M. nanningensis FACHB-1787 is not really close to any known algae within the Watanabea clade. Phyllosiphoncoccidium FACHB-2212 is within the Phyllosiphon lineages. D. yichangensis FACHB-1793 is closely related to Desertella californica and described as a representative of a novel species of the genus Desertella.

Jenufa lobulosa sp. nov. (Chlorophyceae, Chlorophyta), a new epilithic, terrestrial species described from China

Abstract: Unicellular coccoid green algae are characterised by a high cryptic diversity, but such diversity is still poorly known, especially in terrestrial environments. The genus Jenufa, first described in 2011 from terrestrial habitats, currently includes three species: J. perforata, J. minuta and J. aeroterrestrica. We describe a new species, Jenufa lobulosa sp. nov. The type strain FACHB-2128 was isolated from sandstone surfaces in Nanning, Guangxi Province, a subtropical area in southwestern China, and the cultured material was examined using light and electron microscopy. It shared representative features of the genus: a parietal perforated chloroplast with several lobes, no pyrenoids, and asexual reproduction via autospores. However, J. lobulosa differed from congeners in the mean size of its vegetative cells and autosporangia, the number of autospores and cell wall thickness. Phylogenetic analyses of 18S rDNA and rbcL sequences showed that strain FACHB-2128 belonged to the Jenufa clade of the Chlorophyceae, forming an independent lineage and differing from any known species. The position of strain FACHB-2128 within Jenufa was also supported by ITS2 rDNA sequences.

Morphology and molecular phylogeny of Trentepohliales (Chlorophyta) from China

Abstract The order Trentepohliales is composed of a complex of five aerial genera of branched filamentous green algae, Trentepohlia, Printzina, Phycopeltis, Cephaleuros and Stomatochroon; polyphyly has been discovered in some of these genera and species. To clarify the diversity and some taxonomic problems in the Trentepohliales, we collected specimens from southern China and successfully cultured the majority of them. We carefully observed morphological traits and performed phylogenetic analyses based on new 18S and ITS rDNA sequences obtained during the present study. Our results suggested that the ostiole position of the zoosporangia might effectively indicate the main lineages of Trentepohliales, with reassessment of the genera Trentepohlia and Printzina required based on this ostiole positioning. However, further molecular investigation, particularly for the genus Phycopeltis, is required. Phenotypic plasticity was very common in Trentepohlia and Cephaleuros and the traditionally circumscribed taxa may not be reliable. In Cephaleuros, the lichenized species do not form a single clade and most species are paraphyletic. Additionally, we suggest that a lack of description of the internal systems could be one reason for the difficulties in species identification. Further taxonomic studies should focus on an emendation of Cephaleuros and elucidating the molecular diversity of Phycopeltis.

Molecular phylogeny and morphological diversity of inland Cladophora (Cladophorales, Ulvophyceae) from China

Abstract: Cladophora has a global distribution and provides a habitat and food for numerous organisms. However, the taxonomy of Cladophora is confusing and poorly defined. In this study, 69 freshwater and brackish-water Cladophora samples from inland China were collected, and both morphological and phylogenetic analyses of these samples were performed. The concatenated molecular phylogenies based on ribosomal DNA sequences showed that these inland samples belonged to two groups: freshwater Cladophora and non-freshwater Cladophora. The phylogenetic results showed that there were eight clades in the freshwater group. The results of morphological observation showed characteristic similarities among the clades, and the samples in each clade exhibited different degrees of phenotypic plasticity. The prediction model for internal transcribed spacer 2 secondary structure showed that freshwater Cladophora contain one ring structure with three main helices (helices I–III), in which the helix III-2 region was most variable. The high phenotypic plasticity and lack of diagnostic characteristics of the freshwater Cladophora group made delineating species difficult and challenging. Further sampling from a broader range in combination with more efficient molecular markers are necessary to clarify the taxonomy of Cladophora in the future.

Improving phylogenetic inference of core Chlorophyta using chloroplast sequences with strong phylogenetic signals and heterogeneous models

Phylogenetic relationships within the green algal phylum Chlorophyta have proven difficult to resolve. The core Chlorophyta include Chlorophyceae, Ulvophyceae, Trebouxiophyceae, Pedinophyceae and Chlorodendrophyceae, but the relationships among these classes remain unresolved and the monophyly of Ulvophyceae and Trebouxiophyceae are highly controversial. We analyzed a dataset of 101 green algal species and 73 protein-coding genes sampled from complete and partial chloroplast genomes, including six newly sequenced ulvophyte genomes (Blidingia minima NIES-1837, Ulothrix zonata, Halochlorococcum sp. NIES-1838, Scotinosphaera sp. NIES-154, Caulerpa brownii and Cephaleuros sp. HZ-2017). We applied the Tree Certainty (TC) score to quantify the level of incongruence between phylogenetic trees in chloroplast genomic datasets, and show that the conflicting phylogenetic trees of core Chlorophyta stem from the most GC-heterogeneous sites. With removing the most GC-heterogeneous sites, our chloroplast phylogenomic analyses using heterogeneous models consistently support monophyly of the Chlorophyceae and of the Trebouxiophyceae, but the Ulvophyceae was resolved as polyphyletic. Our analytical framework provides an efficient approach to reconstruct the optimal phylogenetic relationships by minimizing conflicting signals.