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Recent research of the plankton and the surface sediments from Ribeirão do Campo reservoir (São Paulo, southeast Brazil) led to identification of two new cymbelloid diatom species: Encyonema acquasedis sp. nov. and Kurtkrammeria salesopolensis sp. nov. Their morphology was studied under both light and scanning electron microscopes aiming at describing the two species in detail. The morphology of each species is compared and discussed with morphologically similar taxa. The new species are different from all others in the Cymbellales due to a combination of characteristics including valve outline, striae, areolae structure, and raphe system. Both species were collected from an oligotrophic environment with both low pH and conductivity.

The type material of Cymbella schubartii was studied in order to clarify the differences and similarities within the complex of Encyonopsis species observed in southeastern Brazilian water bodies. Detailed examination using light and scanning electron microscopy of modern populations led us to propose two new Encyonopsis species, which are here described in details. Morphometric analysis of the valve shape supported the separation of four species: Encyonopsis schubartii, E. difficilis, E. sanctipaulensis, sp. nov. and E. linensis, sp. nov. Additionally, Cymbella perpusilla var. moreirae is formally transferred to the genus Encyonopsis. Regarding their ecological preferences, these species were found in rivers and reservoirs, especially in oligotrophic and oligo-mesotrophic environments.

Aim Relationships between species composition and variation patterns in diatom assemblages over six tropical reservoirs located in Southeast Brazil were explored. Methods Surface-sediment and phytoplankton diatom assemblages were determined and Canonical Correspondence Analysis was used to verify the set of environmental variables that best explain the species composition variation among sites. Results A total of 28 diatom taxa representing 20 genera were identified using light and scanning electron microscopy. Information on their ecological preferences was also provided. Humidophila biscutella is reported for the first time in Brazil whereas Sellaphora sassiana and Humidophila brekkaensis are reported for the first time in São Paulo State. Three groups of potential water quality indicators were delineated: the first suggests oligotrophic conditions, the second is related to cold waters with low luminosity in a mixing regime, and the third is a small group of tolerant species occurring in water with high conductivity, pH and total phosphorus conditions. Conclusion present study provided the first insight into the general diatom communities over six tropical reservoirs in Southeast Brazil and provided information on their ecology and distribution aiming bioassessment. The potential of water quality indicator diatom groups here outlined are in line with those reported in the literature and reinforce the importance of PEJU for the maintenance of ecological quality of reservoirs and reference conditions for the Metropolitan Region of São Paulo water sources.

In the present study, distance decay was used as a descriptor of the compositional variation in diatom communities’ similarity between different habitats (phytoplankton and surface sediment) and seasons (summer and winter; only for phytoplankton) along a geographical gradient of ~64km over six reservoirs located in south-east Brazil. Whether rates of decay in similarity changed with distance in tropical biological communities was tested, and the degree to which dispersal (geographic distance) and niche (habitat association) processes explain variation in the diatom communities was estimated. In addition, whether the diatom assemblage captured in the surface sediment reflected the water column assemblage events was evaluated. Distance–decay curves were estimated using linear regressions. Partial Mantel tests were performed to examine the significance of relationships among the biological, environmental and spatial datasets. Similarity decreased significantly with distance between habitats and seasons, but the results were not statistically significant for surface sediment assemblages. All diatom communities were controlled more by limited dispersal than by environmental factors, probably as a result of the water quality and scale of the study area.

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-(Cryptogams of the Parque Estadual das Fontes do Ipiranga, São Paulo, SP. Algae 36: Bacillariophyceae (Cymbellales)).The floristic survey of Cymbellales order (Bacillariophyceae) from the Parque Estadual das Fontes do Ipiranga (PEFI), São Paulo State, Brazil, is presented based on the analysis of 28 sampling units. Plankton samples were gathered with a plankton net and periphyton samples through collection and removal of diatoms attached to the stems of submerged plants. The samples were oxidized and analyzed under a light and a scanning electron microscope. Six genera and a total of 36 taxa were identified. Morphological characteristics and dimensions of the frustules were provided for all recorded taxa.Among the species identified, the following 13 are new records for the PEFI:

Resumo: Este trabalho é parte do estudo sobre as diatomáceas perifíticas presentes no rio das Pedras, Guarapuava, no estado do Paraná, Brasil, e resultou na identifi cação de 35 táxons infragenéricos, distribuídos em 12 gêneros e seis famílias. Foram considerados táxons constantes: Frustulia saxonica Rabenhorst, Gomphonema gracile Ehrenberg e Gomphonema parvulum (Kützing) Kützing. A análise da comunidade diatomológica forneceu informações das condições ecológicas, sendo que a predominância de espécies eutrófi cas revela águas ricas em substâncias nutritivas, indicando que o sistema encontrase alterado devido ao efeito causado por início de degradação de compostos orgânicos lançados no corpo d'água.Palavras-chave: Bacillariophyceae. Diatomáceas. Perifíton. Rio das Pedras.