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In our recent investigations of diatom diversity, we studied three species, namely, Skeletonema costatum, Skeletonema subsalsum, and Skeletonema potamos. Although they have been found frequently in Changjiang (Yangtze) River Basin, their morphological and molecular identification is difficult in taxonomy. Therefore, to integrate morphological and molecular biological approaches, we compared systematically their morphological characters and performed phylogenetic analysis. Twelve strains of Skeletonema were collected and isolated from Shanghai and Jiangsu, China, and their morphological characteristics were examined by light microscopy (LM) and the scanning electron microscopy (SEM). Based on morphological comparison, we determined that S. potamos is easy to distinguish from the other two species. The heavily silicified areolae, undulated or cleft distal ends of terminal fultoportula processes (TFPPs), absence of basal pores of fultoportula processes (FPPs), the root-like protrusions of FPPs, and no interlocking connection are the stable characteristics that can be used to identify S. potamos. However, there are only two features that can distinguish S. costatum from S. subsalsum, namely the location of terminal rimoportulae (TRPs) and the distal shape of TFPPs. In addition, we amplified and sequenced nine common genetic markers from the strains, from which 101 sequences were obtained, constructed phylogenetic trees based on the nine genes and evaluated that seven genes can be used to identify S. potamos, and revealed that S. subsalsum is the closest known relative of S. costatum, and only ATP synthetase beta-subunit gene (atpB) is able to distinguish them from each other, which strongly support that it is an effective molecular marker for Skeletonema. This work provided a theoretical basis for the taxonomic study of Skeletonema. [ABSTRACT FROM AUTHOR]

Melosira is one of the most common diatom genera found in freshwater ecosystems. There are many freshwater species of Melosira, of which M. varians is the most common. In our investigation of periphytic diatoms in the Jinsha River, China, a new species, M. capsularum sp. nov, was characterized in combined morphological and molecular approaches. M. varians was also analyzed using molecular data. The new species is similar to M. varians, M. moniliformis, M. nummuloides, and M. lineata in morphology. The cells are capsular and join to filaments by mucilage pads that are secreted on the valve face and united into pairs by their cingula. The valve face is domed and covered with small granules, and the valve mantle edge has a milled appearance. The two strains of M. capsularum are in a single clade obviously away from other Melosira species, as determined in phylogenetic analysis based on nuclear small subunit (SSU) rDNA sequences and the chloroplast-encoded rbcL gene. Thus, the results of morphological comparisons and phylogenetic analysis based on molecular data provide strong evidence that M. capsularum is a new species, thereby increasing the total number of recognized freshwater diatom species in China. In addition, we have systematically reclassified the freshwater Melosira that have been recorded in China. [ABSTRACT FROM AUTHOR]

Three new species of Hannaea Patrick from the Hengduan Mountains in China are formally described herein, based on light and scanning electron microscope observations. Hannaea yalaensis sp. nov. has three continuous inflations along the ventral margin, resulting in an undulate outline compared to the outline of the most commonly reported Hannaea species. The valve of Hannaea hengduanensis sp. nov. is narrower, asymmetrical about the apical axis with capitate apices, dorsal and ventral sides almost parallel. On the ventral side of valve is an unornamented central area. The valve of Hannaea clavata sp. nov. is clavate. Valve margin is straight or slightly curved. The apices of the valve constrict sharply to form the capitate ends. In addition, we also briefly described other Hannaea from this region. Here, we document the morphologies of these new species and discuss the biogeographic distribution of the genus Hannaea in Asia. [ABSTRACT FROM AUTHOR]

SUMMARY: Achnanthes maolanensis nov. sp. is a large diatom collected from subaerial, freshwater habitats in karst landforms in central‐south China. Living cells have two chloroplasts. Valves of this new species are panduriform in outline, slightly constricted in the middle part of the margins, with uniseriate areolae; the raphe is filiform, and there is a linear, thickened stauros in the central area of the RV. On the ARV, there is no central area, and as well there are no terminal orbiculi, marginal ridge, or terminal spine externally. The axial area (rapheless sternum) is located down the center, not offset from the center as in many other species of the genus and is narrow and almost straight. This suite of characters makes the new species easy to distinguish from other species in the genus. Its presence adds further documentation of the unique and diverse freshwater diatom flora from karst habitats in this region of China. [ABSTRACT FROM AUTHOR]

A new species,Simonsenia maolanianasp. nov., is reported from a typical karst landform, Maolan Nature Reserve, Guizhou Province, China. The valves are lanceolate (larger frustules) to elliptical-lanceolate (smaller frustules), widest in the centre of the valve, and narrowly rostrate, not protracted at the ends. The more lanceolate valve outline, greater valve width and coarser structure distinguishS. maolanianafrom otherSimonseniaspecies. A direct comparison between the new species and the sympatric (though rare)S. delogneiwas possible because the two occurred together at Maolan. This is the first report ofSimonseniafrom continental China. [ABSTRACT FROM AUTHOR]

Periphytic diatoms play important functional roles in aquatic ecosystems. Their community compositions are widely used in water quality monitoring due to their wide distribution, short reproductive cycles, and sensitivity to environmental changes. In this study, 116 samples of periphytic diatom samples were collected from lakes in the lower reaches of the Yangtze River. The weighted average without tolerance down-weighting regression method was used to develop total phosphorus (r2 = 0.661), total nitrogen (r2 = 0.699), and chemical oxygen demand (r2 = 0.423) models, and the optimal and tolerance values of 78 periphytic species were calculated. Then, a new index, the comprehensive diatom index (CDI), was established on the basis of the optima and tolerances of these 78 species concerning the three environmental variables (TP, TN, and COD) to assess the water trophic status of the lakes in this region. According to the CDI, the trophic statuses of 8, 17, 23, 30, 22, and 14 sample sites were oligotrophic, mesotrophic, light eutrophication, moderate eutrophication, heavy eutrophication, and ultra-eutrophication, respectively. The CDI was more strongly correlated with the conductivity, pH, TP, TN, COD, and TDS than other diatom indices. These results demonstrate that the CDI is a useful metric for assessing the water trophic status of the lakes in the lower reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

Benthic diatoms are an indispensable link of the water ecological system in terms of energy flow and material cycling, and they directly or indirectly reflect the status of the water environment. We sampled benthic diatoms and environmental factors from April to May of 2013 from 53 sites along the Ying River to study their application in local water trophic status assessment, with a focus on the dominant benthic diatom species, their composition and distribution pattern, and the relationship between benthic diatoms and environmental factors. A total of 370 species and varieties were identified, belonging to 56 genera and six orders. The dominant species were as follows: Nitzschia inconspicua Grunow, Achnanthidium minutissimum (Kützing) Czarnecki, Navicula aitchelbee L. L. Bahls, Nitzschia palea (Kützing) Smith, Cyclotella meneghiniana Kützing, Navicula submuralis Hustedt and Mayamaea atomus (Kützing) Lange-Bertalot. The Ying River was divided into five orders using the Strahler method and three regions according to total nitrogen, total phosphorus and ammonia nitrogen. In region Y-1, which had the lowest nutrient level, the dominant species was Achnanthidium minutissimum. In region Y-2, which had the highest nutrient level, Navicula aitchelbee, Nitzschia palea, and Cyclotella meneghiniana were dominant, while in region Y-3, which had moderate nutrient levels, Nitzschia inconspicua was dominant. Pearson’s correlation analysis and canonical correspondence analysis (CCA) revealed a significant correlation between the environmental factors with dominant species and diatom indices (especially the SPI). Our study indicates that dominant species and diatom indices can, to some extent, indicate the environment, especially nutrient distribution. [ABSTRACT FROM AUTHOR]