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We describe three new Achnanthidium species, A. lacustre sp. nov., A. sublanceolatum sp. nov., and A. taipingensis sp. nov., from Taiping Lake, Anhui Province (China) based on light and scanning electron microscopy. A. lacustre sp. nov. belongs to the "A. minutissimum complex" of the genus, based on it having straight external distal raphe fissures and round to elliptical areolae. Both A. sublanceolatum sp. nov., and A. taipingensis sp. nov. belong to the "A. pyrenaicum complex" of the genus, based on them having transpically-elongated areolae and deflected external distal raphe fissures. All three species are sufficiently different from other similar species based on valve outline, shape of the axial and center areas, and striae density. These three new species are all observed in benthic collections from Taiping Lake.

Nupela major sp. nov., a new species of the diatom genus Nupela, is described from Maolan Nature Reserve, Guizhou Province, China. Observations were made using light and scanning electron microscopy documenting the size, shape and ultrastructure of the new species. Valves of the monoraphid frustules are elliptical-lanceolate with more or less cuneate, subtlety protracted ends. The raphe valve has a linear-lanceolate axial area and an irregularly-shaped central area. Striae appear intermittent or disrupted. The rapheless valve has a linear-lanceolate axial area widening in the center to form an asymmetrical central area that can in some specimens reach to the valve margin. The rapheless valve has a contoured valve face, with deep indentations in the axial area. The species is assigned to Nupela by virtue of its external occlusions on the areolae, and compared with similar species in the genus. The new species is found on stones beneath a waterfall and associated with a moss community.

Abstract: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.

Hantzschia species are uncommon in Xinjiang Province, usually found in small populations and found only in a few samples. However, the diversity in the region is relatively high, with 13 species and 1 variety being identified. Except for the cosmopolitan species H. amphioxys, H. abundans, H. virgata and H. distinctepunctata, most of the taxa in Hantzschia observed in this region have limited distributions, including H. vivacior, H. nitzschioides, H. compacta, H. barckhausenii, H. longa and H. vivax, as well as the species described herein as new. Four new species of Hantzschia are described: H. pseudobardii, H. sinensis, H. yili and H. subrobusta, a further two interesting species, H. vivacior and H. nitzschioides are documented with light and scanning electron microscopy. All species described are compared with other similar Hantzschia taxa from other localities or compared to holotype specimens. These data show a higher diversity of diatoms in Xinjiang Province than previously understood and provide additional information for understanding their biogeography.

Background and aims – We examine the possibility of the independent evolution of the same features multiple times across the pennate diatom tree of life. Methods and key results – Features we have studied include symmetry, raphe number and amphoroid symmetry. Phylogenetic analysis, with both morphological and molecular data suggest in each of these cases that the features evolved from 5 to 6 times independently. We also look at the possibility of certain features having evolved once and diagnosing large genera of diatoms, suggestive of an adaptive radiation in genera such as Mastogloia, Diploneis and Stauroneis. Conclusion – Formal phylogenetic analyses and recognition of monophyletic groups allow for the recognition of homoplasious or homologous features.

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Four new monoraphid diatoms are examined and described from a high-altitude (> 3000 m) region of western Sichuan, China.  The descriptions are based on light and scanning electron microscopy observations, and the four new species are compared with similar taxa worldwide.  Achnanthidium sichuanense sp. nov. has small, lanceolate-elliptical valves, with rounded apices. The outline and central area differentiate it from similar species.  The unique characteristic of Eucocconeis undulatum sp. nov. is that it has valves that are undulate along the apical axis, forming an “H”-shaped area on both raphe and rapheless valves as seen in light microscope (LM).  Platessa mugecuonesis sp. nov. and Platessa lanceolata sp. nov. are two small species, whose valve outlines and central areas make them different from other species in this genus.  A. sichuanense sp. nov. and E. undulatum sp. nov. are discussed in terms of the relationship between “Achnanthidium & Psammothidium” and “Eucocconeis & Psammothidium”, as these genera are difficult to separate according to morphological characteristics.