This article formally describes Craticula vanensis sp. nov., a new species of diatom from Lake Van, the largest soda lake in the world, and the fifth new species identified in the lake following an 81-years gap in investigations. A genomic approach based on short reads allowed the complete cluster of nuclear rRNA genes to be retrieved alongside the complete plastome, both later used in several single or multigene phylogenies, which surprisingly tended to associate C. vanensis to species of the genus Dorofeyukea. The complex structure of the mitogenome could only be resolved by long-read sequencing. It is characterized by its large size (116,698 bp), the presence of several introns in the cox1 gene, the use of an alternative genetic code with the putative reassignment of the UGA codon to arginine and the unexpected presence of six copies of the rRNA genes and nine copies of truncated nad2 sequences. A survey of published metabarcoding datasets suggested the presence of C. vanensis in a soda lake from Central Europe (Kakasszéki, Hungary), which was later confirmed by microscopy and suggests an extended distribution of this taxon.

Three species of the genus Achnanthidium K & uuml;tzing were found in a limnocrene spring (Sakarba & scedil;& imath;) in Eski & scedil;ehir, T & uuml;rkiye; they are documented and described based on light and scanning electron microscopy observations. The species A. jiuzhaiense and A. turkdoganiae sp. nov. belong to the general A. pyrenaicum complex, while A. levkovianum sp. nov. falls within the A. minutissimum complex. A. jiuzhaiense and A. turkdoganiae can be distinguished from A. pyrenaicum by valve apices, round and slightly drawn-out in A. pyrenaicum vs subcapitate to capitate in A. jiuzhaiense and rostrate in A. turkdoganiae. Achnanthidium jiuzhaiense has unique S-shaped hymenate pores connecting areolae along the striae. Achnanthidium levkovianum sp. nov. is distinguished from A. minutissimum by the long transapically elongated formation on the external valve and the evenly distributed striae on the valve. Valve outline, broadly linear-lanceolate with rounded valve apices in A. levkovianum are different from the linear-lanceolate with protracted, rostrate to subcapitate apices in A. minutissimum. The three species are compared to other related species: A. turkdoganiae to A. deflexum, A. druartii, A. linannulum, A. sublanceolatum and A. chitrakootense; and A. cf. convergens. The species are found in a unique spring environment with, alkaline waters of reasonable oxygen levels, pH 7.7-7.9 and high conductivity (545-575 & micro;S.cm-1).

This study introduces Halamphora witkowskii sp. nov., a newly discovered diatom species from Lake Van, the world's largest soda lake known for its high alkalinity. Detailed morphological and morphometric analyses using light and scanning electron microscopy effectively distinguished this new species from closely related taxa, including Halamphora minima, H. coffeaeformis, and H. tumida. Additionally, culturing studies from live cells led to the establishment of two separate monocultures, which were utilized for phylogenetic analysis using the rbcL molecular marker, further confirming the distinctiveness of Halamphora witkowskii from other known species.

A new Fallacia cinariana sp. nov. is described from a unique extreme microenvironment in the highly calcareous Kaklık Cave, Pamukkale Travertines in the Western Anatolian Karst Region, Türkiye with calcareous (pH 8.2) rich waters. Valves of F. cinariana are small (<15 um), linear to linear-elliptic with rounded ends. As with the type species for the genus (F. pygmaea (Kützing) Stickle & D.G.Mann), the axial area is composed of a narrow raphe sternum and valve face slits/occlusions on either side, 500–900 nm length. The striae are biseriate and form around a small round to elliptic central area. Falacia subhamulata Lange-Bertalot from Europe is considered the closest morphologically aligned species being larger, wider, broader central area, elliptic to round valve face slits/opening, and fewer biseriate striae. Other comparable taxa include Fallacia subhamulata (Grunow) D.G.Mann, F. angarae, Metzeltin, Kulikovskiy & Lange-Bertalot, F. helenensis (Schulz) D.G.Mann, F. lange-bertalotii Reichardt, F. lenzii Lange-Bertalot and F. pseudohelensis Kulikovskiy, Metzeltin & Lange-Bertalot. Among them, Fallacia lange-bertalotii (originally described from the Europe) co-occurs in Kaklik Cave and is similar, but F. cinariana has different morphological characters and distinct valve face slits/occlusions.

The current article introduces and describes Haslea berepwari sp. nov., a new species of diatom discovered in the vicinity of Boulouparis, New Caledonia. Under light microscopy, H. berepwari sp. nov. strongly resembles Haslea pseudostrearia, but preliminary molecular barcoding conducted using partial 18S and rbcL genes suggested that it was a distinct species. This was confirmed first by scanning electron microscopy which showed the differences in stria densities between both species. A short-reads genome-skimming protocol applied on H. berepwari sp. nov. led us to obtain its complete mitochondrial and plastid genomes. The mitogenome is 36,572 bp in length and as already observed among other species of Haslea spp., the nad6 and nad2 genes are fused within a single open-reading frame. The plastome is 131,897 bp length, and unlike the mitogenome, it is not colinear with those of H. pseudostrearia. The results derived from the sequencing of the plastome allowed to perform a 123-gene multigene maximum likelihood phylogeny that associates H. berepwari sp. nov. to H. pseudostrearia with maximum support at the nodes but also strictly distinguishes them, suggesting a greater genetic distance between these species than what has been previously observed between other marennine-producing species.

In this study, we describe Halamphora vantushpaensissp. nov., a newly identified diatom species found in the highly alkaline Lake Van in Eastern Turkey (Türkiye). This new species is characterized morphologically by light and scanning electron microscopy, performed on both wild and cultivated samples. Two monoclonal cultures were submitted to a genome-skimming approach, giving access to the complete sequence of their nuclear rRNA cluster of genes, mitochondrial and plastid genomes. Both strains were highly similar from the genomic point of view, with few mutations noted, although in organellar genomes some of them concerned protein coding genes and were non-silent. Also, the group II intron in the mitochondrial cox1 gene was found to display a relatively high number of polymorphisms. The plastome also distinguishes itself from other Halamphora spp. by the extension of its inverted repeat at the expense of the two single copy regions of the genome. Maximum likelihood molecular phylogeny inferred from a concatenated three genes dataset (18S, psbC and rbcL) positions this species within the K clade, which is known to contain hypersaline to freshwater species.

This paper describes a new species of Halamphora - Halamphora lombokensis sp. nov. and records for the first time Halamphora banzuensis for the coasts of Indonesia. The study utilized light and scanning electron microscopy to meticulously examine the morphology. These species were found at Kuta Beach on the island of Lombok in Indonesia in highly saline sandy environments. The newly identified species, H. lombokensis sp. nov., is characterized by its semi-lanceolate to narrowly semi-elliptic shape with a straight ventral and convex dorsal margin. The study contributes to our understanding of marine diatom flora in Indonesia's coastal regions.

The current article describes Navicula vanseeasp. nov., a new species of diatom from Lake Van, a highly alkaline lake in Eastern Anatolia (Türkiye). The description is based on light and scanning electron microscopy performed on two monoclonal cultures. The complete nuclear rRNA clusters and plastid genomes have been sequenced for these two strains and the complete mitogenome for one of them. The plastome of both strains shows the probable loss of a functional ycf35 gene. They also exhibit two IB4 group I introns in their rrl, each encoding for a putative LAGLIDADG homing endonuclease, with the first L1917 IB4 intron reported amongst diatoms. The Maximum Likelihood phylogeny inferred from a concatenated alignment of 18S, rbcL and psbC distinguishes N. vanseea sp. nov. from the morphologically similar species Navicula cincta and Navicula microdigitoradiata.

Ecological quality evaluations using diatoms, which are accepted as one of the biological quality components have accelerated recently in different basins of Türkiye. Asi Basin which has a small catchment area within the borders of Türkiye, located near to Syrian border and is under the influence of a Mediterranean climate. This study aims to determine the water quality of the streams in this basin by using various diatom indices and to determine the environmental pressures affecting the diatom community structure. In this study, 21 rivers of the Asi Basin were sampled three times during 2019 to evaluate their ecological status by using 18 different diatom indices. A total of 157 diatom taxa were recorded in these rivers. Different environmental variables were also sampled combined with diatoms, and according to RDA, alkalinity (ALK), electrical conductivity (EC), total phosphorus (TP), and total nitrogen (TN) were determined as the most decisive pressures for the distribution of diatom assemblages. In terms of TN, Bayrak River (R7), while in terms of TP, Üçocak River (R12) have II. class water quality. The eight diatom indices showed significant correlations with TP ( p < 0.01). The Trophic-Saprobic index (LOBO) showed the highest response to the TP (R 2 = 0.63) and was consistent with the indicator species. This index was also compatible with the evaluation results made according to the water quality classes of the sites. LOBO index classified these rivers as high-good or poor-bad effectively in terms of TP. It was the first time that the LOBO which was developed to evaluate the surface freshwaters of Brazil has a high correlation with TP in a basin of Türkiye.

Kaskar Mountains is located in the Eastern Black Sea Region in Turkiye. The mountain-ous area includes granite and volcanic rocks influencing water conditions. Mosar Lake is located at 40 & DEG;42'35" N and 40 & DEG;54'51" E in the Versenik Valley with an altitude of 3.060 m. a.s.l. The samples were collected in July 2015 from epilithic and epipelic substrata. Epilithic samples were collected using a toothbrush and epipelic samples collected using a pipette. The description of the new spe-cies Sellaphora lucectoriana sp. nov. were given in this study. Valve apices and striae density are diagnostic characters for S. lucectoriana. Sellaphora hentiensis (Kulikovskiy, Lange-Bertalot, A.Witkowski & Dorofeyuk) C.E.Wetzel & Ector and S. laticeps (Hustedt) C.E.Wetzel, Ector, Van de Vijver, Compere & D.G.Mann are similar in morphology and general outline. S. hentiensis is the most similar, however, S. lucectoriana has subcapitate apices and a higher striae density. S. laticeps has larger valves with abruptly protracted and broadly capitate apices.

The present study aimed to contribute to the algal flora of Türkiye by Bacillariophyta (diatom) as new records for the Turkish freshwater. Phytobenthos and phytoplankton were sampled three times (spring, summer, and autumn) a year between 2017 and 2019. Samples of the phytoplankton were collected with a water sampler from three depths, and samples of diatoms were obtained as epiphytic in the littoral zone of the lakes. However, if macrophytes were absent, epilithic or epipelic diatoms were sampled in lakes. Also, samples of phytobenthos were preferred as epilithic in rivers. However, if stones were absent, epiphytic or epipelic diatoms were sampled. During the studied period, a total of 895 diatom taxa were determined as planktonic (378 taxa) and benthic (860 taxa) in lakes and rivers of 25 river basins of Türkiye, and a total of 39 new records were identified. The highest diatom taxa were determined in the Fırat-Dicle, Konya, Antalya, and Büyük Menderes basins with 11, 11, 10, and 6 taxa, respectively. On the other hand, new records were not detected in 10 basins.

A new species Surirella caljoniana sp. nov. is described from a unique microenvironment in the mountainous region of Türkiye. The taxon was found in a small soda spring which is an important water source for the Kızılırmak River. Surirella caljoniana is similar to Surirella brebissonii Krammer & Lange-Bertalot, S. brebissonii var. kuetzingii Krammer and Lange-Bertalot, S. lacrimula J.D.English, S. neglecta Reichardt and S. subsalsa W.Smith in morphology and shape. Unlike the other taxa, S. caljoniana has an oval-elliptic, slightly heteropolar outline, larger length/width ratio and a narrowly rounded, slightly protracted foot pole. Over the striae, distinct fimbriate silica protrusions are evident and similar to some marine species within the Pinnatae.

Cold environments are considered extreme biomes and historically thought to be barren and unproductive. However, investigations show that some of the coldest regions in the world represent unique biodiversity hotspots. In this review, the prominent diatom communities of alpine lakes and ponds across different parts of the world, including the Arctic, Antarctic, and alpine regions, are evaluated. Glacial lakes in western Asia (Turkey) are specifically examined as a proxy for extreme cold aquatic systems between the primary mountainous areas of the Alps and the Himalaya. Biogeographically, Turkey is a subtropical region with two prominent glacial ecozones (southern Taurus and northeastern Anatolian Mountains). In this study, glacial lakes in the Kaçkar Mountains, northeastern Anatolia, are evaluated noting the importance of genera with smaller diatom taxa including Genkalia, Psammothidium, and Eunotia. The presence of genera like Genkalia and cold environment species like Psammothidium subatomoides highlight the isolation of alpine biomes in subtropical regions. Broad biogeographic distributions of biological diversity from polar to alpine are considered, and a number of taxa within Eunotia and Psammothidium are recorded for the first time in this region.

Aim of the study: The Gala Lake, which has a status of National Park and is an under-protection area, is the one of the most important natural stagnant water bodies in the Marmara Region of Türkiye. However, it is under effect of a significant agricultural stress sourced by mainly paddy cultivation. In this research, the epiphytic diatoms of Gala Lake were investigated, and the trophic status of the lake was assessed by applying the Biological Diatom Index (BDI). Material and methods: Epiphytic diatom samples were collected from the submerged macrophytes from 5 selected locations on the lake (G1–G5) with different ecological characters observed to be exposed to different pollution pressures. Results and conclusions: As a result of taxonomic data, 37 diatom species were recorded by identifying a total of 2095 valves, and Cyclotella meneghiniana, Bacillaria paxillifera, and Navicula recens were found as the most dominant species for the Gala Lake. According to the results of bioindication data, Gala Lake was found to be in a "eutrophic state"—"having poor water quality" in terms of applied BDI.

In order to detect the effects of different stressors on the littoral diatom assemblages and biodiversity of the lentic systems in two different basins in Türkiye, 15 lentic systems in the Akarçay and Asi basins were sampled three times (spring, summer, and fall) for littoral diatoms and environmental variables. The biological assessment of these sites was also evaluated using 9 different river and lake diatom indices. Based on the total phosphorus (TP), total nitrogen (TN), electrical conductivity (EC), salinity (SAL) values, and dominant diatom species, three lentic systems in Akarçay Basin (Lake Eber, 26 Ağustos Pond, and Lake Karamık) were more eutrophic and under the pressure of anthropogenic and climatic (precipitation) stressors. Trophic diatom index for lakes (TDIL) showed a higher correlation with TN and TP and was the most effective index in explaining ecological quality in 15 lentic systems. The species richness of diatoms was also negatively affected by EC and SAL values. The lentic systems of the two basins were separated from each other based on the species composition and the distribution of the dominant species with the effect of altitude (ALT). Considering the distribution of diatom assemblage of the lentic systems in these two basins, anthropogenic, climatic, and geographical factors have become prominent to shape the diatom community structure.

Craspedostauros E.J. Cox is a diatom genus comprising 17 taxa reported from various regions of the world. While many species of Craspedostauros are epibiontic, the taxa have variable ecological preferences. In this study we formally describe Craspedostaurosnazmiisp. nov., an epilithic species discovered along the Turkish Black Sea Coast, based on light and scanning electron microscopy. Craspedostaurosnazmiisp. nov. is characterized by valves that are lanceolate to narrowly lanceolate, slightly constricted near the apices with uniseriate, parallel throughout the whole valve, transapical striae and and the presence of an apical silica flap. The areolae are distributed over the valve face and the mantle. The differences and similarities between C.nazmiisp. nov. and established species of Craspedostauros are discussed. Based on shape and morphometrics, the most similar species is Craspedostauroscapensis, but it is easily distinguished from C.nazmiisp. nov. by its lack of an apical silica flap.

Lake Salda has a unique environment due to the presence of hydromagnesite stromatolites. Samples collected from the stromatolites contained a new diatom species, Gomphonella saldanensis sp. nov., which is described based on light and scanning electron microscopy. The main character of the taxon is its linear-lanceolate outline with a rostrate headpole and narrowly rounded footpole. The striae are strongly radiate mid-valve, becoming parallel to slightly radiate towards the poles. Elliptical Fourier and Linear Discriminant analyses indicate that there are different shape forms within the same taxon. Based on LM observations, G. saldanensis is similar to Gomphonema lagerheimii f. simplex, G. geisslerae, Gomphonella calcarea, G. olivacea, G. acsiae and G. coxiae. However, G. lagerheimii f. simplex differs with slightly radiate striae throughout the valve. Gomphonella geisslerae has a slightly undulate raphe and linear apices. Larger specimens of G. acsiae are lanceolate, clavate in smaller specimens. The remaining Gomphonella species, G. calcarea, G. coxiae and G. olivacea have broader outlines and lower stria densities.

Çanakkale is located in Western Anatolia, a region known for extensive mining in the country. In this study, three new species: Nitzschia arslaniana sp. nov., Nitzschia efeiana sp. nov., and Nitzschia szaboiana sp. nov. are described from highly acidic environments in Çanakkale. In morphology, Nitzschia arslaniana is similar to Nitzschia inconspicua but Nitzschia inconspicua is broader, with a lower fibulae density. Nitzschia efeiana is similar to Nitzschia. bremensis, Nitzschia capitellata, Nitzschia homburgiensis, Nitzschia hybrida, Nitzschia palustris, and Nitzschia pellucida. However, Nitzschia efeiana has variable fibulae widths, thickened virgae on its external valve face, and an elevated ridge on the valve margin opposite the keel. Nitzschia szaboiana is similar to Nitzschia pusilla, but the later taxon has a higher striae density. This study highlights the unique species diversity of extreme environments, including anthropogenic extreme environments, by describing three new taxa in the same genus.