Achnanthidium Species Research Articles

Molecular Investigation of the Achnanthidium minutissimum Complex (Bacillariophyceae) from the Transbaikal Region with the Description of Three New Species

Representatives of the Achnanthidium minutissimum complex have been studied from the Transbaikal region, Russia. The Transbaikal region is known for its unique algal flora and high levels of endemism. Despite the group of monoraphid diatoms being studied quite extensively in this region in recent years, only four species of Achnanthidium have been reported so far. Three new species are described based on LM and SEM microphotographs and molecular data: Achnanthidium baicalonanum sp. nov., A. obscurum sp. nov. and A. angustum sp. nov. Comparison with similar species is given. The new species differ from other species of the genus by valve shape, striae and areolae structure, shape of external distal raphe ends and central area. According to molecular data, the new species form separate branches within the A. minutissimum complex. Ecological preferences of the new species are examined. All of the new species are only known from the Transbaikal region. This study contributes to the understanding of Achnanthidium taxonomy and biogeography and will be an asset to future biomonitoring studies.

Taxonomy and ecology of Achnanthidium (Bacillariophyta, Achnanthidiaceae) from southeastern Brazil with the description of six new species

The present study aims to expand the knowledge on Achnanthidium species occurring in tropical areas of southern Brazil. For this purpose, 345 samples from 179 sampling sites distributed throughout the state of São Paulo were analyzed for ‘monoraphid’ diatom diversity. This paper focuses on samples with a high abundance of Achnanthidium species. The permanent slides and stubs were observed using light and scanning electron microscopy. Morphometric analysis was performed to discriminate between similar species through the Elliptical Fourier Descriptors analysis. For this, valve outlines from Brazilian species were compared to those from type material available from the literature. The ecological optimum and tolerance was calculated for taxa that presented more than 10 % of occurrence per habitat. In total, 12 Achnanthidium species were observed. Six are described as new: Achnanthidium acutum sp. nov., A. brasiliense sp. nov., A. parvicapitatum sp. nov., A. paulistanum sp. nov., A. ritae sp. nov. and A. vandevijveri sp. nov. The morphometric analysis supported the differentiation between some taxa. Nine species, with occurrences of at least 10 % per habitat, had their ecological optimum and tolerance calculated. In general, these species prefer slightly acidic to neutral pH, medium electrolyte cond. and mesotrophic water conditions.

A new freshwater species Achnanthidiumkangdingnese (Bacillariophyta, Achnanthidiaceae) from Sichuan Province, China.

A new freshwater diatom species, Achnanthidiumkangdingnese Yu, You & Wang, sp. nov. from Sichuan Province, China, is described. The morphology of this species was analyzed with scanning electron microscopy (SEM) and light microscopy (LM). A.kangdingnese belongs to the A.initium-like subgroup, which has external distal raphe ends curved in opposite directions of the valve. The main characteristics of A.kangdingnese are its linear shape, rounded apices and transpically-elongated areolae on the both valves. The central area is well defined with one or two spaced striae of the raphe valve. And on the internal valve, areolae are occluded by hymens perforated by delicate slits, and each hymen is closely joined with the adjacent hymen. We compared the new species with other similar species of Achnanthidium, A.kangdingnese is considered to be sufficiently different from other similar species based on valve outline, shape of the axial and center areas, and striae density. The new species is known only from its type locality, a mountain lake in Kangding County.

Three new Achnanthidium (Bacillariophyceae) species from Lake Salda (Anatolia, Turkey), a deep soda lake

Background and aims – Kützing separated the genus Achnanthidium from the genus Achnanthes based on two species: Achnanthes minutissima and Achnanthidium microcephalum. These two genera were distinguished by the presence of stalks in the Achnanthes genus and their absence in Achnanthidium. Before electron microscopy, the difference between Achnanthes and Achnanthidium was not clear, especially in Achnanthidium minustissimum sensu lato. The aim of the study is to describe three new species of Achnanthidium from Lake Salda. Material and methods – Lake Salda is located in southwestern Anatolia, in Turkey. The diatoms were collected seasonally from four stations in the lake between 2016 and 2020, from different substrata (epipelic, epiphytic, and epilithic). Key results – Three new species belonging to the genus Achnanthidium have been found in Lake Salda, Turkey. Based on the morphological observations, all new taxa are part of the Achnanthidium minutissimum complex. Achnanthidium barlasii sp. nov. and A. dumlupinarii sp. nov. show a high degree of similarity to each other, but can be separated based on valve outline and a denser areolation, especially in striae close to the apices of the raphe valve. Both species can be distinguished from A. minutissimum based on more separate apices and less elliptic valves. In the case of A. dumlupinarii sp. nov., large specimens show slight undulations of the valve, which is a unique feature. Achnanthidium anatolicum sp. nov. is the most characteristic based on its valve width, broadly rounded valve apices, and almost straight valves in girdle view. All newly described Achnanthidium species can be found in lentic environments, with alkaline water and high calcium ion content. Conclusion – The newly described taxa occurred in the unique habitat of a soda lake. The environment of the lake is highly alkaline, rich in magnesium and calcium, and derived from limestone and dolomitic limestone rocks.

One new species of Achnanthidium Kützing (Bacillariophyta, Achnanthidiaceae) from Tibet, China

Tibet is a very important biodiversity hot spot in China and the diatom flora of this region has drawn a lot of attention. Diatom samples were collected from several places across Tibet. During research on the biodiversity of diatoms from Tibet, one Achnanthidium species showed unique features compared with other known taxa. It has linear-lanceolate valves with rounded apices, tear-drop shaped proximal raphe ends and ?-shaped distal raphe ends. The most distinctive character of this species, however, is the shape of areolae; since this species has nearly round external areolar openings on the valve face but more typical slit-like areolae present on the mantle. Here we describe it as new to science as Achnanthidium tibeticum Y. Liu & Kociolek. We compare this new species with other, similar taxa within the genus.

Two new freshwater species of the genus Achnanthidium (Bacillariophyta, Achnanthidiaceae) from Qingxi River, China.

We describe two new Achnanthidium species, A.anhuensesp. nov. and A.qingxiensesp. nov., from Qingxi River, Anhui Province, China, based on light and scanning electron microscopy. Both species belong to the “A.pyrenaicum complex” of the Achnanthidium genus, based on their possession of transapically-elongated areolae and deflected external distal raphe fissures. A.anhuensesp. nov. has a slightly irregular linear-lanceolate valve with rounded or weakly protracted apices and a transapically rectangular or bow tie central area on the raphe valve. A.qingxiensesp. nov. has a linear-lanceolate valve with rounded apices and the axial area distinct expanded apices on the rapheless valve. Both species differ sufficiently from other similar species, based on valve outline, shape of the axial and central areas and striae density. These new species were all collected from stone substratum.

Overwhelming role of hydrology-related variables and river types in driving diatom species distribution and community assemblage in streams in Cyprus

Mediterranean streams are naturally highly-stressed environments mainly due to wide seasonal and inter-annual fluctuations in water quantity. This natural pressure will be exacerbated by climate change and is a significant challenge when establishing efficient assessment methods. We studied environmental parameters (hydromorphology, hydrology, physical and chemical variables) and analysed 171 diatom samples from 65 stations in Cyprus (south-western part). Analyses revealed 290 taxa (273 identified to the species -or intraspecific- level) belonging to 65 genera. Even a tentative application of a Red-List approach underlined the overwhelming importance of hydrology-related variables and river types in determining species distribution and community ecological attributes in the water-stressed island of Cyprus. Somewhat unexpectedly, both species from threat categories of the diatom Red List for Central Europe (2018) and species one might predict would be included in such categories in a possible future Red List tailored for Cyprus occurred more frequently and were more relevant in assemblages from sites in intermittent streams. We found a majority of motile, medium- to small-sized, diatom species, including a small number of colony-forming species. We found several species known to be effective first colonizers (pioneer species) and, among these, there was a striking preponderance (80%) of Achnanthidium species, often with several species co-occurring, particularly at reference sites. A four-factor PERMANOVA found that all type (essentially hydrology-related) variables were significant, and there was also a significant effect of season. Agglomerative hierarchical cluster analysis revealed three end-groups, with groups being separated on ecohydro(geo)logical grounds (lentic/lotic), sediment grain size, discharge and pH. The reference sites were analysed in more detail to identify environmental determinants. 28% of the variation in diatom assemblage composition was explained by the measured variables, with those associated with stream type and hydrology explaining the greatest proportions (12 and 10%, respectively) whilst season accounted for the remainder. Our study emphasised a need for detailed investigations of ecological and distributional (including Red List status) traits of diatom species, and to acknowledge the importance of the hydrological peculiarities of Mediterranean streams, in particular the dramatic seasonal variability, when developing ecological assessment protocols for the region.

Three new subaerial Achnanthidium (Bacillariophyta) species from a karst landform in the Guizhou Province, China

Three new subaerial species of Achnanthidium are examined and described from a karst landform of central-south China based on light and scanning electron microscopy observations, and are compared with similar taxa worldwide. A. mediolanceolatum sp. nov. is elliptical-lanceolate, not linear-lanceolate as is more typical in this genus, as well as having a bow-tie shaped central area on the raphe valve and a large lanceolate axial area on the rapheless valve, features which together make it easy to distinguish this species from others. A. parvulum sp. nov. and A. guizhouensis sp. nov. are linear-elliptical in shape, which is more common for Achnanthidium and they differ from other species mainly in size, raphe, density of striae and shape of the central area. We compared these three new species with morphologically-similar taxa, and present their ecological settings and distributions as well. The relationship between Achnanthidium and Psammothidium is discussed, and the data from these new species from Guizhou presented herein suggest the two genera are difficult to separate.

Investigations of the type materials of Achnanthes parallela J.R.Carter and Achnanthes petersenii Hustedt (Bacillariophyceae) with comments on the genus Rossithidium Round & Bukhtiyarova

ABSTRACTAchnanthes parallela J.R.Carter was described from Lindean, Scotland, a freshwater species widely distributed in lochs of the southern Scottish uplands. It is currently regarded as a synonym of Achnanthes petersenii Hustedt first described from Svalbard. Investigation of type material for both taxa using light and scanning electron microscopy revealed that they are distinct species, and they can be distinguished using light microscopy alone. Current records of A. petersenii suggest a wider distribution in North America, Europe and Russia, but Achnanthes parallela and A. petersenii have not been distinguished in the past hence some records might require corrections. Based on our own observations, current discussions and a literature review, it is concluded that the two genera Rossithidium Round & Bukhtiyarova 1996 and Achnanthidium Kützing 1844 cannot yet be unambiguously defined on the basis of morphological criteria (discriminating characteristics) and there is insufficient molecular evidence to either support or reject the separation of these genera. On the basis of valve morphology and the match of characters with those in other species of Achnanthidium we propose the following combinations: Achnanthidium parallelum J.R.Carter ex Jüttner, D.M.Williams, Ector & C.E.Wetzel, sp. nov. and Achnanthidium petersenii (Hustedt) C.E.Wetzel, Ector, D.M.Williams & Jüttner, comb. nov.

Analysis of the type material of Achnanthes minutissima var. macrocephala (Bacillariophyta) and description of two new small capitate Achnanthidium species from Europe and the Himalaya

Background and aims – Two unknown benthic diatom species belonging to the genus Achnanthidium Kütz., and found in French and Nepalese freshwater habitats, were investigated. Both species are here described as new and compared with the original material of Achnanthes minutissima var. macrocephala Hust. [≡ Achnanthidium macrocephalum (Hust.) Round & Bukht.] from Indonesia.
 Methods – The morphology of three small and capitate Achnanthidium species was investigated using light microscopy (LM) and scanning electron microscopy (SEM).
 Key results – Achnanthidium coxianum sp. nov. (from the Himalaya) belongs to the group of species with hooked terminal raphe endings, while Achnanthidium peetersianum sp. nov. (from France) has variable terminal raphe endings which are usually slightly bent. Achnanthidium macrocephalum is a much rarer species and illustrations concerning its identity in the literature do not conform to the type studied here.
 Conclusions – The three species are similar in LM but clearly distinct in SEM. The shape of the areolae and terminal raphe endings separate the species. Achnanthidium macrocephalum has often been misidentified in studies from many areas of the world. It is similar to the new species in valve outline and in its small dimensions.

Three new freshwater species of the genus Achnanthidium (Bacillariophyta, Achnanthidiaceae) from Taiping Lake, China

We describe three new Achnanthidium species, lacustre sp. nov., sublanceolatum sp. nov., and taipingensis sp. nov., from Taiping Lake, Anhui Province (China) based on light and scanning electron microscopy. 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 sublanceolatum sp. nov., and 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.

Type analysis of Achnanthidium minutissimum and A. catenatum and description of A. tropicocatenatum sp. nov. (Bacillariophyta), a common species in Brazilian reservoirs

Background and aims – A commonly occurring Achnanthidium species has been observed in Brazilian reservoirs. The morphological features were described based on light and scanning electron microscope observations and it is described here as A. tropicocatenatum sp. nov.Methods – The new species was compared with the type material of morphologically similar taxa: Achnanthidium catenatum and A. minutissimum. Comparisons with the most related species based on literature were also provided. Traditional weighted-averaging approaches (WA) were applied to model ecological optima.Key results – Morphometric analysis of the valve shape supported the taxa separation; they can be easily differentiated by the morphological and ultrastructural features, including subcapitate to capitate apices, strongly radiate striae and a prominent axial area. This new species has been found in alkaline waters with low electrolyte content.Conclusions – Records of A. catenatum in Brazil are considered questionable because the species may have been confused with A. tropicocatenatum sp. nov.

Multifunctional methacrylate-based coatings for glass and metal surfaces

In order to prevent freshwater biofouling glass and metal surfaces were coated with novel transparent methacrylate-based copolymers. The multifunctionality of the copolymers, such as adhesion to the substrate, surface polarity, mechanical long-term stability in water, and ability to form metal complexes was inserted by the choice of suitable comonomers. The monomer 2-acetoacetoxy ethyl methacrylate (AAMA) was used as complexing unit to produce copper(II) complexes in the coating’s upper surface layer. The semifluorinated monomer 1H,1H,2H,2H-perfluorodecyl methacrylate was employed to adjust the surface polarity and wettability. Comprehensive surface characterization techniques, such as X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that surface compositions and properties can be easily adjusted by varying the concentrations of the comonomers. The formation of copper(II) complexes along the copolymer chains and their stability against washing out with plenty of water was proven by XPS. Copolymers containing semifluorinated comonomers significantly inhibited the growth of Achnanthidium species. Copolymers with copper-loaded AAMA-sequences were able to reduce both the growth of Achnanthidium spec. and Staphylococcus aureus.

Surface–sediment diatom assemblages of the urban ponds of St. Petersburg, Russia

The diatom assemblages of the surface sediments have been studied in 53 urban ponds and lakes of St. Petersburg for the first time. In total, 350 species and infraspecific taxa have been registered; the species of Achnanthidium, Cocconeis, Cyclostephanos, Cyclotella, Gomphonema, Lemnicola, Navicula, Nitzschia, and Stephanodiscus genera were the most common. The wide distribution of small centric planktonic taxa, Cyclostephanos dubius, C. invisitatus, Cyclotella pseudostelligera, Stephanodiscus hantzschii, and S. minutulus, is preconditioned by the depletion of dissolved silica, which is a result of the high phosphorus load. The high abundance of macrophytes in the shallowest sites favors the dominance of epiphytic Fragilaria, Staurosira, and Staurosirella taxa. Bottom-living diatoms in the shallow eutrophic and hypereutrophic urban ponds are light-limited; this is a result of either macrophytes or phytoplankton development. Alkaliphilous and alkalibiontic species prevail among the pH-indicative species, while eutraphentic and hypereutraphentic diatoms, as well as those thriving in a wide range of trophic conditions, dominate over other trophic groups. The β- and α-mesosaprobic species are the most common saprobity-indicative taxa.

Diatom assemblages of non-living substrates in petrifying Cratoneurion springs from lower Belgium

Diatom assemblages were examined from non-living substrates in thirteen springs supporting the Natura 2000 habitat type 'Petryfing springs with tufa formation' in the southern part of Flanders. More than 300 taxa were recorded, including some which appear to be particularly associated with this kind of environment. Even though a number of characteristic taxa and diatoms characterizing fast-flowing springs of more elevated terrain remained absent, local species richness was higher than reported from carbonate springs elsewhere in Europe. Relative abundance of 'Red List' taxa was, however, substantially lower. Taxon richness was not related to measured nutrients but increased with diatom-inferred trophic status. Assemblages consisted mainly of motile, small-celled species of Achnanthidium, Amphora, Caloneis, Planothidium and Stauroneis. Hygropetric rheocrenes presented a somewhat more distinct assemblage than helocrene and rheohelocrene settings, but overall, compositional metrics were similar among spring types. Assemblages were structured mainly along gradients of pH, major ions (in particular magnesium and potassium) and nitrate relating to calcite precipitation, aquifer and nitrogen supply. Besides substantiating broad similarities among Cratoneurion springs, the results provide arguments for a regionalized approach towards assessment of their diversity, community structure and conservation status.

Achnanthidium petuniabuktianum sp. nov. (Achnanthidiaceae, Bacillariophyta), a new representative of the A. pyrenaicum group from Spitsbergen (Svalbard Archipelago, High Arctic)

During a survey of the freshwater littoral diatom flora from lakes and ponds in the region of Petuniabukta on Spitsbergen (Svalbard Archipelago, High Arctic region), a new Achnanthidium species, A. petuniabuktianum sp. nov., has been recorded. Achnanthidium petuniabuktianum is a new representative of the A. pyrenaicum group as evidenced by its curved distal raphe fissures. The present paper describes in detail the morphology of A. petuniabuktianum based on light and scanning electron microscopy. The new taxon is characterized in having linear valves with parallel margins and broadly rounded, never protracted apices and a characteristic—in light microscopy hardly discernible—striation pattern consisting of very short striae composed of one or two small, always slit-like areolae. Based on current results, Achnanthidium petuniabuktianum is a benthic taxon occurring in epilithic and epiphytic habitats in the littoral zones of freshwater lakes and ponds.

Morphological variability within the Achnanthidium minutissimum species complex (Bacillariophyta): comparison between the type material of Achnanthes minutissima and related taxa, and new freshwater Achnanthidium species from Portugal

Two new taxa similar to Achnanthidium minutissimum were common and abundant in samples collected during a survey of benthic diatoms in watercourses from mainland Portugal. They are described here as A. duriense, sp. nov. and A. lusitanicum, sp. nov. In addition, the recently described A. pseudolineare is reported from various localities and its ecology is described in detail. The new Achnanthidium species from Portugal were compared with the type material of morphologically similar taxa: Achnanthidium microcephalum, Achnanthes minutissima, A. minutissima var. cryptocephala, A. minutissima var. inconspicua and A. nana. The analysis of this type material confirmed that Achnanthes minutissima var. cryptocephala should be regarded as a different taxon, and a new combination is proposed, Achnanthidium neocryptocephalum, stat., comb. et nom. nov. Achnanthes minutissima var. inconspicua is now considered as a younger synonym of Achnanthidium lineare. Based on a detailed morphological study of specimens of Achnanthes nana from Scotland, Nepal and Portugal, this taxon is transferred to the genus Achnanthidium as Achnanthidium nanum, comb. nov.

Madinithidium gen. nov. (Bacillariophyceae), a new monoraphid diatom genus from the tropical marine coastal zone

:We studied a group of monoraphid diatom species (Bacillariophyceae, Achnanthidiaceae) found in the marine coastal environment of tropical islands of the Caribbean Sea, western Atlantic Ocean, Indian Ocean, South Pacific Ocean, the Adriatic Sea and the Black Sea. Based on light and electron microscope examination, Madinithidium was formally described as a genus new to science with the generitype defined as Madinithidium undulatum. The characteristic features of the valve structure are a strongly developed sternum and raphe sternum, transapical striae formed by a single areola (macroareolae) positioned in small depressions, elevated virgae and coaxial internal central raphe endings. Furthermore, the striae of both raphe and sternum valves are closed by finely perforated hymenes. Madinithidium and Achnanthidium species are difficult to identify correctly with light microscopy since their valves are small and finely structured. Four species recently described from the western Indian Ocean and assigned to Achnanthidium sensu lato – Achnanthidium capitatum, A. flexuistriatum, A. pseudodelicatissimum and A. scalariforme – possessed morphological features permitting their placement into Madinithidium gen. nov. The above-mentioned species were formally transferred to the new genus.

Four Achnanthidium species (Bacillariophyta) formerly identified as Achnanthidium minutissimum from the Antarctic Region

Four taxa belonging to the complex of species around Achnanthidium minutissimum were found during the ongoing taxonomic revision of the Antarctic freshwater and limno-terrestrial diatom flora. Two taxa were previously described as Achnanthidium lailae and A. sieminskae. Two others were formerly identified as A. minutissimum but detailed light and scanning electron microscopical observations revealed sufficient morphological differences compared to the type of A. minutissimum, to justify their separation and description as new taxa: Achnanthidium indistinctum and A. maritimo-antarcticum. The morphology and ecology of all four taxa are discussed comparing the species with morphologically similar taxa. The biogeographical consequences of the splitting of the former A. minutissimum complex in the Antarctic Region are discussed.

Achnanthidium palmeti (Bacillariophyta, Achnanthidiaceae), a new freshwater species from Réunion Island

Recent survey of the epilithic diatoms in the running waters of Réunion Island led to the discovery of a new species of Achnanthidium. Achnanthidium palmeti sp. nov. belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to the same side of the valve. The new species differs from other taxa in this group by a higher stria density and the areolae morphology along the axial area; moreover, apart from Achnanthidium latecephalum H. Kobayasi, A. palmeti sp. nov. is the only species having raphe vestiges. The new species was found in oligotrophic waters with very low conductivity and circumneutral pH.