Background and aims – Within the project “German Barcode of Life – Diatoms” common diatoms of German waters were routinely isolated and cultivated. In order to understand the taxonomy and phylogeny of the genus Gomphonema, one of the most common taxa of Central Europe, known currently either under the name Gomphonema olivaceum in Europe or Gomphoneis olivacea in America, was studied. Methods – Twenty unialgal strains were established from five different water bodies in Germany and one from Lake Balaton, Hungary, which supplied molecular data (18S V4 and rbcL) besides morphometric and ultrastructural data. In addition, on eight populations from different water bodies including the type from Denmark, morphometric and micromorphological studies by light and scanning electron microscopy were performed. Key results – Molecular and micromorphological data show that the target taxon neither belongs to Gomphonema Ehrenb. nor to Gomphoneis Cleve. By reinstating the genus name Gomphonella Rabenh., the nomenclatural and taxonomic enigma of this taxon is solved, and with the presentation of the type by Hornemann the authorship of the epithet is clarified. Molecular data for the unialgal strains and several environmental clones show that there is more diversity in the Gomphonella olivacea clade than can be identified morphologically. In addition, the establishment of the new species Gomphonella coxiae and Gomphonella acsiae is supported. The molecular data classified Gomphonella species as belonging to the Cymbellales but not to the Gomphonemataceae. In addition, molecular data put Gomphoneis tegelensis R.Jahn & N.Abarca also into Gomphonella. In order to make the genera Gomphoneis and Gomphonema monophyletic, their astigmate members are transferred to Gomphonella. Conclusions – The results clarify that the gomphonemoid outline is not restricted to the family Gomphonemataceae but seem to be distributed across the entire order Cymbellales. This is shown in this paper for the revived genus Gomphonella, which contains the astigmate group of Gomphoneis and Gomphonema besides the longly disputed G. olivacea. Only a polyphasic approach, combining molecular and micromorphological data for taxonomy, nomenclatural evaluation, and observations from clonal cultures can reveal the full intricacies of evolutionary relations.

Temperature and salinity are some of the most influential abiotic parameters shaping biota in aquatic ecosystems. In recent decades, climate change has had a crucial impact on both factors—especially around the Antarctic Peninsula—with increasing air and water temperature leading to glacial melting and the accompanying freshwater increase in coastal areas. Antarctic soft and hard bottoms are typically inhabited by microphytobenthic communities, which are often dominated by benthic diatoms. Their physiology and primary production are assumed to be negatively affected by increased temperatures and lower salinity. In this study, six representative benthic diatom strains were isolated from different aquatic habitats at King George Island, Antarctic Peninsula, and comprehensively identified based on molecular markers and morphological traits. Photosynthesis, respiration, and growth response patterns were investigated as functions of varying light availability, temperature, and salinity. Photosynthesis–irradiance curve measurements pointed to low light requirements, as light-saturated photosynthesis was reached at <70 µmol photons m⁻² s⁻¹. The marine isolates exhibited the highest effective quantum yield between 25 and 45 S_A (absolute salinity), but also tolerance to lower and higher salinities at 1 S_A and 55 S_A, respectively, and in a few cases even <100 S_A. In contrast, the limnic isolates showed the highest effective quantum yield at salinities ranging from 1 S_A to 20 S_A. Almost all isolates exhibited high effective quantum yields between 1.5 °C and 25 °C, pointing to a broad temperature tolerance, which was supported by measurements of the short-term temperature-dependent photosynthesis. All studied Antarctic benthic diatoms showed activity patterns over a broader environmental range than they usually experience in situ. Therefore, it is likely that their high ecophysiological plasticity represents an important trait to cope with climate change in the Antarctic Peninsula.

Polar regions are among the most extreme habitats on Earth. However, diatom biodiversity in those regions is much more extensive and ecologically diverse than previously thought. The objective of this study was to add knowledge to benthic diatom biodiversity in Western Antarctic coastal zones via identification by means of morphology, DNA metabarcoding and cultured isolates. In addition, a taxonomically validated reference library for Antarctic benthic diatoms was established with comprehensive information on habitat, morphology and DNA barcodes (rbcL and 18SV4). Benthic samples from marine, brackish and freshwater habitats were taken at the Antarctic Peninsula. A total of 162 clonal cultures were established, resulting in the identification of 60 taxa. The combination of total morphological richness of 174 taxa, including the clones, with an additional 73 taxa just assigned by metabarcoding resulted in 247 infrageneric taxa. Of those taxa, 33 were retrieved by all three methods and 111 only by morphology. The barcode reference library of Antarctic species with the new references obtained through culturing allowed the assignment of 47 taxa in the metabarcoding analyses, which would have been left unassigned because no matching reference sequences were available before. Non–metric multidimensional scaling analyses of morphological as well as molecular data showed a clear separation of diatom communities according to water and substratum types. Many species, especially marine taxa, still have no record in reference databases. This highlights the need for a more comprehensive reference library to further improve routine diatom metabarcoding. Overall, a combination of morphological and molecular methods, along with culturing, provides complementary information on the biodiversity of benthic diatoms in the region.

Diatom cultures can help answer taxonomic, biogeographic and ecological questions on a local and global scale. Unialgal cultures are derived from a single cell and provide abundant material for morphological and molecular analyses. The link between the historic morphological species concept and the molecular data is becoming increasingly important with the use of eDNA metabarcoding. Additionally, cultures provide insights into the life cycle of diatoms and thereby complement taxonomy and species ecology. In this study, we present an approach to extract benthic diatoms from an environmental sample to generate unialgal cultures. We explored diatom diversity in preserved assemblages and by culturing as many different taxa as possible from benthic freshwater samples taken on the same day from the Bow River in Calgary, Canada. With both methods we found a total of 221 different benthic diatom taxa, of which 182 were identified in the preserved diatom assemblages. Interestingly, an additional 39 taxa only appeared in the cultures. In total 129 strains were cultivated representing 71 different taxa. This study includes pictures of living cells demonstrating the additional merits of unialgal cultures, as they provide information on plastid details, auxospores and endosymbionts. Both, the identification of the diatom assemblages and the generation and identification of strains provide the foundation for additional water quality assessment tools, taxonomic insights and molecular references libraries.

The monoraphid diatom Cocconeis scutellum is considered to be the most common marine species of the genus Cocconeis. It has been reported from the littoral zones of marine and brackish waters worldwide. Described by Ehrenberg, it is the type of the name of the genus Cocconeis. Many varieties of C. scutellum have been described during the last two centuries; some have since been raised to specific rank. In recent years, high-resolution SEM and molecular methods have helped to better understand the boundaries among taxa and to study their geographic distribution. Despite several recent studies revising type material of other Cocconeis taxa by morphological and molecular characters, the type of the generic name has not yet been studied, nor have cultures from the type locality been established. We present molecular (rbcL, 18SV4) and morphological (LM, SEM) data for 18 Cocconeis strains that were isolated from the type locality in the southern Baltic Sea at Wismar, Germany, and match Ehrenberg's type material. Preserved material from one strain is designated as the epitype of C. scutellum. An emended species description is provided. Citation: Skibbe O., Mora D., Schimani K., Abarca N., Kusber W.-H., Huck V., Zimmermann J. & Jahn R. 2026: Morphomolecular characterization and epitypification of Cocconeis scutellum (Bacillariophyceae), type of the diatom genus Cocconeis. – Willdenowia 56: 185–208. Version of record first published online on 23 March 2026.