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Diatom communities sampled in the vicinity of the Polish Antarctic Arctowski Station (King George Island, South Shetland Islands) have been investigated. Soil and sediment samples were collected from Petrified Forest Creek and Ornithologist Creek valleys. A total of 98 diatom taxa belonging to 30 different genera were recorded in the counts. Nine taxa have a marine origin but all together constitute only 0.14% of all counted valves. Three species: Staurosira pottiezii, Psammothidium germainioides and Sellaphora jamesrossensis dominated the flora. Some differences in the diatom assemblages were observed between soil samples from two stream valleys and between soil and sediments from the same catchment area. The highest species diversity was recorded in samples from the dried-up bed of the Ornithologist Creek, where both freshwater and terrestrial species were found. The soil samples from both investigated valleys showed a comparable number of species, but a different species composition. Based on the PCA analysis a clear separation of the assemblages from both creeks could be observed.

Scanning electron microscopy has revealed variation in the ultrastructure of distinctive isolated pores in or near the central area of raphid diatoms, with different types of pores being restricted to phylogenetic groups. Thus, the widespread use of the term stigma for all such pores not only hides the structural diversity but also obscures the phylogenetic distribution of the different types. This paper provides images of the different types of isolated pores, particularly refining the discrimination of variants within the Cymbellales, and reveals some interesting ecological patterns. Revised definitions of stigmata and stigmoids are proposed, together with the recognition and definition of another type of stigmoid. The restricted distribution of more precisely defined pore types shows the importance of consistent use of terminology and its relevance to phylogenetic studies. [ABSTRACT FROM AUTHOR]

A marine amphoroid diatom, responsible for blooms in 2011 and 2019 in French Atlantic waters was studied using morphology and molecular phylogeny. The highest cell concentrations were reached in the region of Marennes Oléron on 19 August 2011 and were related to a greyish discolouration of gills of oysters and mussels. It was identified as Amphora ostrearia var. minor Grunow, based on morphological characteristics. To ensure the correct identification, type material was re-investigated, using the type slide n° 142 (Cleve & Möller 1878. Diatoms. Part II. Esatas Edquists Boktryckeri, Upsala: 49–108) that enabled us to establish the identity of the taxon. Plastid morphology corresponded to Mereschkowsky's type 8 amphoroid chloroplast, a feature typical for the genus Tetramphora Mereschkowsky. Results of a phylogenetic analysis inferred from a concatenated alignment including the nuclear marker SSU and the chloroplast rbcL indicated that A. ostrearia var. minor was positioned inside the monophyletic clade Tetramphora (Mereschkowsky) Stepanek & Kociolek. This, together with the morphological data, necessitated a transfer of A. ostrearia var. minor Grunow to the genus Tetramphora (Mereschkowsky) Stepanek & Kociolek. In addition, the genetic distances (p-values) from SSU–rbcL sequences were estimated among the species of Tetramphora including T. ostrearia, the generitype. These revealed that the divergence between Tetramphora ostrearia (Brébisson) Mereschkowsky and its variety minor was higher than the mean value within species of the genus. As a consequence, the studied taxon is raised to the species level as Tetramphora minor (Grunow) Nézan, comb. et stat. nov. Toxin analysis of four strains of T. minor revealed the absence of domoic acid production. Pigment analysis of T. ostrearia revealed a high fucoxanthin production, similar to other amphoroid species. [ABSTRACT FROM AUTHOR]

A formal cladistic analysis of the morphological features of taxa assigned to the Orthoseiraceae, including Phycavernosa, Guarreraea and species of the genus Orthoseira is developed for 35 taxa based on 16 characters along with two Melosira species and four biddulphioid species as ingroup taxa as well as Leptocylindrus danicus as the outgroup. A consensus tree of 266 843 most parsimonious topologies suggests that the Orthoseiraceae is monophyletic, and that Guarreraea plus all former species of Orthoseira represent a monophyletic group. This analysis of morphological data did not provide support for the members of the Orthoseiraceae being more closely related to melosiroid or biddulphioid diatoms. Relationships within the monophyletic orthoseiracean group are detailed. Due to the exclusion of the generitype of Orthoseira not possessing carinoportulae which are central tube processes, one of the diagnostic features of the former Orthoseiraceae, other taxon names are described and recognized herein. We recognize and describe a new order, the Liparogyrales, based on the genus Liparogyra for taxa that were previously assigned to Orthoseira. Two families, the Phycavernosaceae, comprising the genus Phycavernosa, and the Liparogyraceae, comprising Guarreraea and taxa formerly assigned to Orthoseira, are described. The genus Liparogyra is composed of three subgenera: the subgenus Liparogyra, the subgenus Porocyclia, and the subgenus Insularis which are diagnosed by synapomorphic features. Based on our analysis, the genus Stephanosira appears to lack synapomorphies. Liparogyra, Porocyclia and Stephanosira had previously been described as genera by Ehrenberg. Guarreraea and one newly proposed genus are also included in the Liparogyraceae. Several other lineages are aphyletic, due to them either being monotypic or without diagnostic features. Thus, a total of 29 species in five genera are recognized within the newly described order and two newly described families. Eighteen new combinations are proposed for the transfer of taxa from Orthoseira to other genera. Homoplasy amongst some of the character states is discussed. The diatom genus Orthoseira as typified by O. americana does not possess carinoportulae, requiring a new approach to the nomenclature and taxonomy of the group. A phylogenetic analysis of the group using morphological data was performed, demonstrating patterns of relationships of the species for this lineage. A new classification for this diatom lineage is presented. [ABSTRACT FROM AUTHOR]

Two unknown diatoms belonging to the genus Brachysira were found during a survey of the moss-inhabiting diatom flora in Canada, Greenland, Iceland and Spitsbergen. Detailed light and scanning electron microscopy revealed sufficient morphological differentiation in valve dimensions and shape, striae density, and ultrastructure for them to be described as new species. The description of Brachysira louiseboydiana sp. nov. and B. hutchisoniana sp. nov. brings the total number of Brachysira species globally to 132. Formal descriptions are presented, each illustrated by light and scanning electron micrographs, and the new species are compared with similar Brachysira taxa worldwide. Additionally, four previously described species which were also observed in the Arctic mosses are discussed. Our findings contribute to a better understanding of the Arctic terrestrial diatom flora. [ABSTRACT FROM AUTHOR]

Background and aims – Small-celled araphid diatoms form an important part of the diatom flora in our rivers and lakes. Although several of these species are frequently reported, their correct taxonomic identity is often obscured due to a lack of good knowledge of the original (type) material. Material and methods – Several historical (nineteenth century) original samples were retrieved from different European and North American diatom collections. The samples have been analysed using light (LM) and scanning electron microscopy (SEM). Key results – Staurosirella crux comb. nov., based on Ehrenberg’s Navicula crux, proved to be the oldest valid name for Staurosirella harrisonii, the latter now being considered a younger synonym. A new European species, S. neorhomboides sp. nov., is described to replace the name S. rhomboides, now considered a younger synonym of S. leptostauron. The North American populations of S. rhomboides and S. martyi differ sufficiently from the type populations and are described as new species: S. moralesii sp. nov. and S. manoyloviana sp. nov. The new combination Staurosirella informis comb. nov. is proposed for a taxon described in 1856 from the French Pyrenees as Odontidium informe. Staurosirella leptostauron turns out to be insufficiently described and is now documented for further use. Conclusion – The analysis of the original (type) material corrected several taxonomic errors and better characterised the morphology of several commonly observed Staurosirella species. [ABSTRACT FROM AUTHOR]

Background and aims – The genus Orthoseira is generally known to be typically aerophilous. Despite the worldwide occurrence of the genus, most of the Orthoseira species seem to have a rather restricted biogeographic distribution, often being part of an endemic diatom flora. During a survey of the aerophilic diatom flora in Papua New Guinea (Karkar Island, Boisa Island), four morphologically distinct Orthoseira taxa have been observed. Material and methods – The morphology of four Orthoseira species was investigated in detail using light microscopy (LM) and scanning electron microscopy (SEM). Key results – The morphology of all four species is discussed and compared to known species worldwide. The main differences between the species include: the presence and shape of linking structures, the number of rows of perforations on the copulae, presence/absence of internal caverns and the external structure of the carinoportulae. Two species, with a unique set of features, are described as new to science: Orthoseira iserentantii sp. nov. and Orthoseira papuensis sp. nov. Conclusions – The observation of four Orthoseira species, including two species new to science, confirms that the diversity of the genus Orthoseira is underestimated. [ABSTRACT FROM AUTHOR]

The region of Bruges (Flanders, Belgium) was an economic and cultural centre during the Late Middle Ages because it was connected to the North Sea via a large tidal inlet called the Zwin, along which smaller towns developed. One of these towns was Aardenburg (Zeeland, The Netherlands), which developed from a Roman castellum to become one of the important medieval towns in the hinterland of Bruges. Unfortunately, archaeological, historical and (palaeo)environmental data about the Roman to medieval evolution of the Zwin area are scarce. However, the continuous occupation of Aardenburg during the first millennium AD and its location on a Pleistocene sand ridge bordering the coastal plain provide a unique opportunity to investigate the natural dynamics of the coastal evolution and the interplay with the human impact that shaped the Zwin region before its heyday. The variable character of the depositional environments on the dynamic coastal plain makes local environmental studies essential for understanding larger patterns, which were previously reduced to a simplistic outdated model over the entire region. Palynological and diatom assemblages of two sequences in Aardenburg allow the reconstruction of the terrestrial and aquatic palaeoenvironments from the Middle Holocene to the high Middle Ages. The results reveal landscape evolution in relation to woodlands, peat bogs, coastal environments and human presence, consistent with previous regional landscape evolution. A distinct increase in marine influence during the Roman and early medieval periods, when human activities played a significant role, was followed by an increase in inland indicators from the high medieval period onwards. This evolution is in accordance with the expansion of the town and the reclamation of the coastal landscape as it evolved to become a cultural centre in the Late Middle Ages. [ABSTRACT FROM AUTHOR]