An algal strain with the morphological characteristics of the Eustigmatophyceae was isolated from a small pond in Itasca State Park, Minnesota, USA. Phylogenetic analyses of the DNA sequences from the nuclear 18S rDNA and the plastid rbcL loci both placed the strain in the order Eustigmatales and family Chlorobotryaceae. The new strain was not clearly allied with any lineage within the Chlorobotryaceae. Morphological features as determined by both light microscopy and transmission electron microscopy were typical for the Eustigmatales, except for the presence of an irregular surface of the cell wall (including the presence of stipitate or digitate projections on some cells) and the production of yellow-orange inclusions in the cytoplasm of cells in stationary-phase cultures. Upon transfer to fresh media, these inclusions are subsequently expunged from the cells during autosporulation. Based on these features and the results of phylogenetic analysis, we describe Flavoaurantia irregularis gen. et sp. nov.

A total of 81 strains morphologically corresponding to the circumscription of <i>Mallomonas intermedia</i> were isolated from 27 freshwater localities across Europe and North America. Molecular genetic analyses revealed two distinct lineages with a strict geographical pattern, which diverged approximately 8 million years ago. According to comparative morphological analyses, we concluded that European populations corresponded to <i>M. intermedia</i>, whereas North American populations were described as a new species, <i>M. retimedia</i> sp. nov. The most notable morphological difference between the species is in the number of pores enclosed in the mesh formed on the siliceous scales. While in <i>M. intermedia</i> the mesh typically surrounds only one pore, meshes of <i>M. retimedia</i> usually encircle 3-4 pores. By incorporating fossil evidence into our time-calibrated phylogeny, we propose that the ancestor of <i>M. intermedia</i> and six related species likely lacked a thick secondary layer but had a distinct transverse rib, present in extant <i>M. galeiformis</i>, <i>M. intermedia</i> and <i>M. retimedia</i> species. The evolutionary history of this group further reveals that parallel ribs on the siliceous scales have evolved independently at least three times during the Miocene epoch, suggesting an adaptive significance, although their exact function remains unclear.

During a survey of the terrestrial moss diatom flora in Greenland, two unknown Humidophila species were observed that could not be identified using the currently available literature. Detailed morphological analysis using both light and scanning electron microscopy revealed sufficient morphological differentiation from known species to describe these as new species: H. helderiana sp. nov and H. mitosis sp. nov. Formal descriptions are presented, each illustrated by light and scanning electron micrographs, and the new species are compared with similar Humidophila taxa worldwide. Additionally, eight previously described species which were also observed are discussed, and Humidophila mochalovae comb. nov., formerly belonging to the genus Diadesmis, was transferred to Humidophila. Of these known species, six have not been previously reported from Greenland, expanding their known geographic distributions. Our findings bring the total number of Humidophila species globally to 87 and contribute to a better understanding of the terrestrial Arctic diatom flora.

The genus Simonsenia is characterized by the raphe system that opens into a longitudinal channel over a marginal keel, and small circular areolae, occluded by hymens. So far, the occurrence of Simonsenia species in Brazil is known only by two records of S. delognei, documented in light microscopy. Here, are described three new species of Simonsenia, one from karst freshwater environments and two from an estuarine stream. Also, we report S. delicatula for the first time to Brazil, in a lotic freshwater body. The new species are distinguished from each other and from similar Simonsenia taxa mainly due to size, valve contour, apices shape, morphology of transapical ribs, and number of areolae rows of the striae. This study is an important contribution to the taxonomy, diversity and distribution of the genus, still underestimated, especially in estuaries and karst of tropical regions.

Chrysophyte stomatocysts are well documented in lake sediments, but except for a few studies on sexually reproducing colonial chrysophytes, little is known regarding encystment cues in these algae. Ochromonas pinguis Conrad, a mixotrophic chrysophyte with an unknown sexual history was observed to produce stomatocysts, albeit at a low frequency. To determine if the low rate of encystment was typical or whether manipulating environmental conditions might enhance the rate of resting cyst production O. pinguis was subjected to various physical and chemical conditions in a batch culture. O. pinguis cultures were manipulated by culturing them in DY-V inorganic medium in variable light, pH, and temperature conditions, and at varying levels of N and P limitation. Except for growth in continuous darkness, all treatments resulted in an increase in O. pinguis concentration. Five treatments resulted in a corresponding increase in stomatocyst concentration. In the remaining treatments stomatocyst production was steady although sporadic. The encystment frequency however was minimal in all manipulations and ranged from 0.008 to 0.03% of the population undergoing cyst formation. In this study, O. pinguis stomatocyst production was not influenced by laboratory manipulations but rather a minute proportion of the population produced stomatocysts regardless of environmental conditions.

The genus Humidophila is mainly characterized by small cells, striae often composed by one elongated areola occluded by thin hymenes. Species are distributed globally and are common in moist sub-aerial habitats. We identified five Humidophila species found in the well-conserved freshwater bodies and subaerial wet habitats from the mountain region "Mananciais da Serra". Four previously known species (Humidophila brekkaensis, H. contenta, H. nienta, H. paracontenta) and one new species (Humidophila piraquarae sp. nov.) were described and illustrated based on light and scanning electron microscopy observations. Humidophila piraquarae sp. nov. is similar to H. nienta (Carter) Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová and H. undulata Lowe, Kociolek, Johansen, Van de Vijver, Lange-Bertalot et Kopalová, but is best distinguished by their prominent constriction, apices broadly rostrate-rounded, striae density, raised siliceous thickening in the apical region of the axial area, and raphe proximal endings laterally expanded in anchorshaped depressions. Addtionally, a list of Humidophila taxa already registered in Brazil is presented.

The historic type material of <i>Microneis gracillima</i>, <i>Navicula pyrenaica</i>, <i>Achnanthes amphicephala</i>, <i>Achnanthes thienemannii</i> and <i>Achnanthidium</i> <i>rostropyrenaicum</i> was investigated together with additional European populations of these species using light and scanning electron microscopy. The morphology of the species was compared to similar taxa. <i>Achnanthes amphicephala</i> is transferred to the genus <i>Achnanthidium</i>. The species are distinguished from each other in the shape of their poles and in valve outline. There are currently very few photographic records of the species, but our results suggest that these species are typical in base-rich, oligotrophic waters, and might be important indicator species for these habitats.

Karst rivers in Croatia are common phenomena and known biodiversity hotspots for many different groups of organisms. Due their importance from a natural, cultural and socio-economic point of view, most of them are protected as National Parks. Diatoms in these habitats are not well known, and recently detailed study has been started. During observations of samples from Lake Visovac on Krka River, one <i>Aneumastus</i> species with specific morphological features, has been recorded. The species is characterized by linear valves with almost parallel margins in the mid-valve, rostrate apices and striae that are partly biseriate, coarsely punctate and distantly spaced. In this study, it is described as a new species <i>Aneumastus </i><i>visovacensis</i> sp. nov. Its morphology is documented with light and scanning electron microscopy, described in detail, and compared with the most similar species from <i>A. tusculus </i>species complex.

The diatom genus Tabellaria Ehrenberg is one of the most widely distributed genera in freshwaters, both in benthos and phytoplankton. It is rather frequent in unpolluted, circumneutral to slightly acidic and poorly mineralized lakes, streams and peat bogs. Despite being studied intensively in the last decades, the taxonomy of this genus is still unsatisfactory as some authors recently proposed to consider most species as synonyms of Tabellaria flocculosa (Roth) KĂźtzing. Several dozen of Tabellaria rich samples from Europe were investigated and six were selected to illustrate typical populations. Five new species are described based on detailed LM and SEM observations: Tabellaria acidodelicata sp. nov., Tabellaria hercynica sp. nov., Tabellaria koppeniana sp. nov., Tabellaria procera sp. nov. and Tabellaria valdeventricosa sp. nov. Additionally, the type materials of T. fenestrata, T. flocculosa and T. ventricosa have been investigated and illustrated together with a discussion on Tabellaria andina stat. nov., at present exclusively found in South America.

Florida is a diverse region that supports abundant cyanobacterial diversity, especially in terrestrial environments. To exploit this environment for cyanobacterial diversity, several greenhouses from central Florida were sampled to identify common nuisance and contaminating algae. Most of the algae observed were mat forming, covering nursery pots, plants, and equipment which were macro- and microscopically morphologically analogous to Brasilonema. Although macroscopic thallus morphology was similar among the samples, microscopic morphological characteristics such as size, color, and sheath formation were disparate. To uncover the cryptic diversity, mats were processed for species isolation, culture, and molecular taxonomic identification. A total of eleven Brasilonema strains were isolated into culture and systematically identified using 16S rRNA and 16S-23S rRNA ITS sequences. Based on morphology and molecular data, five species of Brasilonema were found and three are new to science: B. fioreae, B. santannae, and B. wernerae.