The Uruguay River is the second most important river in the Río de la Plata Basin. Taxonomical composition, abundance and distribution of cyanobacteria collected at nine sampling stations in the Lower Uruguay River (Uruguay) were analyzed seasonally from 2006 to 2009. A total of 24 taxa were identified, including 13 Chroococcales, 4 Oscillatoriales and 7 Nostocales species. The genera Dolichospermum and Microcystis presented the highest number of species among the planktic water bloom-forming cyanobacteria. The highest densities of cyanobacteria were recorded in summer during a bloom, with 6.2×106 cells.ml-1, and the most abundant species were Microcystis aeruginosa and Dolichospermum cf. pseudocompactum. In this case, the toxicity analyses by
HPLC did not indicate the presence of microcystin-LR. Phytoplankton growth in the Uruguay River was found not to be nutrient-limited. The high correlation of cyanobacteria densities with nitrogen and phosphorous compounds is directly related to changes in flow. Cyanobacteria densities increased with summer high temperatures in low flow conditions. The ANOSIM analysis showed no significant differences between zones and sampling sites, but there were temporal significant differences in relation to seasonal samplings. Radiocystis fernandoi Komárek et Komarková-Legnerová was recorded for the first time in Uruguay and Dolichospermum cf. pseudocompactum (Watanabe) Wacklin et al. was recorded for the first time in South America.

The cyanobacterial genus Phormidium is polyphyletic, as follows from recent molecular and phenotypic analyses. Several isolated clusters were found also in Antarctic populations (Taton et al. 2006, Taton et al. 2010, Strunecký et al. 2010b). A few of them have already been described or revised on the generic level (e.g., Phormidesmis, Microcoleus). One of the separate clusters belongs to a group of strains identified traditionally as Phormidium murrayi, described from the Antarctica originally in 1911 as Lyngbya murrayi by W. et G.S.West. We evaluated 23 morphologically similar strains or populations resembling Ph. murrayi from the Antarctica and few other geographical regions; 6 of them were studied by us by molecular methods. Morphological characteristics and 16S rDNA similarity corresponding with typical Ph. murrayi were shared mostly by the specimens from the Antarctica. Molecular analyses confirmed that Ph. murrayi represents a special taxonomic group (on the generic level) inhabiting commonly shallow freshwater classified as a special genus in cyanobacterial taxonomy (Wilmottia gen. nov.) according to the recent "polyphasic approach". The type species of Wilmottia, W. murrayi, was determined up to now to be characteristic for the Antarctica. Other phylogenetically and morphologically similar types from other regions represent possibly different taxa (species) of the same generic unit. The specific status of similar or related strains from other regions should be therefore solved in the future.

A new aerophytic species of the xanthophycean genus Excentrochloris - Excentrochloris fraunhoferiana Hofbauer, Gärtner, Rennebarth, Sedlbauer, Mayer et Breuer from a building surface is described. Light microscopically investigation and sequence analyses showed a clear relationship of the new alga to Botrydiopsis
constricta Broady. Cytomorphology and reproduction of the new species was investigated on cultures. E. fraunhoferiana differs from the type species E. gigas by bigger size of adult vegetative cells with obligate thickening of wall, and none amoeboid zoospores with one chloroplast. Adult zoospores are peripherically arranged in the sporangia. The relation to Botrydiopsis constricta is discussed in comparison with characters of E. fraunhoferiana.

An aerophytic Nostoc, from a Mayan monument, has been characterized by phenotypic and molecular approaches, and identified as a morphospecies of Nostoc commune. Phylogenetic analysis indicates that it belongs to a Nostoc sensu stricto clade, which contains strains identified as N. commune. Nostoc cf. commune is found in two close areas: Site I (protected from direct sunlight by a wall), where it forms biofilms on mortar with Trentepohlia
aurea; and Site II, where it grows on exposed stucco with the accompanying organism Scytonema guyanense. Over the year, in a habitat dictated by alternating wet and dry seasons, the organisms vary in appearance. Its life cycle comprises two seasonally-determined developmental stages (growth during the wet season and dormancy during the dry season) and two transitional stages (preparation for the dry season, and rehydration and recovery). At the beginning of the wet season the resistant stages from the previous dry season are rehydrated and form propagula, that adopt a colonial shape surrounded by a gelatinous sheath. As conditions become drier, clearly more in Site II, N. cf. commune employs adaptative strategies agains the drought, such as reducing the number of cells inside thick ensheathed colonies. Akinetes were observed, although only in Site II and in cultures of an isolated strain. Their fine structure shows parallel arrays of whorled thylakoids and septal intercellular connections. Spectral confocal laser scanning microscopy was used to analyze the fluorescence spectra of the photosynthetic pigments. N. cf. commune shows phycocyanin, allophycocyanin and chlorophyll a in both sites. Moreover, spectra of vegetative ensheathed cells, collected at Site II at the dry season, differed in their fluorescence spectrum: they feature a peak at 564 nm, attributed to phycoerythrin, which increases cell tolerance against the detrimental effects of strong light. These findings indicate that both the distribution and persistence of N. cf. commune might stem from cumulative adaptative strategies that increase its resistance to extreme desiccation.

The CAUP (Charles University in Prague) image web-database of algae is mostly based on the heritage of the German personalities who were working at the German part of Charles University from the second half of the 19th century to the 1945. Database includes at present 275 images of herbarium specimens, 1,710 images of permanent slides and 1,044 images of living algal strains from CAUP culture collection; in total 1,135 specimens. Nevertheless, many objects in the University collection remained to be non-digitalised and the original species names of objects have been only partially revised.

To clarify the distinctiveness of the genus Cyanospira from the related genus Anabaenopsis, a morphological study of several undescribed strains of Cyanospira and an extensive phylogenetic analysis of Anabaenopsis and Cyanospira were performed.
Heterocytous cyanobacterial strains were isolated from natron salt samples from the Republic of Chad containing large numbers of dormant dry akinetes. Morphology, and the entire life cycle, from akinete germination to the development of mature vegetative forms, were documented. Cultures of Cyanospira, obtained from the germination of desiccated akinetes, were characterized by variable filament dimensions and coiling degrees. Akinete development in vegetative filaments was typically apoheterocytic; akinetes developed in chains continuously expanding along the filament; in old cultures, the whole filaments could be transformed into chains of akinetes. The development pattern of akinetes in Cyanospira was definitely different from that of Anabaenopsis. Phylogenetic analysis was performed using the ARB and SILVA phylogenetic tools and databases. All publicly available sequences of strains belonging to the genera Anabaenopsis and Cyanospira, and sequences of our new strains, were compared with selected entries of Nostocaceae. The two genera Anabaenopsis and Cyanospira formed two phylogenetically coherent and well defined sister units, mostly related to the genus Nodularia. Inside
the Anabaenopsis branch, a cluster exclusively composed by strains of A. elenkinii and another corresponding to A. nadsonii could be identified. Sequences of Cyanospira formed two distinct phylogenetic clusters, respectively corresponding to the species C. rippkae and C. capsulata. Sequences of the alkaliphilic species A. abijatae were found to be members of the C. rippkae subcluster.
As already known for halophilic cyanobacteria, also alkaliphilic cyanobacteria of the genus Cyanospira were phylogenetically separated from their mesophilic counterparts, classified under the genus Anabaenopsis. We support that the differentiation of sister genera in response to selective conditions of extreme environments is a well represented evolutionary mechanism in cyanobacteria.

The coccoid green algae Coenochloris planoconvexa and Echinocoleum elegans are assigned to different families (Radiococcaceae and Oocystaceae, respectively), but display similar ray-like mucilaginous envelopes. Molecular analysis of the 18S rRNA gene of C. planoconvexa CAUP H 5502 and E. elegans SAG 37.93 revealed that they both belong to Oocystaceae. However, the two strains were not a part of a monophyletic cluster. Furthermore, their morphology differed, namely in the shape of their mucilaginous envelopes, and in their ability to form four-celled units in a broadened sporangial wall. Because the name Coenochloris cannot be used for members of Oocystaceae, a new genus Ooplanctella, with the type species O. planoconvexa comb. nova, is proposed.

The type material of Gomphonema rosenstockianum LANGE-BERT. et E. REICHARDT from La Gomera (Canary Islands, Spain) and epilithic material of rivers from several European countries were examined using light and scanning electron microscopy in order to improve the knowledge on the taxonomical status of the G. rosenstockianum and G. tergestinum (GRUNOW) M. SCHMIDT species complex. Two other Gomphonema species, G. supertergestinum E. REICHARDT and G. angustius E. REICHARDT, recently described and belonging to the same group, are also presented in detail. After the analysis of several populations of G. rosenstockianum and G. tergestinum it was possible to define several reliable criteria to allow morphological differentiation of both species under LM and SEM as well. A geometric morphometric analysis clearly demonstrated the separation of these taxa considering valve outline, size and shape of the central area and position of the stigma. Apart from the morphological analysis, compilation of the results of this study has also revealed differences in ecological preferences of the two species. World and European distribution maps of the four Gomphonema taxa are presented.

The diversity of microeukaryote communities inhabiting rivers is still poorly known. Here, we have analyzed the periphytic and planktonic microeukaryote communities present in one section of the River Danube by two different methods: 18S rRNA-based terminal restriction fragment length polymorphism with fragment sequencing and microscopical analysis of the phytoplankton and periphyton. Both data sets were then related to environmental variables. Molecular fingerprinting revealed diverse communities with fluctuating composition, with the majority of sequences affiliated to the groups Bacillariophyta, Synurophyceae and Chlorophyceae. This was in accordance with microscopical data. The total number of detected T-RFs during the study period was 145, with more than half of the T-RFs being restricted to either plankton or periphyton. This suggests that the likely different natural selection regimes experienced by microeukaryotes in these two environments may promote the presence of different lineages in each of them. Significant correlations were found between phytoplankton chlorophyll-a content, phosphorus content, temperature, and the T-RFLP pattern of the planktonic microeukaryotic community, suggesting that the former environmental factors are especially important in structuring the planktonic microeukaryote communities in the River Danube. These data, together with earlier studies suggest that molecular methods are an invaluable addition in pursuit of the better understanding of the diversity and fluctuation of freshwater microeukaryotic communities.

Forest soils of the Great Smoky Mountains National Park were examined for soil algae as part of the All Taxa Biodiversity Inventory underway in that park. Soils of both mature and secondary growth forests were sampled, along with samples from rocks and tree bark. A total of 42 taxa were observed, representing Cyanobacteria (3 species), Chlorophyceae (12 species), Trebouxiophyceae (18 species), Ulvophyceae (3 species), Klebsormidiophyceae (1 species), Zygnematophyceae (2 species), Tribophyta (3 species), Eustigmatophyta (1 species), Euglenophyta (1 species), and Dinophyta (1 species). Twenty new taxa records for the park were established.

Rust-coloured shells of the aquatic gastropod Ventrosia ventrosa, a new record for eastern Greece, indicating presence of iron (EDAX analysis) were studied for detection of iron-encrusted photosynthetic epibionts in a Greek brackish-water thermal spring (38 °C). Microscopic analyses (LM, SEM) revealed the presence of a biofilm consisted of mostly facultative micro-epibionts, i.e. a) 5 periphytic taxa of coccal and filamentous cyanobacteria, including a taxonomically and ecologically interesting morphospecies, Xenococcus cf. pyriformis, dominated exclusively on the shell surface, and b) pennate diatoms with higher species richness (18 periphytic taxa of the genera Amphora, Brachysira, Cymbella, Diatoma, Encyonema, Navicula, Nitzschia, Pleurosigma, Synedra, Ulnaria; 5 taxa as new records for Greece), most of them emerging only after acid treatment of whole gastropod shells. The abundant diatoms thriving directly or nearby the iron-coatings (Cocconeis placentula var. euglypta and Achnanthes brevipes sensu lato) exhibited different modes of attachment ('adnate' and 'pendunculate', respectively). Two euendolithic cyanobacteria (Hyella sp. and Leptolyngbya terebrans; the former with special taxonomic interest) were also found perforating the delicate gastropod shells, with no distinct differentiation in the extent of infestation between live and dead gastropod shells. Moreover, the possible impact of these encrusted photosynthetic assemblages on V. ventrosa was investigated; statistical analysis showed that a) there is no 'drag effect', induced by the epibionts, influencing the gastropod growth (i.e. shell length), b) shell size enlargement provides a favourable space and promotes the intense fouling by both micro-epibionts and macro-epibionts (egg-capsules), and c) the detachment prevention of egg-capsules is attributed to the biofilm development.

The present paper focuses on selected cymbelloid diatom taxa inhabiting Nur Sphagnum bog in northern Mongolia. Samples collected in this area contained numerous species of Encyonema KÜTZING and Cymbopleura (KRAMMER) KRAMMER, that are together acidobiontic, oligotraphentic taxa. Cymbopleura pernaviculiformis, Cymbopleura deviatkinii and Encyonema marvanii are described as species new to science. Furthermore, for two other species we suggest new nomenclatural combinations. The characteristics of Cymbopleura naviculiformis (AUERSWALD) KRAMMER sensu stricto are discussed in order to compare it with other species mentioned in this paper. The autecological characteristics of the new species found in Nur bog are presented.

Several unicellular green algae exhibit a unique type of cell division, which can be likened to budding. These algae comprise Spongiochrysis hawaiiensis in Cladophorales (Ulvophyceae) and Stichococcus ampulliformis and species of the genus Marvania in the class Trebouxiophyceae. We determined the 18S rRNA gene sequence from Marvania aerophytica NEUSTUPA et ŠEJNOHOVÁ and inferred its phylogenetic position. Our analyses demonstrated that M. aerophytica is unrelated to other species of the genus Marvania (including the type species M. geminata), but together with S. ampulliformis forms a lineage within a broader clade comprising also species of the order Prasiolales, Desmococcus spp., Gloeotilla spp., and non-monophyletic Stichococcus spp. We discuss morphological characteristics of M. aerophytica and S. ampulliformis and based on our results, we propose M. aerophytica and S. ampulliformis be reclassified into a newly established genus of "budding" green algae, Pseudomarvania, as Pseudomarvania aerophytica, comb. nov. and Pseudomarvania ampulliformis, comb. nov.

A rarely recorded centric diatom of the genus Hyalodiscus was found in three mixed freshwater and brackish environments of Tonga. Both classical morphological and scanning electron microscopic features were used to classify the taxon within currently know taxa from inland and brackwater sites. We recorded stable ultrastructural features (e.g. type of poroids, type and arrangement of rimoportulae) but also several variable morphological features (mainly outline, diameter and structure of the umbilicus and nodulation within the umbilicus centre) as well as variable ultrastructural features (margin of central area; central termination of striae). The loculate nature of puncta closed by rotae and the small fultoportulae potentially typical features for the genus was confirmed. The taxon showed a high similarity to Hyalodiscus lentiginosus JOHN 1982 described from Swan river estuary Australia with the exception of more variable punctation in the central umbilicus area and different variability of central noduli. We also checked for identical features (size, central area) with Hyalodiscus withneyi described by EHRENBERG 1870 from near Great Salt Lake Utah.

Two species of Nupela were identified in a spring and in a small spring-fed pool in the Polish Tatra Mts, - these were N. lapidosa and Nupela sp. The second species is described as N. marvanii. The new species is characterized by heteropolar, narrowly elliptic valves with capitate apices. Sternum valve has very short, sometimes rudimental raphe branches. Under a light microscope transapical striae are not discernible. Externally both valves are covered with hymen. The central area of sternum valves has irregular silicate thickenings. Proximal raphe fissures are straight and terminate in small pores. Distal raphe fissures double-deflected into the same side of the valve, form ?-shaped structures that extend onto the mantle. Internally visible linear-lanceolate axial area, which forms unilateral fascia on raphe valve, which reaches valve margin. Proximal raphe fissures are T-shaped. Distal raphe fissures are straight, and terminate in small, linear helictoglossa. Sternum valve has large, clearly visible internally, asymmetrically lanceolate central area and discernible externally reinforced median costa. Raphe fissures are strongly reduced, rudimental. The areole are round to elliptical, expanded along the transapical axis, with the wider opening on the external surface. An irregular row of similar areoles is present along pleural side of valve. Both species are documented with LM and SEM micrographs and briefly discussed. The distribution and autecology of 46 Nupela members are summarized.

Four new species of the recently established genus Navigiolum (Naviculaceae, Bacillariophyceae) are described from samples collected in ephemeral rock pools of Algeria (North Africa). These species are compared with three similar taxa, recently described from comparable habitats in Sardinia (Italy). With a single exception, Navigiolum is currently composed of species that can be considered endemic elements of the circum-mediterranean region and of unusual autecology. They are living in small freshwater pools that are subject to extreme fluctuation. The seven populations and several more from Sardinia and Algeria appear closely related under light microscopy but can be clearly distinguished in the scanning electron microscope. Four new species, Navigiolum marvanii, N. algeriense, N. simplex and N. densistriatum are proposed.

As a step towards a global monograph of the freshwater diatom genus Sellaphora, we made detailed surveys of Sellaphora diversity in the epipelon of 38 lakes and ponds and three Holocene diatomites in the British Isles, restricting our analysis to those specimens that would be classified in S. americana, S. bacillum, S. pupula or S. laevissima according to the standard European diatom flora of KRAMMER & LANGE-BERTALOT (1986; Süsswasserflora von Mitteleuropa, vol. 2/1. - G. Fischer, Stuttgart & New York). From a total of c. 104 specimens observed, over 3200 were recorded as digital images and sorted into 54 mostly informally-named phenodemes that can act as operational taxonomic units during future revisions. Of the 54 phenodemes, c. 40 are well-differentiated, while the others seem to intergrade and are in particular need of further study using morphometric, molecular and mating approaches. The limitations of conventional diatom taxonomy by visual comparison are clearly demonstrated. To help standardize identifications, published DNA sequences are assigned to some of the demes as 'molecular barcode'. The phenodemes of S. pupula sensu lato cannot be equated with the infraspecific taxa previously recorded for the British Isles and both these and most other pre-1990 records of species now assigned to Sellaphora must be regarded as having very little value for ecological and biogeographical purposes. Possible non-British records of the phenodemes are discussed but few are totally convincing; of those records most likely to be of the same phenodemes, the majority come from elsewhere in Europe.

The River Axe, a lowland river in South-west England is used as a model system for describing how ecological status assessments can be applied in practice. Seasonal sampling over a three-year period established a strong baseline against which future changes could be assessed. These indicated that the river was enriched with nutrients and that ecological status was significantly below the good/moderate status boundary, implying the need for a Programme of Measures to be implemented. Reductions in both point and diffuse sources of nutrients led to changes in the diatom assemblage, reflected by increasing EQRs at monitored sites. An understanding of the uncertainty inherent in diatom-based ecological status assessments allows the success of control measures to be assessed. In the case of the River Axe, diatom-based assessments suggest that the river is now close to good status at many monitored sites, although there is still evidence of some nutrient enrichment.

Live and treated materials from three populations of diatoms collected in Italy, Slovakia and Spain, identified in previous inventories as Navicula stroemii HUST. sensu KRAMMER et LANGE-BERTALOT, were examined under light and scanning electron microscopy. The analyses highlighted the typical single H-shaped plastid, characteristic of the genus Sellaphora. Considering this, we thoroughly investigated type materials from the Sellaphora stroemii complex. According to the standard European diatom flora of KRAMMER & LANGE-BERTALOT (1986: Süßwasserflora von Mitteleuropa 2/1), six species should be considered as taxonomic synonyms of Navicula stroemii, now Sellaphora stroemii (HUST.) H. KOBAYASI in MAYAMA et al.: Navicula aggerica E. REICHARDT, N. rivularis HUST., N. subbacillum HUST., N. subcontenta WILLI KRIEG., N. vasta HUST. and N. ventraloides HUST. The type materials of these species were examined using both light and scanning electron microscopy and geometric morphometric analysis. The analysis of the valve ultrastructure demonstrated the affiliation of Navicula aggerica, N. subbacillum, N. vasta and N. ventraloides to the genus Sellaphora. A Principal Component Analysis based on the shape of the valve outline, allowed us to define the European taxa Sellaphora stroemii, S. ventraloides and S. aggerica as three separated taxa, clearly distinct from the Indonesian diatom Sellaphora subbacillum, comb. nov. Moreover, considering the need of a replacement name for Navicula subcontenta (KRIEGER 1943), already validly published by HUSTEDT in 1942, we propose the new name Navicula petrmarvanii nom. nov. for KRIEGER's species.

Planothidium engelbrechtii (CHOLNOKY) ROUND et BUKHT. was originally described in 1955 from South Africa as Achnanthes engelbrechtii CHOLNOKY. It became necessary to revise the original type material because of some discrepancies between the original description and figures and the current allotment of this species to the genus Planothidium. The present study confirms the transfer of A. engelbrechtii to Planothidium. A lectotype is designated from Cholnoky's original material. Valves from the type material are illustrated and discussed by means of LM and SEM micrographs.

The traditional cyanobacterial genus Anabaena is heterogeneous, as follows from the modern molecular evaluation. The cluster of planktic Anabaena-morphotypes with gas vesicles in cells must be separated as a unique generic entity from the typical benthic mat-forming species. In the present articles all planktic morphospecies are transferred into the new genus Dolichospermum in agreement with Botanical nomenclatoric rules. The name "Dolichospermum" is based on a taxonomic category of section in starting point publication (Bornet & Flahault
1888), which is valid for heterocytous cynobacteria.

The cell morphology of Achnanthes thermalis var. rumrichorum Lange-Bertalot, a first record for the territory of Slovakia and in Europe, was studied under LM and SEM and documented by micrographs. This diatom was found in the benthos of a gravel-pit lake in Bratislava and in artificial thermal basins in the health-resort park of Piešťany, Western Slovakia. A discussion of the morphological features of this taxon and their taxonomic affinities with related species is presented.

In many coastal states the presence and impacts of harmful dinoflagellates have been investigated and documented in the literature. Scientists and government officials in many countries routinely monitor their coastal waters for harmful algae in order to prevent harvesting of contaminated seafood. But this is not the case for Nigeria, a coastal state in the Gulf of Guinea, West Africa. The present work reports findings from a first attempt to monitor potentially harmful algae in the coastal waters of Nigeria. Samples were collected from specific locations that included a coastal sea, a lagoon, estuaries and creeks along Nigeria's coastline in November 1999 and April 2001. Potentially harmful dinoflagellates recorded during these periods included 3 Ceratium species, 5 Dinophysis species, 3 Gonyaulax species, 1 Gymnodinium sp, 1 Lingulodinium species, 4 Prorocentrum species and 1 Scrippsiella species. The potential ecological and human health risks associated with similar species in the literature are highlighted.

The nominate varieties of the monoraphid diatoms Cocconeis pediculus EHRENBERG and C. placentula EHRENBERG are typified. Discrepancies from common concepts in Ehrenberg's types, habitats and descriptions were discovered which might affect our current understanding of both Cocconeis species. To ensure stabilization of names and concepts for these two taxa, epitypes from a location in Berlin close to the locus typicus are presented. Monoclonal cultures of these two taxa have been established. Morphological and morphometric data from clones as well as from populations for both taxa are presented. The taxonomy of C. pediculus and C. placentula var. placentula is discussed and evaluated in the context of historical and recent publications.

The incunabula and perizonium of a paedogamous Neidium deme (in the N. ampliatum species complex) are described in detail using light and scanning electron microscopy. The incunabula contain two types of element, both heavily silicified. At each pole of the ellipsoidal zygote there is a large cap, which almost abuts its twin on either side of the zygote, beneath the gametangial valves. The caps are deeply and widely notched on their 'girdle' sides (i.e. on the sides of the zygote that underlie the gametangial girdle) and the space created by the notches is filled by large, almost triangular incunabular plates. Thus, on each side of the equator of the zygote there is one cap element and two plate elements. The caps overlap the plates and must precede them ontogenetically, creating a polarity opposite to that of the transverse perizonium. Both elements are sparsely and irregularly porous and have fimbriate margins. During auxospore expansion, the two sets of incunabular elements separate at the equator of the cell and the transverse perizonium is formed beneath, the incunabula continuing to form a tight seal around the perizonium and apparently constraining development to form a linear tube. All transverse perizonial bands possess delicate fimbriae and are open, even the primary band, which is slightly wider than the bands on either side and bears a median ridge. The open ends of the secondary bands sweep strongly towards the centre of the auxospore, producing a very obvious and wide suture. In expanded auxospores, a robust longitudinal band is found beneath the suture, which has coarser fimbriae than the transverse bands. Possible interpretations of the incunabular elements are discussed: no structures similar to the incunabular plates have been described in other diatoms, but it is known that related genera (Biremis, Muelleria) also have large cap-like elements in their incunabula. The open nature of the primary transverse perizonial band is unusual in raphid diatoms, but auxospore coverings have been investigated ultrastructurally in too few diatoms to permit detection of evolutionary trends.

Conjugates (Zygnematophyceae) represent the most species-rich (ca. 4000 spp) algal lineage within the Streptophyta. Studies using various molecular markers have placed the class as one of the crown groups in Streptophyta and even suggested a close relationship between the zygnematophycean algae and land plants. Phenotypic diversity complicates systematics of the class and the relationships between its taxa remain poorly understood. Molecular phylogenetic analyses have established a number of clades in the class and revealed a disagreement between the traditional taxonomic structure of Zygnematophyceae and the pattern of phylogenetic relationships between the class members. In this paper, an overview of recent advances in our understanding of the phylogeny and classification of conjugating green algae is presented, with emphasis on the major clades established in the class, the clades' structure and polyphyly of some genera. We describe the areas of conflict and agreement between molecular phylogeny and traditional morphology-based taxonomy and stress that phenotypic characters provide little evidence for inferring relationships between taxa even at low taxonomic levels.

This paper reports on five species of the genus Gomphonema, which seem to be widespread at least in Siberia or in other regions, too. Due to their wide distribution their knowledge is of special importance. Three species are described as new (G. demersum, G. jergackianum and G. marvanii) based on light- (LM) and scanning electron microscopical (SEM) investigations. Important characters delimiting these species from similar taxa are discussed. For two recently described species (G. liyanlingae METZELTIN et LANGE-BERTALOT and G. khentiiense METZELTIN, LANGE-BERTALOT et NERGUI) ultramicroscopical details or SEM micrographs are presented for the first time and additional data on their distribution are given.

This small tropical cyanobacterial group, containing Anabaena volzii Lemmermann and a few related species (A. fuellebornii SCHMIDLE, A. unispora GARDNER, A. mysorensis GONZALVES & KAMAT), differs substantially phenotypically from all other planktic or benthic Anabaena types, mainly by the subsymmetric structure of the trichomes, type of akinete formation and restricted ecology. The taxonomic uniformity of all other Anabaenalike clusters (typical benthic Anabaena, planktic Anabaena subg. Dolichospermum, Trichormus, Aphanizomenon, Cuspidothrix) was already supported by molecular analyses. All of them also have their typical morphological markers, which are clearly different from the "Anabaena volzii - cluster". Therefore, this group can not be classified in any of the mentioned revised genera and must be described as a separate generic entity of heterocytous cyanobacteria (although they have not been sequenced to date). The new genus Macrospermum is therefore defined in my article with 4 related, morphologically distinguishable species. The generic name is selected according to the unusually large akinetes.

The substrate specificity of Lemnicola hungarica (Grunow) Round et P.W. Basson was studied on five Lemnaceae species using material from the Herbarium Generale of the Hungarian Natural History Museum. Diatom assemblages inhabiting Lemna minor, Lemna gibba, Spirodela polyrhiza and Wolffia arrhiza were dominated by Lemnicola hungarica, in contrast to assembladges on Lemna trisulca dominated by Cocconeis placentula. An initial or post-initial cell of Lemnicola hungarica has been found in the studied material.