In the ablation zone of glacier habitats, cryoconite holes are known to harbor diverse microbial communities, including unique diatom floras distinct from those of surrounding aquatic and terrestrial systems. Besides descriptive studies, little is known about the diversity of cryoconite diatoms and their response to environmental stressors, particularly in low-latitude glaciers. This paper documents an extremely diversified diatom community in Antisana Glacier (Ecuador), reporting 278 taxa found in 54 surface holes, although with low individual abundances. Contrary to our expectations, assemblage structure did not respond to water physical or chemical characteristics, nor to cryoconite hole morphology, but to elevation. We demonstrate that elevation is a driver of diatom assemblages. Both alpha diversity (measured as Fisher's index) and species richness (corrected for unequal sample sizes) correlated negatively with elevation, suggesting a replacement toward simplified, poorer communities along this gradient. The taxonomic composition also changed significantly, as revealed by multivariate statistics. In summary, cryoconite holes are sites of high taxonomic diversity composed of taxa that are allochthonous in origin.

Diatom and water chemistry samples were collected from 49 lakes, pools and rivers on Byers Peninsula (Livingston Island, South Shetland Islands) during the summer of 2009. A diverse diatom flora of 143 taxa was found. Fragilaria capucina s.l., Psammothidium papilio, Navicula dobrinatemniskovae and several Nitzschia taxa dominated the flora. The biogeographical analysis showed that more than 55% of all observed taxa presented a restricted Antarctic biogeographic distribution and only 30% had a cosmopolitan distribution, contrary to previously published data. Cluster analysis and Principal Components Analysis were used to classify the samples based on their chemical characteristics, revealing that nutrients and specific conductance were the main factors dividing the samples into four groups: young lakes, coastal lakes, larger lakes on the central plateau and smaller, temporary pools. Diatom communities corresponded well to this division and were strongly influenced by salinity and nutrients.

Amphora angusta Gregory, Amphora ventricosa Gregory and Amphora macilenta Gregory have been misunderstood for the last 140 years. Gregory described these species from sublittoral sediments off the west coast of Scotland. Although the illustrations were excellent for their time (1857), it is impossible to be confident of identification using Gregory's paper, and subsequent authors have created such confusion that records of these taxa must be regarded as untrustworthy unless backed by photographic evidence. In this paper, the first to describe in detail the recently established genus Seminavis, we show that A. angusta is in fact a species of Amphora Ehrenberg, whereas A. ventricosa sensu Gregory represents two independent species of the genus Seminavis D. G. Mann, namely Seminavis ventricosa (Gregory) Garcia-Baptista (non S. ventricosa sensu Garcia-Baptista 1993) and Seminavis arranensis Danielidis & D. G. Mann, sp. nov. The form usually known as A. ventricosa is neither of these and requires a new name, Seminavis robusta Danielidis & D. G. Mann, sp. nov. The long forgotten and misclassified species A. macilenta Gregory is shown to be yet another Seminavis species, requiring a new combination as S. macilenta (Gregory) Danielidis & D. G. Mann, comb. nov.; contrary to previous claims, it is separate from A. ergadensis Gregory, which is a true Amphora. Valve and girdle ultrastructure, plastid arrangement and auxosporulation are described for Seminavis and resemble those in the Naviculaceae sensu stricto.

Examination of sediment samples from oligo-and dystrophic ponds, lakes and streams in Papua New Guinea, Australia and New Zealand revealed a hitherto unknown diversity of the diatom genus Actinella Lewis. Six new species are proposed, viz. Actinella aotearoaia sp. nov., A. giluwensis sp. nov., A indistincta sp. nov., A. muylaertii sp. nov., A. parva sp. nov. and A. pulchella sp. nov. All species are heteropolar, both in girdle and valve view. Novel information on the genus Actinella includes the observations of two ribbon-shaped, valve-appressed plastids in A. aotearoaia and A. pulchella, and the presence of long mucilage stalks in A. aotearoaia. It is argued that, despite recent proposals to reduce the genera Actinella and Desmogonium Ehrenberg to the rank of subgenera of Eunotia, they should be kept separate until the taxonomic significance of their distinctive morphological features (such as heteropolarity) is fully assessed. The new species appear to be endemic to Australasia and have distinct biogeographies within this region. Except for A. aotearoaia, all species are present in Tasmania; A. indistincta and A. pulchella have also been found in New Zealand (Stewart Island). A. aotearoaia is common in several localities in New Zealand but was also found near Sydney on the Australian mainland. Actinella giluwensis has only been observed in material from Papua New Guinea. The record of A. punctata for the latter country constitutes the first confirmed record for this species outside North America and Europe. The discovery of the new Actinella species again confirms the importance of the Australasian region as a major centre of microalgal biodiversity and endemism.

The allogamous raphid diatom Achnanthes longipes C. A. Agardh possesses a complex breeding system involving interactions between three types of clone: monoecious, unisexual and bisexual. Previous studies showed that these three types can be crossed with each other, with a tendency for sexual characteristics to be inherited: inbred monoecious lineages gave rise to monoecious or, very rarely, to bisexual clones, while inbred unisexual lineages yielded unisexual and bisexual clones. The current paper reports on the progeny of crosses between monoecious and unisexual clones and their inbred offspring. All three types of clone appeared in the F1 and F2, although unisexual clones of opposite sex to the parental clone were not found. Inbreeding depression was observed and also a tendency for ‘normal’ auxosporulation (producing two auxospores per pair of gametangia) to be replaced by ‘reduced’ or ‘intermediate’ auxosporulation (producing one auxospore per pair). In addition, patterns of incompatibility were observed that were not seen during earlier studies of clones isolated directly from nature. These included the inability of some F1 clones to mate with each other, in spite of compatibility with all other clones examined (unisexual, bisexual and monoecious).

Haslea ostrearia, the peculiar diatom that develops in oyster-ponds and synthesizes a water-soluble blue pigment (marennine), was grown in a semi-continuous mode over a wide range of irradiances (20–750 μmol; m−2 s−1). Growth, photosynthesis and pigment content were determined for algae maintained in exponential growth phase by regular dilution with fresh medium. Increasing the growth irradiance resulted in a decrease in the chloroplast length, but had no clear influence on the size of the cellular compartments pigmented by marennine accumulation. Growth rates increased with irradiance from 20 to 100 μmol; m−2 s−1 and were constant from 100 to 750 μmol; m−2 s−1. Increasing growth irradiance caused a decrease in the cellular content of chlorophylls a and c and fucoxanthin, in contrast to diadinoxanthin. Algae acclimated to high irradiance had lower maximum photosynthetic rate (Pnm) and maximum light utilization coefficient (α) when expressed on a per cell basis. On a chlorophyll a basis, the higher the growth irradiance, the lower the maximum light utilization coefficient and the higher the maximum photosynthetic rate. No photoinhibition was observed at irradiances up to 1500 μmol; m−2 s−1 whatever the growth irradiance. In vivo chlorophyll a fluorescence showed that cells grown at high irradiance had effective photosystem II quantum efficiency (measured at the growth irradiance) considerably lower than that of cells grown at low irradiance. Thus H. ostrearia withstands high light exposure, consistent with the observation that this alga can outcompete other diatoms encountered in oyster-ponds characterized by low turbidity and shallow depth.

This paper continues a series of studies of the allogamous raphid diatom Achnanthes longipes, which has a complex reproductive system combining unisexual, bisexual and monoecious behaviour. Following earlier work on the effects of inbreeding in the progeny of crosses between two unisexual clones, we studied the progeny of clones that are capable of a high degree of selfing in monoclonal culture (‘monoecious clones’). Three generations of selfed progeny were examined. In addition, we investigated the F1 generation obtained after crossing two different monoecious clones. Monoecious clones produced monoecious or, more rarely, bisexual progeny, but did not give rise to unisexual progeny. As in inbred lineages made by crossing closely related unisexual clones, inbreeding in monoecious lineages leads to a reduction in the number of gametes formed by the gametangia, from two to one. Inbred clones exhibit marked inbreeding depression and only three inbred generations were possible in monoecious lineages. In the third, final inbred generation, monoecious sexual reproduction was initiated in monoclonal cultures but gametes rarely fused and none of the auxospores and initial cells that were formed were viable; this also occurred when the inbred clones were crossed with any of the other clones available. The significance of inbreeding and other aspects of the breeding system in A. longipes is discussed.

A new raphid pennate diatom genus, Eunophora, and three new species are described from highland lakes and streams in Tasmania and New Zealand. Eunophora tasmanica and E. indistincta are only found in Tasmania; E. oberonica and a fourth species (Eunophora sp. 1) also occur in New Zealand. The presence of polar rimoportulae in E. tasmanica and E. oberonica, the relatively simple structure and arrangement of the raphe system and the stria pattern indicate that Eunophora belongs to the subclass Eunotiophycidae. However, it differs from the other genera in this subclass in the amphoroid symmetry of the cells, the length of the raphe slits and the non-coaxial internal central raphe endings; also unusual are the position of the raphe on the valve face instead of on the ventral mantle and the presence of many small discoid or band-like chloroplasts. Eunophora may represent a link between the Eunotiophycidae and the amphoroid genera of the Bacillariophycidae. Eunophora is characteristic of dystrophic to (ultra-)oligotrophic lakes and appears to be restricted to the Southern Hemisphere. The four species display a characteristic distribution in Tasmania: Eunophora tasmanica is common and widespread in all highland lakes, E. oberonica occurs mainly in the dystrophic western lakes, while E. indistincta and Eunophora sp. 1 were found mainly in intermediate lakes along the limnological corridor between the western dystrophic lakes and the eastern oligotrophic lakes.

A new diatom genus and species, Australodiscus peruvianus Porguen et Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The valve outline is stellate with ocelli and rimoportulae situated singly on alternate points of the star. The rimoportulae are winged and situated on a secondary marginal ridge. Three types of spines are present; two of these are also winged. Our new form appears to be best placed for the present in the centric family Triceratiaceae (Schütt) Lemmermann, being most closely related to the type genus Triceratium Ehrenberg and Grovea A. Schmidt.

Deux espèces très rarement signalées, Cymbella alpina et C. stauroneiformis, ont été étudiées au microscope optique et aumicroscope à balayage. La caractérisation des sous-genres Encyonema, Cymbella et Cymbopleura est revue à l'aide de trois exemples : Cymbella minuta, C. cistula et C. helvetica. La position systématique de C. alpina et de C. stauroneiformis par rapport aux autres taxons étudiés et par rapport aux différents sous-genres ou la récente réapparition d'anciens genres est discutée.