Laurencia Lamouroux (Rhodophyta) was recently separated into three genera – Laurencia, Chondrophycus (Tokida et Saito) Garbary et Harper and Osmundea Stackhouse – each of which was newly defined based on vegetative and reproductive structures. In this study, the previously unknown vegetative and reproductive morphology of two Australian endemic species of Laurencia, L. clavata Sonder and L. elata (C. Agardh) Harvey, was studied, particularly in the context of the revised generic delineation. These species exhibit vegetative axes with four pericentral cells and trichoblast-type spermatangial development. Tetrasporangia are abaxially produced from the existing third and fourth pericentral cells. L. clavata has terete thalli with distinctive verticillate branching and is similar to Chondria C. Agardh, rather than to Laurencia, in having an unusually marked constriction at the base of the branches and starch accumulation in subcortical and medullary cells. Compared to Laurencia, apical cells of this species exhibit a less oblique division; the resulting recognizable axial cell rows extend somewhat below the branches, and particularly at a young stage they are also clear throughout branchlets. However, other vegetative and spermatangial structures show that L. clavata is more closely allied to Laurencia than to Chondria, and it is placed in Laurencia. By contrast, L. elata exhibits morphology typical of Laurencia and is characterized by large, robust, compressed thalli with fastigiately distichous branching and an extensive secondary cortex. Furthermore, it appears to be distinct from similar species in sometimes having a parasitic species of Janczewskia Solms-Laubach (Rhodophyta). Taxonomy of Laurencia is discussed on the basis of these and previous studies.

Three Cocconeis Ehrenberg species, epiphytic on the leaves of Posidonia oceanica (L.) Delile, were studied by light and electron microscopy. A new species, C. pseudonotata, is described which is closely related to C. notata Petit and C. diruptoides Hustedt. Gross morphology and the presence of a sigmoid raphe and sternum are the characters shared by the three species, whereas the central areas of sternum and raphe-sternum valves, and the stria and areola densities are the main distinctive characters for the species when observed by light microscopy. Scanning and transmission electron microscopic observations revealed that the fine structure of areolae must be also considered in order to identify the species. Comparison among the three species has been carried out by observations on material from our samples, as well as on the type material of C. diruptoides and cleaned samples from the Hustedt collection. The study also provides new information on the geographical distribution of these species.

The development of auxospores and initial cells of the freshwater chain-forming diatom Ellerbeckia arenaria forma arenaria was studied using light and electron microscopy. Whether the auxospore mother cell is formed vegetatively (parthenogenesis) or through autogamy is still a matter for speculation. Because no signs of spermiogenesis could be detected in our material, we exclude oogamy. Further development involves retraction of the protoplast from the epivalve and the formation of a featureless siliceous cap with a central opening on its free surface. The homology and function of this cap remain uncertain. At the other end of the cell the protoplast remains tightly attached to the hypovalve throughout its further development. This hypovalve always has a concave valve face. An organic wall bearing many layers of overlapping, small silica scales begins to be formed while the cell is still enclosed within the mother cell wall, and allows the auxospore to swell, thus breaking the siliceous cap and girdle bands. External and internal surfaces of scales can be distinguished morphologically. Initial valves are formed internal to the scales at an oblique angle to the parent chain. The initial epivalve always faces the hypotheca of the auxospore mother cell, and the initial valves already show elements of the heterovalvy manifest in the vegetative cells. The significance of the observations in terms of ecology and phylogeny is discussed. The combinations Ellerbeckia arenaria (Moore ex Ralfs) R. M. Crawford, and E. arenaria forma teres (Brun ex Schmidt) R. M. Crawford are made.

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.

Complete nuclear 18S rRNA and chloroplast 16S rRNA coding sequences of the fusiform green alga Closteriopsis acicularis (G. M. Smith) Belcher et Swale (Chlorophyta) were used to determine its phylogenetic position within the Chlorophyta. Phylogenetic trees inferred from both genes show that C. acicularis is most closely related to Chlorella kessleri Fott et Nováková (Trebouxiophyceae) and does not belong to the family Selenastraceae (Chlorophyceae) as proposed previously. Despite its morphological distinctness, C. acicularis has to be placed close to the genus Chlorella Beijerinck, and especially to C. kessleri. The chloroplast 16S rRNAs of C. acicularis and C. kessleri possess a unique insertion resulting in an additional AT-rich helix in a length-conserved region of the gene. A close relationship to the genus Chlorella is further confirmed by the pyrenoid ultrastructure. The 16S rRNA gene of C. acicularis contains a group I subgroup IA3 intron which is most similar to the first intron in the corresponding gene of Chlamydomonas pallidostigmatica King (Chlorophyta). In helix P6, the intron carries an additional extension related to intron-encoded endonucleases of the LAGLIDADG family. It is the first group I intron reported in chloroplast 16S rDNA of a species other than Chlamydomonas.

The red alga Caulacanthus okamurae Yamada occurs commonly on the coasts of South Korea, but reproductive plants have rarely been found in the field. Seasonality of field populations was examined and the temperature responses of growth and reproduction were determined in laboratory cultures. In the field, monthly average temperatures of surface seawater ranged from 12·7 °C±0·73 (SD) to 21 °C±1·19. Monthly mean biomass in 25×25 cm quadrats (n = 3) ranged from 11·2±9·6 g m−2 (SD) to 148·8±19·2 g m−2 in wet weight with minimal biomass in February 1995 and maximal values in August. In culture, the growth of vegetative plants and germination of tetraspores of C. okamurae occurred at temperatures from 13 to 27 °C. Tetrasporangia, gametangia and cystocarps were formed at 19 °C and above, but not at 13 or 16 °C, indicating that reproduction is directly affected by seawater temperature. On the basis of these data, seawater temperature was above the critical temperature for reproduction from August to October (20–21 °C) yet only three plants with tetrasporangial branches were found in the field. In September the biomass of C. okamurae declined sharply following severe storm damage. Thus, the absence of reproductive organs in field populations of C. okamurae may occur because they inhabit a seasonally stressful habitat, in which typhoon damage removes branches before the water temperature becomes favourable for reproduction.

Gene expression in Fucus vesiculosus L. from the Ria Formosa, Faro, Portugal was investigated by screening a cDNA library generated by suppression subtractive hybridization (SSH) for algae undergoing mild desiccation stress (60–70% tissue water content). The subtractive library was constructed from small amounts (1 μg) of total RNA using PCR-based techniques. Screening by reverse Northern analysis (cDNA Southerns) revealed that between 60% and 70% of clones randomly selected from the library were differentially regulated in desiccated and hydrated algae. Most genes could not be directly identified based on sequence homology with known gene sequences. However, several cDNAs for chloroplast-encoded transcripts were identified and shown to be up-regulated or differentially regulated in desiccated algae relative to hydrated controls. These included partial sequences for ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco; rbcL/rbcS), chloroplast coupling factor ATPase (atpH/atpI) and a photosystem I P700 chlorophyll a binding protein (psaA). The usefulness of reverse Northern analysis was confirmed with conventional Northern analysis of transcript abundance for Rubisco, which varied rapidly in response to light and the hydration status of the algae. These results show that SSH is a useful technique for analysing the responses of gene expression to environmental stress, and as a starting point for the subsequent identification of stress-responsive genes in macroalgae.

Carotenoid contents of terrestrial cyanobacteria sampled from rock surfaces with different exposure to sunlight were studied in the Guyana-shield region of Venezuela. At the collecting locations of two table mountains Roraima-tepui (2700 m), Auyan-tepui (2000 m) and an inselberg near Puerto Ayacucho (80 m), the most frequent species were Stigonema ocellatum, Stigonema hormoides and Scytonema crassum, respectively. Usually, these species were associated with the unicellular cyanobacterium Gloeocapsa sanguinea. Their carotenoid and chlorophyll a contents were determined by high-performance liquid chromatography. In general, carotenoids consisted almost equally of myxolglycosides and of β-carotene derivatives, such as β-carotene, echinenone and canthaxanthin. On a chlorophyll a basis, myxolglycoside content increased in full exposure to solar irradiation. The relative proportions of the different β-carotene derivatives appeared to be even more strongly influenced by irradiance. Whereas their total amount was increased at full exposure, the content of β-carotene decreased and that of canthaxanthin increased. Maximal ratios of canthaxanthin/β-carotene of around 5 were observed in the most sun-exposed samples. We conclude that acclimation of the carotenoid content to irradiance, especially the adjustment of the ratio canthaxanthin/β-carotene, is a response found in many different terrestrial cyanobacterial species. However, when a natural population was artificially shaded for 6 days, short-term acclimation in pigment content was not detected. The results support a photoprotective function of canthaxanthin in terrestrial cyanobacteria under natural environmental conditions.

The reproductive structures in Actinotrichia fragilis (Forsskål) Børgesen are described, including the first report of the structure and development of the carpogonial branch and cystocarp for the genus. Tetrasporangia usually arise in a terminal position on assimilatory filaments; occasionally they are formed laterally and in a secund manner. In male thalli, conceptacles are initiated from the apical pit of a thallus branch. Filaments bearing spermatangia issue from the inner face of the conceptacle wall. In female thalli, a carpogonial branch consists of a carpogonium, hypogynous cell and basal cell. Carpogonial branches may arise in two ways, either replacing a vegetative branch or rarely as a third branch between vegetative dichotomous branches. Before fertilization, the hypogynous cell divides to produce four cells. Subsequently, the basal cell produces branched filaments that eventually form the pericarp, which envelops the carpogonial branch and developing gonimoblast. After fertilization, the carpogonium divides transversely into two cells. The upper progeny cell retains its cytoplasmic connection to the trichogyne. The lower cell produces a lateral gonimoblast initial. Primary gonimoblast filaments form a compact pseudoparenchymatous mass at the base of the carposporophyte. Carposporangia are produced singly from the tips of the secondary gonimoblast filaments, which develop from the primary gonimoblast mass. Many simple or little-branched sterile paraphyses issue from the inner face of the pericarp and grow into the cavity. A comparison of the reproductive structures of Actinotrichia with those of the other genera of the Galaxauraceae suggests that the genus is closely related to Tricleocarpa Huisman et Borowitzka and Galaxaura Lamouroux.

Over the course of nearly a year, counts were made of the algae present in the samples from a Burkard-type volumetric aerobiological trap which sampled continuously the atmosphere of the city of Badajoz (SW Spain), yielding hourly and daily results. The method permits only the major taxa of algae to be distinguished. Most of the algae found belong to the Chlorococcales (Chlorophyceae) and small centric diatoms (most of them Cyclotella). Some filamentous algae were also found and even Pediastrum coenobia as well as lichen soredia. Up to 12 Chlorococcales coenobia per cubic metre were found. The mean number of cells in the coenobia was more than 10, although some coenobia with more than 100 cells were observed. Their greatest concentration was during the months of May and June. The mean daily concentration of diatoms was highly variable, with maximal concentrations of more than 70 cells m−3 in June. The maximum daily concentration of lichen soredia was 5 m−3, with the concentration being fairly constant throughout the year but particularly high in spring and early summer. The hourly distribution showed maxima during the day and minima during the night. Significant positive correlations were found with temperature, and negative correlations with relative humidity in the three groups studied. The wind speed seemed to have a positive influence on the concentration of diatoms and Chlorococcales coenobia, although the direction of the wind also had an effect.

Previous laboratory studies in species of the Laminariales have revealed that both the onset of growth in early winter and the summer drop in growth rate are controlled by the annual course of daylength synchronizing endogenous, circannual clocks within the thallus. Moreover, it is known for some laminarian species that cultivation in the laboratory in constant short days (SD) leads to arhythmic, continuous growth activity of the blade throughout the year. Such a prolonged SD treatment has now been performed for the first time in outdoor-cultivated Laminaria digitata. Field-grown sporophytes were collected in May from the sea near Helgoland (North Sea) and cultivated on the island of Sylt (North Sea) in temperature-controlled outdoor tanks (300 l) at 10 °C for 1·5 years either in a constant 8 h of light per day, controlled by an automatic blind on top of the tank, or in ambient daylengths. In constant SD, the growth rate remained at a steady-state level of approximately 0·4 cm day−1 from the end of June until mid-October, whereas growth rate in ambient daylengths declined steadily after June to half the rate in SD in October. Growth became light-limited between October and February in both treatments and, in the second year from July onwards, higher growth rates were again observed in constant SD than in ambient daylengths. Further work is required to find out whether SD treatment in summer would also prevent the summer drop in growth rate in other perennial seaweed species, e.g. commercially valuable red algae. This would potentially increase the chance of more constant biomass production throughout the year, and decrease the danger of the cultivated perennial algae being overgrown by annual epiphytes in summer.

Branch structure and growth in Amphiroa generated by primarily dividing apical medullary cells was documented by light and scanning electron microscopy. Specific numbers of long- and short-celled tiers are formed when intergenicular and genicular medullary cells periodically divide, leading to the unit pattern concept. Zonations on the intergenicular surface, grooves on the decalcified intergenicular surface and spaces in longitudinal section of intergenicula underlie units. Three unit pattern types are recognized: angled medullary tiers arranged in a straight horizontal row with lateral initials cut off abruptly from peripheral medullary cells in A. annulata and A. anastomosans (type A), medullary tiers whose length gradually reduces as they curve into the cortex in A. fragilissima var. debilis, A. rigida var. antillana, A. spina and A. verruculosa (type B), and rounded medullary tiers arranged in slightly irregular horizontal rows with lateral initials or cortical cells surrounding circularly peripheral medullary cells that are cut off from the medulla in A. cuspidata (type C). These patterns were statistically analysed in four Bermudan species: A. annulata, A. cuspidata, A. fragilissima var. debilis and A. rigida var. antillana. Unit patterns can usefully distinguish species. The association of intergenicula and genicula at the branch apex during the initial stage of branch formation is explained for the following four species: A. annobonensis, A. crustiformis, A. fragilissima var. debilis, and A. itonoi.