Biological classification has been successively shaped by Neoplatonism, ideas of plenitude and one-dimensional continuity (the Great Chain of Being), two-dimensional continuity (Linnaeus's map), idealized comparative morphology and development and, through phylogenetic theory, Darwinian descent with modification. Concepts of Algae have thus evolved within a succession of very different paradigms. Algae have been imperfect plants; a segment of the Great Chain; the least-developed members of vegetative form-series; and primitive forms from which plants (and even animals) can be elaborated. The idea of a single grouping of simple organisms, formalized by Bory de Saint-Vincent and others in the early nineteenth century, was developed in a phylogenetic framework by Haeckel as Protista. Most macrophytic algae, however, remained Plants until Copeland merged eukaryotic non-green algae into Protista. Arrangements of algal taxa within form-series, and recognition of Algae and Protista as taxa, are incompatible with Hennigian phylogenetic systematics (cladistics). Developing genomic perspectives threaten to undermine established concepts of organismal lineage and higher-level biological classification.

The marine red alga Laurencia japonensis sp. nov. (Rhodomelaceae, Ceramiales) is described from the warm temperate region of Japan. It is characterized by the following combination of features: (1) terete, rigidly cartilaginous, upright axes arising from a primary discoid holdfast and stolon-like branches; (2) tristichous branching; (3) penultimate and ultimate branches showing pronounced adaxial bending; (4) adventitious branches formed chiefly in the axils; (5) the production of four periaxial cells per vegetative axial segment; (6) the presence of longitudinally oriented secondary pit connections between contiguous superficial cortical cells; (7) the absence of projecting superficial cortical cells; (8) the absence of a radially elongated cortical layer; (9) the presence of abundant lenticular thickenings in the walls of medullary cells; (10) the presence of a single corps en cerise per superficial cortical cell and trichoblast cell; (11) a parallel arrangement of tetrasporangia; (12) broadly ovoid cystocarps with the lower half immersed within the parent branch tissue; and (13) distally positioned spermatangial nuclei.

The habitat of the acido- and thermophilic red algae Galdieria sulphuraria and Cyanidium caldarium was examined in acidic hot sulphur springs in the vicinity of Naples (Italy). These species grew on soil and rocks, but a large part of the populations was cryptoendolithic. The endolithic algal layer (1–3 mm in thickness) was covered by amorphous silica (1–2 mm in thickness) containing traces of hydrotroilite (FeS.nH2O) and elemental sulphur. Organotrophic bacteria and fungi were not found in the algal layer. Light penetration measurements showed that 0·1–1% of the sunlight reached the upper part of the algal layer. Thus, low-light-adapted algae should be able to perform some photosynthesis in this endolithic habitat. Under conditions where light is even more limited, e.g. in winter or after darkening of the covering layer, many of the cells might not survive. Aqueous extracts of these algae are excellent growth substrates for Galdieria sulphuraria. Therefore, we propose that compounds released from dead cells in the endolithic layer are used by the surrounding Galdieria cells for heterotrophic metabolism. This would increase their chance of surviving prolonged periods under detrimental conditions.

Effects of nitrogen (N) and phosphorus (P) limitation on calcification and coccolith production in Emiliania huxleyi were investigated in batch and chemostat cultures by means of chemical analyses of calcium (Ca) and organic carbon (C), counts of coccoliths and cells, and scanning electron microscopy. In a normally calcifying (C-cell) clone growing in the absence of nutrient limitation in batch or semi-continuous cultures, c. 36 attached plus detached coccoliths were present per cell. In batch cultures as well as in chemostats, the number rose to 70–120 when either N or P became strongly limiting. The molar Ca/C ratio, measured in chemostats, showed a corresponding increase from 1·07 to c. 1·38. The two types of limitation had opposing effects on the calcification of individual coccoliths: the mean Ca content of a coccolith decreased from a normal value of 0·60 pg to 0·46–0·49 pg under N limitation, and increased to 0·67–0·73 pg under P limitation. These effects were accompanied by corresponding modifications of coccolith morphology. In batch cultures of one naked (N-cell) clone grown to the stationary phase, P limitation but not N limitation induced the formation of c. 40 coccoliths per cell; these coccoliths were of aberrant shape. In another N-cell clone, P limitation had no such effect. The results suggest on one hand that coccolith formation is generally less dependent on N and P nutrients than is cell replication, and on the other hand that stages exist in the growth and calcification of a coccolith that are specifically influenced by either N- or P-containing cell constituents.

In the red alga Bostrychia moritziana, release of spermatia is triggered by slight osmotic shock; they emerge under pressure apparently generated by swelling of the mucilaginous sheath. Spermatia adhere tenaciously to trichogynes of the carpogonium. Adhesion triggers spermatial mitosis, which is complete in about 30–45 min; there is no cytokinesis and the binucleate spermatium becomes vacuolated. The delicate, dynamic trichogyne cytoplasm contains complex membranous components and vacuoles. At the contact zone, the trichogyne and spermatial wall erode, forming a pore, and cytoplasmic continuity (plasmogamy) is achieved after about 50–70 min. Many trichogynes rupture during these events because of inadequate structural connection with the spermatia. Normally, both spermatial nuclei enter the trichogyne in sequence; rarely, both nuclei enter together. Entrance is rapid, and the nuclei often become thin and greatly elongated as each squeezes through the narrow pore into the trichogyne. Once inside, each nucleus resumes its normal shape as it starts to move steadily along the trichogyne, often with irregular pauses. One nucleus of each pair (not necessarily the first out of the spermatium) migrates along the trichogyne towards the carpogonium base to fertilize the female nucleus; the other moves in the opposite direction, away from the entry site, and it often ends up near the tip of the trichogyne. This same scenario was observed for each of several spermatia contributing nuclei to one trichogyne. Thus, our observations indicate that the two nuclei in each spermatium are differentiated so that only one is capable of fertilization, differentiation being visibly expressed in the direction that the nucleus moves as it enters the trichogyne.

The green alga Chlamydomonas reinhardtii can use the ureides allantoin and allantoate as sole nitrogen sources. Once the uptake systems for allantoin and allantoate were induced, the uptake and growth rates were identical for the two ureides. However, the enzymatic activities involved in the degradation of the two ureides (allantoinase and allantoicase) were regulated differently. Allantoinase seems to be constitutive, since it was detected in all the nitrogen sources studied, while allantoicase behaved as an inducible enzyme, since it was present only in cells cultured in ureides or any metabolic precursor of these compounds. Neither allantoinase nor allantoicase activities were repressed by ammonium in the presence of ureides. Allantoicase activity was not induced under nitrogen starvation conditions, while it was induced in cells that had been cultured with allantoin or allantoate in the dark. Allantoin uptake showed a pattern similar to that of allantoate under all nutritional and environmental conditions tested. Inhibition of allantoin and allantoate uptake by N-ethylmaleimide suggests that thiol (SH–) groups are involved in both uptake systems. The use of both allantoin and allantoate was similarly inhibited by the metabolic poisons tested (cyanide, azide, 2,4-dinitrophenol and 3′-(3,4-dichlorophenyl)-1′,1′-dimethyl urea) but only at very high concentrations. The possibility that uptake of allantoin and allantoate might take place through two independent systems is discussed.

The brown algal family Chordaceae contains the single genus Chorda with two terete unbranched species, C. filum and C. tomentosa. They share a similar superficial morphology, but differences in anatomy and reproductive characters have made assignment to a single genus controversial. Comparison of DNA sequences of variable parts of the small subunit of the nuclear ribosomal cistron, and of relatively conserved areas of both internal transcribed spacers, of several taxa of the Sporochnales–Desmarestiales–Laminariales complex revealed that the two species of Chorda are not closely related and do not form a clade. This is taken as support for recognition of Halosiphon tomentosus (Lyngbye) Jaasund, although it was originally based on the erroneous observation of a Streblonema-like gametophyte in the life history of H. tomentosus.

Ulva armoricana sp. nov. is described from the coast of Brittany, France, using the taxonomic criteria established by Bliding, Koeman and van den Hoek for the European species of Ulva. Morphological evidence strongly suggests that Ulva armoricana is conspecific with the free-living Ulva populations responsible for the ‘green tide’ phenomenon that occurs at some eutrophicated sites in North Brittany. Blades of U. armoricana are variable in shape, fragile, easily torn, and 30–55 μm thick in middle and apical regions; they differ from those of U. olivascens by their pale green colour and from those of Ulva lactuca, U. rotundata, U. gigantea, U. pseudocurvata and U. curvata by their crumpled texture that creates an irregular light-reflecting surface, and by the presence of tooth-like protuberances at the margin of the blade. U. armoricana differs from U. scandinavica in having longitudinal ribs containing closely packed bundles of rhizoids, except in the youngest thalli. U. armoricana can be discriminated from U. rigida by the polygonal (never rounded) cells in the mid-thallus region, and quadrangular cells arranged in small longitudinal rows in rapidly growing parts. Pyrenoid number, 1–2 (3–4), overlaps with that of other species, and shape of non-rhizoidal cells of the basal region in transverse sections, either oval or with tapered ends, appears not to be a good taxonomic character. Herbarium data indicate that the species has been collected in northern France since at least 1869, but was previously unrecognized.

The utility of rDNA internal transcribed spacer (ITS) sequences for separating species of Ulva along the North Brittany coast of France was investigated. Particular attention was paid to the Ulva species responsible for ‘green tides’. Floating thalli are difficult to identify due to fragmentation and it was not clear at the outset whether one or more species of Ulva might be contributing to the green tide phenomenon. Results show that ITS sequences are good markers for Ulva species and that the Lannion Bay green tide taxon is a previously unrecognized species that can also be identified on morphological grounds. We found that ITS type did not necessarily correspond to the initial identification of a specimen based on morphological features, due to the lack of good diagnostic characters. This survey highlights the need for a more intensive survey of Ulva populations along European coasts. Once ITS groups can be recognized, quick screening assays can be developed to aid morphological identification.

Production of phytochelatins (PCs) in response to cadmium uptake in the benthic macroalgae Vaucheria compacta and V. debaryana (Xanthophyceae) was investigated. The algae synthesized thiol-containing peptides, identified by means of high-performance liquid chromatography as PC2, PC3 and PC4. In both algal species the level of PCs increased with time of cadmium exposure and was dependent on external cadmium concentration. V. compacta synthesized significantly more PCs than V. debaryana. Exposure of the algae to cadmium at low temperature and in darkness resulted in a significant decrease in PC content over the time interval tested (3 days).