Three Chordaria species were reported from the Russian Far East, viz. C. chordaeformis, C. flagelliformis, and C. gracilis. Chordaria flagelliformis and C. gracilis are common and widely distributed in the Bering Sea and Kamchatka, Kuril Islands, and the Sea of Okhotsk, while C. chordaeformis was only reported from the Avacha Bay (southeast Kamchatka). We describe a new species, Chordaria okhotskensis, from the Taujskaya Bay (northern Sea of Okhotsk, Russia). The external morphology of C. okhotskensis is similar to C. chordaeformis in having unbranched or sparsely branched thalli with branches borne at acute angles. The new species differs from C. chordaeformis in having large elongate medullary cells and thalli that are entirely flattened. Phylogenetic analysis based on rbcL gene data showed that this new species from the Sea of Okhotsk is distinct from the Atlantic and Pacific types of C. chordaeformis. Based on the phylogenetic results, the Kamchatka specimens of C. chordaeformis were also attributed to a new taxon, C. okhotskensis.

Rhodachlya hawaiiana Kurihara, J.A. West, Conklin et A.R. Sherwood sp. nov. is described based on cultured material from the island of Hawaii as the second member of the genus Rhodachlya. The pit plug ultrastructure of this alga is characterized by the presence of inner and outer cap layers but lacking a cap membrane between the layers, which is a diagnostic feature of the order Rhodachlyales and the genus Rhodachlya. Morphologically, R. hawaiiana is distinctive from R. madagascarensis in vegetative cell dimensions, frequency of colorless hair cell formation, and spore germination pattern. Rhodachlya hawaiiana and R. madagascarensis are also distinguishable by their nuclear SSU rRNA gene sequence divergence (p-distance = 0.0064), which is comparable to other species-level divergences among members of the Nemaliophycidae.

Rhodachlya hawaiiana Kurihara, J.A. West, Conklin et Sherwood sp. nov., décrite à partir de materiel cultivé provenant de l'île d'Hawaii, est la seconde espèce appartenant au genre Rhodachlya. L'ultrastructure des synapses de cette algue montre la présence d'une couche interne et d'une couche externe recouvrant le bouchon synaptique, sans membrane de revêtement entre les couches, ce qui est une des caractéristiques de l'ordre des Rhodachlyales. Morphologiquement R. hawaiiana diffère de R. madagascarensis par la taille de ses cellules végétatives, par la fréquence des cellules formant des poils hyalins et par le mode de germination des spores. Ils diffèrent aussi par la séquence de leur SSU rRNA avec une divergence (p-distance=0.0064) comparable à d'autres divergences entre espèces parmi les Nemaliophycidae.

A new species of Codium, C. apiculatum P.C. Silva, M.E. Chacana et H.B.S. Womersley, is described on the basis of several subtidal collections from southern and southwestern Australia. It is characterized by its utricles, which are stout, subcylindical to slightly clavate, bearing several hairs (or hair scars) very close to the apex, and by the branch tips, which are apiculate.

Taxonomic revision of the traditional polyphyletic cyanobacterial genus Phormidium is based on molecular sequencing combined with the definition of distinct, autapomorphic features. Several genera, clearly separated from each other (with genetic similarity lower than 95%), were already defined and separated from this widely conceived generic unit (Phormidesmis, Wilmottia and others). All of these new generic taxa are characterized by morphological markers also. We have studied another group of species (mainly the strains from salterns in Thailand), which was classified earlier in the genus Phormidium, but it represents an isolated cluster according to 16S rRNA gene sequencing and is characterized by specific uniform and morphological features. Because this whole group represents a phylogenetically and morphologically distinctly separated cluster (see Phormidium group I sensu Komárek & Anagnostidis 2005), we describe it as a special taxon Oxynema genus novum, in agreement with the Botanical Nomenclatoric Code (ICBN; McNeill & al. ed., 2007). The genetically most related clusters always have genetic similarity less than 93% and differ by distinct autapomorphic features. The filaments of members of Oxynema are cylindrical, narrowed and bent at the ends, commonly attenuated to a terminal elongated, more or less sharply pointed cells without calyptra. Thylakoids in cells are distinctly radially arranged, similarly as in the genera Microcoleus and “Phormidium autumnale”-type. The ecology of all members, which belong potentially to these types, is also similar: all species from this cluster were recorded from halophilic habitats, less frequently from thermal springs and soil biotopes with higher salt contents.

There are no specific studies on freshwater red algae from Italy, and the few existing data are reported in broader studies on algae of rivers. The aim of this paper is to contribute to the knowledge of this algal group in Italy, providing data on their distribution, morphological features and ecology. Samples of Lemanea fluviatilis, L. sudetica and Batrachospermum gelatinosum were collected from 5 stations in the Tiber River basin (Central Italy). The recorded taxa are known as typical elements of European rivers' algal flora, however they were reported in a few times in Italy. Our records, therefore, have widened their geographical distribution. Morever, the finding of L. sudetica was, for the first time, recorded with certainty in rivers of Central Italy.