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The cosmopolitan genus Ceramium Roth (Ceramiaceae), with over 200 currently accepted species, is one of the largest in the Rhodophyta. The genus is characterized by cylindrical or slightly compressed thalli, with axial cells incompletely to completely covered by cortical cells, alternate to pseudo-dichotomous branching and straight to inrolled apices. Despite recent studies, the nomenclature and taxonomy of this genus are still very problematic, linked to the high degree of variation in morphological characters, small thallus sizes, epiphytic habit and the existence of cryptic species. The Mediterranean Sea is reported to have a particularly high diversity of Ceramium species: the North Adriatic Sea, in particular Venice and nearby coasts, was a favourite classical collecting area from where several species were described. In this study we characterize Ceramium sampled from transitional waters of the Venice Lagoon (Italy) by molecular and morphological approaches. Through phylogenetic analyses, using the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) as molecular marker, we identify six distinct taxonomic entities, of which four represent taxa not currently recognized in the Venice Lagoon or the wider Mediterranean Sea. One of these is the poorly known species Ceramium connivens Zanardini, which is non-spiny and fully corticated when mature with short naked internodes developing in older axes. Two entities with erect partially corticated thalli without spines, probably misidentified up to now as Ceramium diaphanum (Lightfoot) Roth, correspond to the new species Ceramium rothianum Wolf et al. and to the forgotten species Ceramium nodosum (Kützing) A.W. Griffiths & Harvey. The last entity, characterized by prostrate axes giving rise to narrow erect incompletely corticated, non-spiny axes, is identified as the rare, poorly known species Ceramium incospicuum Zanardini. [ABSTRACT FROM AUTHOR]

We characterized a new Gracilaria species from the Venice Lagoon, Italy, using molecular analyses based on the plastid large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) and the intergenic RuBisCO spacer (rbcL-rbcS), combined with morphology data. This new entity was recorded on the artificial substrata of the Venice Gulf from March to July, adding to 12 Gracilaria taxa already recorded in the Mediterranean and Adriatic seas. Thalli exhibited a green-yellowish pigmentation with pink shades, and there was dense branching in the distal portions. Tetrasporangia were scattered on thallus cortex and distributed mostly on short, stipitate branchlets. The inner pericarp was connected to the gonimoblast by tubular nutritive cells. The male gametophytic plants formed round-elliptical spermatangial verrucosa-type conceptacles. This species grew attached on artificial rocky substrata of the low midlittoral and upper sublittoral zone in spring and early summer. Molecular analyses based on the plastid-encoded rbcL gene showed a 99.66% nucleotide identity with another Gracilaria sp. from southern Sicily. We compared our rbcL-rbcS spacer sequences with those of two cryptic species, and the phylogenetic analyses confirmed that the Venice populations were a new species. We suggested that the discovery of this new species was not due to an extra-Mediterranean introduction but the consequence of its misidentification as Gracilaria gracilis, which has a similar gross morphology. [ABSTRACT FROM AUTHOR]

The cosmopolitan genus Ceramium (Ceramiaceae, Rhodophyta) is a large and systematically complex group. The taxonomy of this genus remains in a chaotic state due to the high degree of morphological variation. Culture studies, suggesting a strong influence of environment on phenotype, and the use of molecular tools have recently questioned the validity of morphological features used in species recognition. Here we compare three Ceramium taxa from Venice lagoon with samples from northwest Europe using the plastid ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) and the rbcL-rbcS intergenic spacer combined with morphological observations. A strongly banded species, previously identified as member of a poorly understood and misnamed group, the Ceramium diaphanum complex sensu Feldmann-Mazoyer, is probably conspecific with British samples of Ceramium diaphanum sensu Harvey, for which no valid name has been identified up to now. We show thatCeramium polyceras (Kützing) Zanardini is a valid name for this species. A fully corticatedCeramium species morphologically resembling C. secundatum differs at the species level from Atlantic C. secundatum; a valid name for this entity is Ceramium derbesii Solier ex Kützing, described from Mediterranean France. A third species characterized by cortical spines, previously listed as Ceramium ciliatum var. robustum (J. Agardh) Mazoyer, is shown to be Ceramium nudiusculum (Kützing) Rabenhorst, originally described from Venice. [ABSTRACT FROM AUTHOR]