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A detailed study of the type specimen of Plocamium cartilagineum and other original material of European species of Plocamium revealed that the nomenclatural reorganization proposed by Saunders & Lehmkuhl in 2005 must be revised. The main consequences of the new interpretation are: (1) the use of Plocamium lyngbyanum to name their molecular entity EUR1 (previously considered to be equivalent to P. cartilagineum s.s.); and (2) adopting P. cartilagineum for their molecular entity EUR2, which renders P. subtile Kutzing a taxonomic synonym. Using a combination of morphological, anatomical and molecular information (barcoding), we conclude that the colour and consistency of the thallus, the number of ramuli per series, the morphology and arrangement of the tetrasporangial stichidia, the length of the tetrasporangia, and the type of habitat are the most reliable characters of classical taxonomy for discriminating between the species of Plocamium occurring in northern Europe.

The Plocamiaceae currently includes two genera: the free-living Plocamium and the adelphoparasite, Plocamiocolax. Plocamium includes ca. 40 species that are widely distributed throughout the world's oceans. Most species are clearly defined anatomically and biogeographically; however, the type species Plocamium cartilagineum (type locality: considered northern Europe) is an exception. Although reportedly cosmopolitan in distribution, our investigations unequivocally indicate that there is substantial genetic diversity among isolates from different geographic locations and that there are at least eight divergent cryptic species currently included in P. cartilagineum. In this investigation we focused on populations of P. cartilagineum from northern Europe. We used a combination of molecular and morphological characters in order to establish boundaries between four cryptic species in this geographical area. Our molecular results not only resolve these four entities as distinct, but also indicate that they are...

Thirteen species from the red algal flora of Helgoland (southern North Sea) were exposed to UVA + UVB radiation for various periods in the laboratory, and dark-adapted variable fluorescence (F v:F m) was measured immediately after the UV treatment and again after various recovery times in white light. With the exception of Porphyra umbilicalis, all species showed a decrease in F v:F m on exposure to UV radiation, followed by recovery towards the initial values during the next 24–48 h in white light. The rate of the initial decrease was greater, and the extent of recovery was less, in deep subtidal species (e.g. Delesseria sanguinea, Plocamium cartilagineum) than in intertidal or shallow subtidal species, although there was no direct correlation between these indicators of sensitivity to UV radiation and the depth range of a species, and only slight differences were detected between populations of a single species collected from different depths. There was also little evidence of a seasonal change in sensi...