|A taxonomic review of the genus Phaeocystis|
Medlin, L.; Zingone, A. (2007). A taxonomic review of the genus Phaeocystis, in: Van Leeuwe, M.A. et al. (Ed.) Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements. Biogeochemistry, 83(1-3): pp. 3-18
In: Van Leeuwe, M.A. et al. (Ed.) (2007). Phaeocystis, major link in the biogeochemical cycling of climate-relevant elements. Biogeochemistry, 83(1-3). Springer: Dordrecht. ISBN 978-1-4020-6213-1. 330 pp., more
In: Biogeochemistry. Springer: Dordrecht; Lancaster; Boston. ISSN 0168-2563, more
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VLIZ: Aquatic communities PBC 
Taxonomy; Phaeocystis antarctica Karsten, 1905 [WoRMS]; Phaeocystis cordata A.Zingone & M.J.Chrétiennot-Dinet, 2000 [WoRMS]; Phaeocystis globosa Scherffel, 1899 [WoRMS]; Phaeocystis jahnii A.Zingone, 2000 [WoRMS]; Phaeocystis pouchetii (Hariot) Lagerheim, 1896 [WoRMS]; Marine
Phaeocystis is recognized both as a nuisance and as an ecologically important phytoplankton species. Its polymorphic life cycle with both colonial and flagellated cells causes many taxonomic problems. Sequence variation among 22 isolates representing a global distribution of the genus has been compared using three molecular markers. The ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) spacer is too conserved to resolve species. The most conserved 18S ribosomal deoxyribonucleic acid (rDNA) analysis suggests that an undescribed unicellular Phaeocystis sp. (isolate PLY559) is a sister taxon to the Mediterranean unicellular Phaeocystis jahnii; this clade branched prior to the divergence of all other Phaeocystis species, including the colonial ones. The internal transcribed spacer (ITS) region shows sufficient variation that some spatial population structure can be recovered, at least in P. antarctica. P. globosa and P. pouchetii have multiple different ITS copies, suggestive of cryptic species that are still able to hybridize. A molecular clock has been constructed that estimates the divergence of the cold water colonial forms from the warm-water colonial forms to be about 30 Ma and the divergence of P. antarctica and P. pouchetii to be about 15 Ma. A short description of the colonial stage and the flagellated stage for each formally recognized species is provided. Morphological information is also provided on a number of undescribed species. These include the strain Ply 559, consisting of non-colonial cells with peculiar tubular extrusomes, a second non-colonial species from the north western Mediterranean Sea producing a lot of mucus, and a colonial species with scale-less flagellates found in Italian waters. In addition, three flagellated morphotypes with scales different from those of P. antarctica were reported in the literature from Antarctic waters. The picture emerging from both molecular and morphological data is that the number of species in the genus is still underestimated and that cryptic or pseudocryptic diversity requires a sound assessment in future research of this genus. Based on all published observations, an emended description of the genus is provided.