The 18S rRNA phylogenetic tree of pennate diatoms. The 18S rRNA phylogenetic tree inferred by FastTree approximate-maximum-likelihood for pennate diatom strains obtained during the Green Edge campaign (in bold), using an alignment of 49 sequences with 436 nucleotide positions. Circles mark strains retrieved from the Ice Camp sea ice (open) and water samples (solid); triangles (solid) mark Amundsen cruise water samples. The origin, sampling substrate, and phase of the bloom from which they were recovered are provided along with their names and RCC code in Supplementary Data S1. When one phylotype is represented by more than one strain, the number of strains is indicated between parenthesis. For the reference sequences, the strain (whenever available) and the Genbank ID number are displayed. Environmental sequences are marked in blue. DOI: https://doi.org/10.1525/elementa.401.f4