Morphological characteristics and molecular phylogeny of ‘Tateyama‐marimo’ (Cladophorales) from Tateyama Town, Toyama Prefecture, Japan: a comparative study with related freshwater algae

SUMMARY ‘Tateyama‐marimo’ represents a Japanese freshwater alga that is considered to be the same as or closely related to Aegagropilopsis moravica (Cladophorales), which is distributed in the Eurasian Continent. However, morphological and genetic studies on ‘Tateyama‐marimo’ remain limited. This study aimed to elucidate the taxonomic and phylogenetic positions of ‘Tateyama‐marimo’ and Aegagropilopsis moravica based on comparative morphological observations utilizing light and electron microscopy and molecular phylogenetic analysis. The samples were collected from the Tateyama Town, Toyama Prefecture, Japan, where ‘Tateyama‐marimo’ was first recorded. Light microscopy revealed that the morphological characteristics of ‘Tateyama‐marimo’ were generally consistent with those reported for Aegagropilopsis moravica . Transmission electron microscopy of ‘Tateyama‐marimo’ presented a polypyramidal pyrenoid structure surrounded by four or more starch sheaths, indicating the high similarity to the ultrastructure of others of the Cladophorales taxa at the ultrastructure level. Additionally, bilenticular‐ and zonal‐type pyrenoids surrounded by two–three starch sheaths were observed. The 2034 bp nucleotide sequences across 18S and 28S ribosomal DNA exhibited high similarity between ‘Tateyama‐marimo’ and Aegagropilopsis moravica , indicating their monophyletic origin on the molecular phylogenetic tree. Altogether, these results suggested that ‘Tateyama‐marimo’ should not be excluded from being treated as Aegagropilopsis moravica ; nevertheless, further taxonomic scrutiny is warranted.