Abstract <p>Representatives of the genus <i>Frondicularia</i> (Foraminifera) from the Middle–Upper Triassic deposits of the north of Middle Siberia and Kotelny Island are systematically studied. A complete description of one new species (<i>Frondicularia arctica</i> sp. nov.) and a brief description of seven previously known species are presented. The morphological variability of the studied species is assessed using mathematical methods such as regression analysis, parametric statistical methods and multivariate analysis (principal component method). The observed evolutionary changes in the morphology of the initial part of the shell, and the form of the proloculus from oval to fusiform in three species allowed their assignment to the same phylogenetic lineage (<i>F. lepidaeformis</i> Yadrenkin–<i>F. foliacea</i> Yadrenkin–<i>F.</i> <i>phyllodeaeformis</i> Yadrenkin).</p>