The object of the study is Stellaria humifusa (Caryophyllaceae) – a polycarpic herb with a long taproot; an almost Arctic hygrophyte with circumpolar distribution. Plants form mats and grow on rock outcrops near coastal areas. The plant community consists of only one species, and is covered with a layer of dead leaves from the previous year. The study of lipids showed that during active growth S. humifusa has lipid fractions in the functionally active state. The fraction of neutral lipids (a structural component of the cell and its emergency stores) dominates in terms of the percentage of saturated fatty acids (FA). The fraction of phospholipids (the main membrane system of the cell) has the greatest content of FA with high quantities of diene, triene and saturated FA. This fraction contains the maximum amount of linoleic acid. The fraction of glycolipids (lipids of chloroplast membranes) accounts for around 32 % of the plant’s total FA. It indicates a tense lipid metabolism associated with photosynthetic activity. This fraction contains less of diene and saturated FA, but significantly more of triene FA, including linolenic acid, comparing to the other groups The study of AOS activity in S. humifusa leaves revealed relatively lowperoxidase activity (2.2 and 1 μmol TG/mg protein at pH 5 and 7.8, respectively) simultaneously with high catalase activity (366 μmol H2O2/mg protein) as compared to other herbaceous plants. This fact possibly indicates the species is adapted to the environment. The high level of unsaturation of the lipid structure of the photosynthetic apparatus membrane system contributes a lot to the maintenance of its high functional activity in S. humifusa.