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The emergence of plants with red leaves is related to accumulation of permanent anthocyanin pigments. Their temporary production under unfavorable environmental conditions is usually treated as an adaptive trait facilitating thermal stability and resistance to pests and diseases. The main pigment that is produced temporarily in almost all plant species is cyanidin monoglycoside. Using common barberry and its purple-leaf variant as a case study we found out that the predominant pigment in red leaves turns out to be the methylated derivative of cyanidin, namely peonidin-monoglycoside, although that does not alter the qualitative composition of anthocyanin pigments in red and green leaves. Ample accumulation of peonidin in the plants is shown to be inert with regard to basic functional properties: the plants continued to grow and bear fruits, though in different proportions. It is pointed out that more intense illumination leads to changes in energetic state of photosynthetic apparatus which are most prominent in the purple-leaf variant. Judging by the changes in fast fluorescence at different levels of illumination, red leaves at a low level of illumination utilize solar energy less efficiently by comparison with green ones.