Seasonal development of Conioselinum tataricum Hoffm. ( Apiaceae ) individuals of different age was studied. It was found that a part of individuals had a reduced period of vegetation. The most favourable time for study of coenopopulation age structure is rec-ommended. The best time for measurement of seedlings, juvenile, immature, subsenile and senile individuals is mid-June, immature and subsenile individuals — early July, and virginal and genera-tive ones — the second half of July.Keywords: seasonal development, age stages.