Gymnospermium odessanum is a rare relict endemic plant species. The research was carried out during G. odessanum flowering in 2019–2021 at the botanical-geographical plot "Steppes of Ukraine" of the M.M. Gryshko National Botanical Garden, National Academy of Sciences of Ukraine (NBG). Ecological and coenotic conditions of introduction at the NBG differ from natural habitats of the species and are not optimal for its vegetation. However, this species demonstrated ecological-coenotic plasticity

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... d, over the decades, has formed a stable homeostatic introduction coenopopulation here. As of 2021, the area of introduction coenopopulation of G. odessanum at the NBG was 2,075 m2. It comprises 412 individuals of this species (including 40 seedlings, 241 juvenile, 45 immature, 40 virginal, 45 generative, and 1 sub-senile plants). Coenopopulation fragments with a high density of G. odessanum individuals are rare here, so the average density is low – only 0.2 individuals per 1 m2. In 2021, in the spectrum of age states, the total percentage of pregenerative individuals was very high and reached 88.8 %; the share of generative individuals was 10.9 %.In general, the age structure of the introduction coenopopulation of G. odessanum is characterized by long-term (2010–2021) stability. The spatial distribution of individuals in the introduction coenopopulation is of two kinds – random and in groups. This is due to combined myrmecochoric and barochoric propagation. Also due to myrmecochory, this coenopopulation tends to spread the area. Compared to natural coenopopulations, the introduction coenopopulation of G. odessanum at the NBG is characterized by a larger area, a much significant number, and, at the same time, a low average density of individuals. However, like in most of natural populations, its age spectrum is left-sided.The conducted research testifies the successful formation of the introduction coenopopulation of G. odessanum in the meadow-steppe cultural phytocoenosis of the NBG. This introduction coenopopulation is an example of a successful multi-year scientific experiment and effective ex situ protection and preservation of G. odessanum on the northern border of the Right Bank Forest-Steppe of Ukraine, far beyond the natural range of this endemic plant species.