In 2020–2022, the complete taxonomic composition of the flora for the botanical-geographical plot “Steppes of Ukraine” at the M.M. Gryshko National Botanical Garden of the NAS of Ukraine (NBG) was studied and analyzed. This plot was established at the NBG in 1949 to demonstrate the floristic diversity of the Ukrainian Steppes ex situ. According to the inventory results, 347 species and infraspecific taxa from 196 genera and 53 families of higher vascular plants were recorded in the flora of the plot. The steppic component of this plot joins 213 species and infraspecific taxa (61.38 % of the total number of inventoried taxa) belonging to the collection fund and representing the flora of the Steppes of Ukraine, 126 species and infraspecific taxa (36.31 %) of which are introduced plants and 87 species and infraspecific taxa (25.07 %) are native plants. During the inventory, spontaneously growing plants that are not a part of the collection fund were precisely studied. Among inventoried plants, native non-steppic plants are represented by 46 species and infraspecific taxa (13.26 %); alien plants – by 88 taxa (25.36 %), including ergasiophygophytes (45 taxa, 12.97 %) and xenophytes (43 taxa, 12.39 %). The plants of the collection fund predominate on the plot and form the main vegetation cover.Currently, the taxonomic composition of the plot is similar to the characteristics of regional meadow-steppes. The perennials dominate in the biomorphological structure of the plot’s flora (63.69 %), which is typical for the steppic phytocoenoses. In general, a significant number of trees is present here (5.48 %), which is explained by the forest communities surrounding the plot and, as a result, their active self-sowing. Hemicryptophytes prevail in the plot’s flora (60.52 %). Nevertheless, the collection fund of the plot is distinguished by the absence of trees, a greater number of perennials (79.34 %), and hemicryptophytes (72.77 %). The steppic (33.33 %) and marginal (33.33 %) plants prevail in the collection fund, while the amount of meadow plants (18.78 %) is still significant. In the plot “Steppes of Ukraine”, most of the rare introduced plants formed stable homeostatic introduction coenopopulations. Among them, 15 species and rare infraspecific taxa are listed in the Red Book of Ukraine.
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 and, 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.
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