Salvinia natans (Salviniaceae, Polypodiopsida) is a warm-temperate presumably relict fern species that is currently protected not only at the national level in Ukraine, but also internationally in some other countries. It was included in all three editions of the Red Data Book of Ukraine (1980, 1996, 2009), as well as in Appendix I of the Bern Convention, the European Red List (as Near Threatened), and the IUCN Red List of Threatened Species (as Least Concern). An updated analysis of the distribution patterns of S. natans within the territory of Ukraine is provided based on the original research and observations of the authors, herbarium specimens from 37 Ukrainian, Austrian, Czech, Romanian and Russian herbaria, and available literature. As a result, more than 400 localities of this aquatic fern were registered in almost all administrative regions of the country, except Chernivtsi Region and the Autonomous Republic of Crimea. Based on the results of the comparative chorological analysis and the study of the spatial distribution of these localities, it is concluded that the geographic range of S. natans within Ukraine is currently expanding. The studied species in many localities forms large and stable populations, often occupying large areas (over 1 ha) with numerous individuals and projective cover of up to 100% (completely covering the water surface). Due to the active expansion of S. natans throughout Ukraine, the presence of numerous stable populations and over-reproduction of this fern in many regions, it is proposed to exclude (delist) this species from the Red Data Book of Ukraine. However, the need to protect individual natural habitats of the species in the territories included in the Emerald Network and/or in protected areas of the nature reserve fund is emphasized. Populations of S. natans should also be protected at the regional level in geographic regions where the species is infrequent and does not show the expansion trend. In other regions where this fern is excessively abundant, biomass extraction and utilization measures should be developed and implemented.
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