Is Aquatic Fern Salvinia natans (Salviniaceae) Rare in Russia?

Using published and herbarium data, and internet resources, the change in distribution of the aquatic fern Salvinia natans (Salviniaceae) in Russia has been traced since the beginning of 20th century until 2021 and the current boundaries of its range is identified. Among the bioclimatic and temperature indicators that determine the distribution of S. natans, the minimum and maximum temperatures in October and January and the maximum temperatures in April and July show the highest statistical significance, which is associated with important stages of the life cycle of S. natans. A comparison of species localities with climatic and temperature indicators for the time periods of 1960-1969, 2010-2018, and 2011-2021 showed that, by 2021 in the European part, West Siberia, and the Far East, there had been a significant spreading of S. natans to the north (more than 200 km). A notable increase in the number of records of the species has been found since the 2000s in different regions. For example, in Ivanovo oblast from 2018 to 2021, their number has increased more than three times. The expansion of the species occurs against the background of a noticeable increase in average annual temperatures and changes in other bioclimatic indicators. If present temperature trends continue, S. natans will expand its range even further north, east, and west in European Russia and north and west in West Siberia and the Far East. Due to the ongoing expansion of S. natans, the premises for the exclusion of the species from a number of regional Red Data Books is discussed.

Automated summary

Using data from published sources, herbarium collections, and internet resources, researchers have tracked the change in distribution of Salvinia natans in Russia from the early 20th century until 2021. They found that temperature indicators in specific months have the highest statistical significance in determining the fern's distribution. The species has expanded significantly in different regions, and if current temperature trends persist, it is expected to continue expanding further north, east, and west in Russia.