The water chestnut (Trapa natans L., Lythraceae) in Irkutsk region

Trapa natans s.l. is a species included in Red Books of all regions of the Baikal Siberia. From Irkutsk Region, this species is known only from the Solonetskoye Lake (Taishetskii Raion). Traditionally, plants from this lake attributed to the small species T. sibirica Flerow, however no special studied have been conducted. Basing on original data from 2017 and earlier observations, we have confirmed that the water chestnut from Solonteskoye lake belong to T. sibirica. Besides, we characterize the population dynamics of the species, i.e. we note the disappearance of communities with dominance of T. sibirica, and continuous decline of the species abundance. We stress that there is a danger of extinction of the water chestnut from the Solonetskoye lake and accordingly from flora of the Irkutsk Region.