Abstract
Pistia stratiotes L. and Pontederia crassipes Mart. are alien species used in aquarism and aquaculture with a high invasive capacity. The aim of the study was to establish phytocenotic and ecological features of populations of these species in urban river ecosystems. The research was conducted in 2014–2023 on water bodies of the Kharkiv city, Ukraine. Local populations of these species were found in three rivers and vegetation relevés were carried out according to standard phytosociological methods. Alien species occurred with high constancy in the communities of Lemnetea O. de Bolòs et Masclans 1955 and with a minor occurrence in fragments of communities of Phragmito-Magnocaricetea Klika in Klika et Novák 1941. The obtained results of phytoindication show a variability of humidity, aeration, and thermal regime in which the populations of these species occur. The environmental characteristics such as low temperatures, light, salt and nitrogen regime are limiting for occurrence of populations. Climatic and hydrological conditions of the city’s river ecosystems of the city are favorable for spread of communities with the present Pistia stratiotes L. and Pontederia crassipes Mart.