Data on the Distribution and Ecology of Pistia stratiotes L. (Araceae) in Hungary

Biological invasions by free-floating macrophytes are emerging as a major threat to lowland freshwater systems in Central Europe, particularly where thermally influenced canal networks create novel habitat conditions. Here, we provide the first detailed account of the distribution, habitat characteristics, and reproductive performance of Pistia stratiotes along the Élővíz Canal system near Békés and Békéscsaba (SE Hungary), situated close to the northern margin of the species' European range. In September 2022, we surveyed 71 sampling points along the canal and its tributaries; P. stratiotes was recorded at 35 sites (49.3%; Table 1). Sampling locations where P. stratiotes was not detected are provided in Table S1. Occupied localities were characterised by chemically relatively homogeneous, strongly alkaline waters (pH 9.28-9.69) with low to moderate conductivity and slow flow (0.05-0.32 m s^-1). Drift counts revealed that higher current velocities substantially enhanced downstream transport of rosettes, indicating that flow-mediated dispersal is a key mechanism of spread within the canal network. Of 126 individuals examined, 12.7% were flowering. Reproductive plants had markedly larger leaves and produced significantly more vegetative ramets than non-flowering individuals, suggesting a size-dependent threshold for sexual reproduction coupled with enhanced clonal propagation under favourable conditions. Our findings demonstrate that partially thermally influenced lowland canals can support persistent P. stratiotes populations under temperate climatic conditions and may potentially act as invasion hubs, although this role was not explicitly tested in the present study. These systems, therefore, warrant priority for monitoring and early management interventions.