Abstract
We have determined the timing of periodic events, such as leaf formation, flowering, fruiting and wintering of the aquatic plant Potamogeton alpinus. This study was performed in 15 watercourses situated in NW Poland in 2014–2015. Characteristics of the age stages were determined on the basis of 728 modules and phenological data were collected from permanent plots. In the study area, the plant appeared in week 12 of the calendar year, when water temperature in the streams was 5.4 ± 0.16°C. At that time, the first leafy juvenile shoots developed from winter buds. In week 22 (water temperature 13.9 ± 0.85°C), juvenile shoots became mature, whereas the first flowers were formed in week 24 (15.6 ± 1.04°C). The generative phase lasted twelve weeks with water temperature from 15.6 ± 1.04°C to 18.9 ± 3.23°C. Between weeks 37 and 44 (water temperature from 13.7 ± 0.77°C to 6.3 ± 1.05°C), senile shoots dominated in the population. From week 45 until week 11 of the next year (water temperature < 5.4 ± 0.16°C), the plants were in the winter resting stage. In our view, climate warming might disturb the phenology of P. alpinus, decreasing the probability of sexual reproduction of the species and the phenological distance between the Central European Plain and the Scandinavian populations.