About Najas marina L.
Najas marina L. is an annual aquatic plant that grows a slender, branching stem reaching a maximum length of 40 to 45 centimeters. Its evenly spaced leaves grow up to 4 centimeters long and 1 to 3 millimeters wide, with fine saw-like teeth along their edges and prickles along the leaf midvein. Very small, stalkless green flowers grow in the axils where leaves attach to the stem. This species is dioecious, meaning male and female flowers develop on separate individual plants. In the British Isles, it is possible that only female plants of this species are found. Najas marina flowers in mid-summer.
Najas marina has a broad, nearly circumglobal distribution across temperate and tropical regions. It grows in mesoeutrophic water, rooted in deep peat or muddy substrate. It was first recorded in the British Isles in 1883 at Hickling Broad, Norfolk, where it had already become established. Populations of the species in this area declined during the 1960s due to pollution. Measures have since been implemented to reduce nutrient levels in the Norfolk Broads, which has led to improved water quality there.
