Easily confused with : other 'Waterweeds' belonging to differing genera.

It is not native to the UK (just to Brazil, Uruguay and Argentina) and occurs sporadically in the UK mainly in canals as throw-outs from garden ponds. It is a dioecious plant with male and female flowers on separate plants. But because only the male was imported, it does not spread by sexual means, but rather vegetatively. It is not as much a problem in the wild within the UK as many other 'waterweeds'. This is the only species of Egeria in the UK, but there exist 2 other species in the rest of the World. Other more vigorous 'Waterweeds' belong to differing genera: Elodea, Hydrilla and Lagarosiphon.

Large-flowered Waterweed does not flower often in the UK, and only when the water is warm. When growing, mainly in Central and Southern Britain and some canals and mill ponds in South Lancashire. Grows in shallow water from the bottom, and when it reaches the surface spreads horizontally into a thick floating raft blocking out the light to other species and aquatic life. It's only saving grace is that it is reported to produce some antibiotics which inhibit the growth of toxic blue-green algae.

The stems are up to 2m long whilst the leaves 10-30mm long, 1.5-4mm wide with an acute apex.