A perennial herb found mainly on peaty, acidic substrates in, or on the margins of, slow-flowing streams, ditches, pools and the sheltered shores of some larger lakes and tarns, often in seasonally flooded sites. It also occurs in muddy hollows in grasslands and heaths, and the wet floors of disused quarries, sand- and gravel-pits. 0-435 m (Llyn Gwngu, Cards., and Styhead Tarn, Cumberland).
Many of the losses of E. fluitans occurred before 1930, following drainage or the loss of lowland heathland, and this decline has continued in England since the 1962 Atlas. It is better recorded now elsewhere.
Oceanic Southern-temperate element, with a disjunct distribution.
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