A rhizomatous perennial found in standing or slowly flowing water in sheltered lakes and reservoirs, ponds, rivers, canals, ditches and flooded mineral workings. It favours mesotrophic to eutrophic water and tolerates slightly brackish conditions. 0-320 m (Stony Middleton, Derbys.).
P. pusillus and P. berchtoldii were confused in our area until 1938. Any assessment of changes in their distribution must therefore be based on very limited evidence, especially as they may still be under-recorded. However, comparison of pre-1930 and recent records suggests that P. pusillus may have increased in some areas, perhaps in response to eutrophication.
Circumpolar Southern-temperate element.