Pistia stratiotes

Pistia stratiotes is a pantropical floating plant of the arum family.¹ The light green, velvety leaves sit without a stalk in a rosette, are obovate to spatulate and strongly veined beneath; long, branched, bluish black roots hang down below.¹ In the tropics and subtropics it not infrequently becomes a nuisance weed, rapidly colonising still and sluggish waters.¹

In nitrate-rich, heavily polluted water rosettes up to 80 cm across are possible; in the aquarium it stays considerably smaller.¹ Warmth and strong light produce sturdier plants, yet low to moderate lighting is sufficient, and both soft and hard water are suitable.¹ Regular thinning is necessary because runners quickly form a dense floating cover; in garden ponds it does not survive the winter.¹ According to a forum discussion from 2024, trade in it is banned in the EU.²