This member of the Isoetaceae family was given this name by Carl Linnaeus in 1753. It is found from Canada, through Europe to northern Asia, growing in lakes with little nutrition from five centimetres to five meters debt. The caudex can grow to one and a half centimetre, the leaves to 40 centimetres length.
The genera name means 'all the same year round'. The species name; lacustris, from the Latin lacus; 'lake', and ustris; 'origin'. Also seen as member of the Juncaceae and Lycopodiaceae families.

