Isoetes lacustris

Tracheophyta LycopodiopsidaIsoetaceaeIsoetesIsoetes lacustris


A submerged aquatic perennial found in oligotrophic lakes with a rocky or skeletal substrate. It frequently forms extensive lawns of many square metres at depths up to 2.5 m and rarely deeper (6 m in Loch Lundie, Westerness). I. lacustris also occasionally colonises artificial reservoirs. 0-850 m (Carn nam Sac, S. Aberdeen).



World Distribution

Eurosiberian Boreal-montane element; also in N. America.

Broad Habitats

Standing water and canals

Light (Ellenberg): 7

Moisture (Ellenberg): 12

Reaction (Ellenberg): 4

Nitrogen (Ellenberg): 1

Salt Tolerance (Ellenberg): 0

January Mean Temperature (Celsius): 2.8

July Mean Temperature (Celsius): 12.9

Annual Precipitation (mm): 1660

Length: 25

Perennation - primary


Life Form - primary

Perennial hydrophyte (perennial water plant)



Clonality - primary

Little or no vegetative spread

Count of 10km squares in Great Britain: 522

Count of 10km squares in Ireland: 147

Count of 10km squares in the Channel Isles: 0

Atlas Change Index: 0.95

Weighted Changed Factor: -9

Weighted Change Factor Confidence (90%)


JNCC Designations


Atlas text references

Atlas (2c)
Hultén E, Fries M
1986.  Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
Jalas & Suominen (1972)
Bangerter EB, Cannon JFM, Jermy AC
1978.  Ferns and their allies. The Island of Mull: a survey of its flora and environment. :12.1-12.7.
Meusel H, Jäger E, Weinert E
1965.  Vergleichende Chorologie der zentraleuropäischen Flora. Volume 1. 2 vols.
Page CN
1997.  The ferns of Britain and Ireland, edn 2.
Preston CD, Croft JM
1997.  Aquatic plants in Britain and Ireland.