- Water Cabbage
- Tropical Duckweed
General: Water Lettuce is an herbaceous, evergreen perennial in the Araceae family. In colder climates, it may exist as an annual.
Flowers: Are small, white to pale-green and clustered in the middle of the rosette. Each plant can have several flowers, each of which arises from a separate leaf axil.
Stems: Water Lettuce is a free-floating aquatic plant and does not have a stem. Instead, leaves are gathered in a rosette.
Leaves: Are light green and spatula-shaped with wavy margins. They are longitudinally ribbed and covered in fine whitish hairs, giving them a velvety appearance. Distinctly, the rosette resembles an open head of lettuce (hence its name) and measures about 10cm wide and 6cm tall.
Seeds: Water Lettuce flowers produce green, egg-shaped, many-seeded berries. Seeds are thin, have a wrinkled surface, and are golden-brown when mature.
Roots: Numerous, feathery roots hang below the rosette. They measure 50 – 80cm long.
Longleaf Pondweed (Potamogeton nodosus) is native to British Columbia. Its leaves are flat against the water, elongated, and have a distinct mid-vein. In contrast, Water Lettuce boasts a lettuce-shaped rosette.
Water Hyacinth (Eichhornia crassipes) is an invasive species present in British Columbia. It can be distinguished by its showy purple flowers, bulbous stem, and large kidney-shaped leaves. In comparison, Water Lettuce has inconspicuous white flowers.
Habitat and Origin
Some experts believe that Water Lettuce is native to the southeastern United States, while others think it originates from either Australia, Africa, southern Asia, South America, West Indies or Mexico.
Water Lettuce is highly abundant in tropical regions, as it thrives in warm, nutrient-rich waters and is sensitive to frost. However, mild climates and global warming are making several areas of British Columbia susceptible to Water Lettuce. It inhabits areas that are contaminated with sewage or fertilizers and slow-moving waters such as streams, rivers, lakes, ponds and wet ditches. It can also survive in mud.
Propagation & Vectors of Spread
Water Lettuce is capable of rapid vegetative reproduction, producing clones from stolons (underground stems). However, in colder climates such as British Columbia, its primary mode of reproduction is by seed.
Water Lettuce spreads by ballast water, boats and fishing equipment, and escapes cultivation in water gardens and aquariums. The wind can also disperse seeds.
Ecological, Economic, & Health Impacts
- Dense mats alter the hydrological properties of ecosystems.
- Large infestations may reduce oxygen levels in water and kill aquatic species, such as fish.
- Competes with native aquatic species and blocks sunlight from penetrating the water column.
- Blocks irrigation canals and reservoirs.
- Can clog hydroelectricity turbines and halt energy production.
- Prevent recreational uses of waterways.
What Can I Do?
Water Lettuce is not yet currently found in the Sea to Sky, so PREVENTION is key:
Learn to identify Water Lettuce: use the images presented on this profile page to learn how to identify Water Lettuce.
What to do if you spot it: You can report any Water Lettuce sighting by clicking here.
- Regularly monitor properties for invasive infestations.
- Clean, Drain, Dry all watercraft. Rinse all mud, debris and plant fragments from all equipment, wading gear, and boats.
- Ensure all plant parts are bagged or covered to prevent spread during transport to designated disposal sites.
- Store boats in infested areas; remove plant material from any equipment, boats or clothing used in such areas and wash equipment and boats at designated cleaning sites before leaving infested areas.
- Plant Water Lettuce in an aquarium or water garden, no matter how well-contained its enclosure may seem.
- Compost any parts of the plant. Instead, dispose of Water Lettuce in the general/household waste stream at the landfill as the seeds will be able to persist the composting process.
- Move soil or water that has been contaminated with Water Lettuce.
- Small infestations can be raked or seined, however, control must be repeated over the long term and is likely ineffective for large infestations.
- Harvesters can also remove plants.
- Herbicides cannot be applied in aquatic environments in Canada.
- Herbicide control is not recommended for this species.
- There are currently no biological controls in British Columbia.
- CABI, Pistia stratiotes (Water lettuce), https://www.cabi.org/isc/datasheet/41496
- Fraser Valley Invasive Species Society, Water Lettuce, https://www.fviss.ca/invasive-plant/water-lettuce
- Global Invasives Species Database, Pistia stratiotes, http://www.iucngisd.org/gisd/species.php?sc=285
- Government of Ontario, Water Lettuce, https://www.ontario.ca/page/water-lettuce
- Great Lakes Nonindigenous Species Information System, Pistia stratiotes, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=1099&Potential=Y&Type=2&HUCNumber
- Ontario Invasive Plant Council, Invasive Aquatic Plant Species: A Quick Reference Guide, https://www.ontarioinvasiveplants.ca/wp-content/uploads/2019/04/reducedQuickReferenceGuide_AquaticPlants.pdf