Photo Credit: F. Starr & K. Starr, Starr Environmental, Bugwood.org
Management Category
Squamish
Whistler
Pemberton
Vectors of Spread
General
Water Lettuce is a herbaceous, evergreen perennial (present all year) in the Araceae family. The species has been termed the most productive freshwater aquatic plant in the world (hydrophyte).
Synonyms
- Water cabbage
- Tropical duckweed
- Floating aroid
- Nile cabbage
- Pistia
- Shell-flower
ID Characteristics
Flowers: Small, white to pale green flowers clustered in the middle of the rosette. Each plant can have several flowers, each arising from a separate leaf axil.
Stems: As a free-floating aquatic plant, Water Lettuce has no stem. Instead, leaves are gathered in a rosette.
Leaves: Are light green and covered in fine white hairs. The leaves are ribbed length-wise. They rise into the air when healthy and lay flat on the water when growing in poor conditions. Distinctly, the rosette resembles a lettuce head, about 10 cm wide, 20 cm long, and 6 cm tall.
Roots: Numerous feathery roots hang below the rosette. They measure 50 – 80 cm long.
Fruits: Green, egg-shaped, many-seeded berries. Seeds are thin, have a wrinkled surface, and are golden-brown when mature.
Similar Species
Native
Photo Credit: C. Evans, University of Illinois, Bugwood.org
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.
Invasive
Photo Credit: L. Mehrhoff, University of Connecticut, Bugwood.org
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
The origins of Water Lettuce are disputed. Some experts believe that Water Lettuce is native to the southeastern United States, while others think it originates from Australia, Africa, southern Asia, South America, the West Indies or Mexico.
Water Lettuce is abundant in tropical regions, as it thrives in warm, nutrient-rich waters. However, mild climates and global warming are making several areas of British Columbia susceptible to Water Lettuce. It inhabits areas contaminated with sewage or fertilizers and slow-moving waters such as streams, rivers, lakes, ponds and wet ditches. Water Lettuce can also survive in mud and moist air.
How it Spreads
Water Lettuce is capable of rapid vegetative reproduction, producing clones from stolons (underground stems connecting the mother plant to the daughter). 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 the seeds.
Impacts
Ecological:
- Forms dense mats that 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 prevents sunlight from penetrating the water column.
Economic:
- Blocks irrigation canals and reservoirs.
- Can clog hydroelectricity turbines and halt energy production.
- Prevents recreational uses of waterways.
- Interferes with paddy crop production.
Prevent the Spread
Water Lettuce is NOT currently found in the Sea to Sky Corridor, so the best approach to controlling its spread is by PREVENTION.
This is a high-priority invasive species for the Province of BC, and it is included in the Early Detection and Rapid Response (EDRR) program.
If you see Water Lettuce, please report it.
BC Wide Distribution
Water Lettuce Factsheet
Having trouble viewing the factsheet? Don’t worry, all the information is included on this page. You can also contact us with any questions.
References
- Blue Lakes Project, Water Lettuce
- Centre for Agriculture and Bioscience International (CABI), Pistia stratiotes (Water lettuce)
- Fraser Valley Invasive Species Society, Water Lettuce
- Global Invasives Species Database, Pistia stratiotes
- Government of Ontario, Water Lettuce
- Great Lakes Nonindigenous Species Information System, Pistia stratiotes
- Ontario Invasive Plant Council, Invasive Aquatic Plant Species: A Quick Reference Guide