Water Lettuce

Water Lettuce

Pistia stratiotes 
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Water Lettuce, Credit: F. Starr & K. Starr, Starr Environmental, Bugwood.org

Status in Squamish:

PREVENTION-WATCHLIST

Status in Whistler:

PREVENTION-WATCHLIST

Status in Pemberton:

PREVENTION-WATCHLIST
Vectors of Spread:
Water-Lettuce-Vector-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 Lettuce is also known as:

  • 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:
Longleaf Pondweed, C. Evans, University of Illinois, Bugwood.org

Longleaf Pondweed, 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:
Water Hyacinth, Credit: Wilfredo Robles, Mississippi State University, Bugwood.org

Water Hyacinth, photo credit: W. Robles, Mississippi State University, 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.

Report

Please report any sighting of Water Lettuce by clicking here.

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.

Current Distribution

Propagation & Vectors of Spread

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.

Ecological & Economic 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.
What Can I Do?

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.

References