Water Lettuce Identification & Treatment
Scientific Name: Pistia stratiotes Category: Floating Tier: 2 — Regionally Significant — Common in multiple EPA ecoregions
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Identification
Water lettuce is a free-floating plant forming rosettes of thick, velvety, light green leaves that look like small heads of lettuce floating on the water. Leaves are 2–6 inches long, wedge-shaped with rounded tips, and have prominent parallel veins. Dense, feathery roots dangle beneath the rosette. Key distinguishing features:
- Rosette of thick, velvety, light green leaves
- Looks like a floating head of lettuce
- Prominent parallel veins on leaves
- Dense white root mass beneath plant
Commonly confused with: Water hyacinth (smooth, glossy leaves with bulbous petioles vs. velvety textured leaves), frog's-bit (smaller, heart-shaped leaves)
Treatment
Recommended Natural Waterscapes Products:
- Harvester (diquat) — Contact herbicide applied directly to foliage. Harvester
- Propeller (flumioxazin) — Contact herbicide effective on floating plants. Check water pH. Propeller
Non-chemical: Physical removal is effective for small infestations.
Regional Note: Like water hyacinth, water lettuce is winter-hardy only in USDA Zones 9–11. In northern areas it is killed by frost and generally not a recurring concern unless reintroduced from water gardens.
Full Profile
- Native Range: Disputed — possibly South America, Africa, or Southeast Asia
- US Distribution: Southeastern US, Gulf Coast, southern California. EPA Ecoregions: Southern Coastal Plain, Southeastern Plains, Mississippi Alluvial Plain. USDA Zones 9–11 (persistent); appears in Zones 7–8 as a seasonal water garden escapee.
- Regulatory Status: Federal Noxious Weed (USDA APHIS). Prohibited in many states.
- Habitat: Still or slow freshwater — ponds, lakes, canals, ditches. Full sun, warm water, high nutrients.
- Reproduction: Vegetative stolons and seed. Rapid reproduction in warm conditions.
- Ecological Benefits: Root masses provide habitat for invertebrates and small fish. Shading reduces algae growth. However, dense mats deplete oxygen, block light, and degrade habitat.
- Seasonal Behavior: Year-round in frost-free areas. Killed by freezing temperatures.
Sources: Texas A&M AquaPlant – Water Lettuce | USDA APHIS Federal Noxious Weed List
Related Species
- Duckweed (Lemna minor and related species (L. gibba, L. turionifera, Spirodela polyrhiza)) — Floating, Tier 1
- Watermeal (Wolffia spp. (W. columbiana, W. brasiliensis)) — Floating, Tier 1
- Water Hyacinth (Eichhornia crassipes) — Floating, Tier 1
- Giant Salvinia (Salvinia molesta) — Floating, Tier 2
- European Frog's-bit (Hydrocharis morsus-ranae) — Floating, Tier 3
- Mosquito Fern (Azolla) (Azolla spp.) — Floating, Tier 3
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