A beautiful useful plant for aquarists and pond-ers, the water lettuce can serve several purposes given moderate lighting, aerial moisture and temperature. For toughness, providing shade, and protection for young Pistia is hard to beat.
Historically, difficulties with water lettuce culture have most to do with low humidity, over-illumination in aquariums and chilling in outdoor settings.
Often paired and compared with water hyacinth (Eichhornia crassipes), water lettuce can also become a floating nuisance, clogging waterways if released to the wild. Do check with your State's wildlife laws concerning possessing these plants; and never place unnatural livestock where it can "get loose".
Classification & Species of Use To Aquarists:
Species name, describer, date: Pistia stratiotes LINNAEUS, 1753 is a member of the monocot Family Araceae, the arums; a group of much importance to aquarists. Other arums of note that you should recognize: Acorus, Agalonema, Anubias, Cryptocoryne, andLagenandra. For terrestrial gardeners the Araceae contain even more ornamental tropicals (Alocasia, Colocasia, Cyrtosperma and more).
Synonyms: Pistia aegyptica, commutata, linguaeformis, var lepieuri, bcordata and spathulata Schleiden; P. aethiopica Fenzl; et alia..
Natural Distribution & Ecology: Most all of the freshwaters of the tropics. Consumed by humans in some!
Physical Description: Water lettuce is unmistakable; it looks like a floating lettuce! Pistia bear a floating rosette of light green, longitudinally grooved leaves that appear overly large, thick and spongy. Touch them; they feel something like velvet. In young plants the leaves are rounded in appearance, older, larger (4-6 inch) leaves are more squarish (spatulate).
On the underside, long white to blackish roots may extend for more than a foot, providing breeding and hiding space.
P. stratiotesis common in ponds worldwide but rarely found in aquariums in the west (compared to Europe). Is this due to a poor understanding of basic living requirements? From what I've seen the primary cause of loss for Pistia in aquariums stems from light burn and dryness. For use indoors, this plant needs to have the water lowered in its tank to provide living space, but a top provided to maintain high humidity. Dry, curling ends of leaves are typically due to low water vapor.
Substrate/Soil: Not important with these plants as they are generally kept as floating forms. In very shallow applications, it may be anchored into a peaty soil for purposes of overwintering.
Light/Lighting (intensity, spectrum, duration):10-25k lumens depending on type, actual nearness to the plants. Less heat-releasing sources, e.g. "standard" fluorescents on the upper end, hot metal halides on the lower. Over-lighted plants commonly appear reddish to yellow to brown. These plants need full-spectrum radiation, but not so much red end that they are burned. A typical 10-12 hr. light cycle suits.
pH, KH, Other Chemical:Prefers slightly acidic waters, 6.5-7.2, moderate hardness, 5-20 KH.
Temperature Range:For folks who only have indoor tanks, it may come as a surprise that water lettuce is more often killed from chilling in ponds than baking in aquariums. This is a tropical and sub-tropical species best kept between 72-78 F.. Periodic bouts into the sixties may not kill water lettuce, but will cause growth checks. It will definitely not survive chilling toward freezing temperatures.
Plant Species Kept With: Stodola states that Pistia may be cultivated with other floating plants like Ceratopteris, Salvinia, Lemna, but I prefer to keep water lettuce with most anything it doesn't have to share the surface with; and that can stand to be shaded from a medium to high extent.
Trimming: Plants should not be allowed to completely crowd the surface; pinch off plantlets or remove individuals to keep them gapped.
Pests, Parasites, Diseases:
Except for "hitchhikers" carried from outside culture, no real serious pathogens for aquariculturists. Brown spots can come about from water spots deposited on Pistias silky trichome covered leaves; take care to not use bubblers or otherwise splashing circulation/filtration with this plant.
Propagation: By seeds or runners.
Sexually, a small greenish spathe develops near the plants middle with a female flower at the lower end and a few male ones near the upper tip.
Asexual plantlets are generated by larger plants via long thin runners. These can be pinched off or allowed to detach on their own.
Seasonally, plants are offered starting around April, May or June grown from seed or green-house grown runners. If you're keeping them outdoors, they are easily over-wintered by removing to an indoor pool or aquarium during colder months and hibernating them in moist sand and peat.
So, water lettuce can be grown indoors! It's a great plant for spawning and rearing livebearers, and easily kept given humidity, moderate temperatures and light.
Brown, Phillip J. 1978. Aquarium plants: Water lettuce. TFH 3/78.
Brunner, Gerhard. 1973. Aquarium Plants. T.F.H. Publications, NJ. 159 pp.
Riehl, Rudiger & Hans A. Baensch. 1987. Aquarium Atlas, v. 1. MERGUS, Germany. 992 pp.
Roe, Colin D. 1967. A Manual of Aquarium Plants. Shirley Aquatics, England. 111 pp.
Stemmermann, Lani. 1981. A Guide to Pacific Wetland Plants. U.S.Army Corps of Engineers, Honolulu. 118 pp.
Stodola, Jiri. 1967. Encyclopedia of Water Plants. T.F.H. Publications, NJ. 368 pp.
An aquarium shot of some 10 cm. Pistia in an aquarium (in Germany).