Water Lettuce (Pistia stratiotes)

Pistia or water lettuce is a monotypical genus of the Araceae family, represented only by a single kind of fluctuant – Pistia stratiotes. This widespread plant can often be encountered in tanks since it looks appealing and not demanding in terms of care. In the article, you will find out about the plant habitat, how to propagate and keep it in a tank properly.

Habitat in the wild

The genus name origins from the Greek’ pistis’, which means ‘water.’ The full Latin name of the plant means ‘water lettuce.’ Among aquarists, it is also known as water lettuce, Nile cabbage, and shellflower.

Really, the upper part of the plant resembles young lettuce crops. In the wild, it is prevalent in South America and Carribians. It is quite probable that South Africa is the plant’s native land. However, currently, it grows worldwide, mainly in the tropics and subtropics, and it is absent only in Antarctica.

In the US, it started to be universal in occurrence from the mid-1700s. Pistia was acknowledged as invasive exotic species in Australia, the USA, Puerto Rico, and South Africa. During the last 20 years, this species was encountered in some European countries.

Propagation in the wild

The plant is a persistent weed. In a short time, it can cover a small water body surface completely. In this case, the pond is doomed. Pistia cover increases the pond water consumption since its transpiration requires an overwhelmingly greater water amount than the one that evaporates from the pond’s free surface.

The cover prevents sunlight from getting inside the pond water this way damaging the development cycle of other plants, and atmospheric oxygen also can’t get there, which causes various aquatic organisms death.

Pistia root system provokes the pond silting and makes the bottom substrate unfit for fish spawning. It creates favorable conditions for mosquitos living, and this way promotes their reproduction.

The plant migrates along large distances also due to birds which carry not only the seeds but also vegetative parts of a plant. In Africa, it migrates together with rivers flow by going large distances together with other plant fragments.

The same way rivers in India and South America carry vegetative parts of a plant. Man has also promoted water lettuce expansion by reproducing it in large amounts as a medical plant and then throwing it away into local ponds.

Like other similar fluctuant, water lettuce has a huge potential for biomass proliferation. Such high productivity and nutritive efficiency of the plant are used for producing methane and forage fodder. However, in the latter case, its use is quite limited because of the plant’s ability to accumulate salt of heavy metals in its tissues.

Due to this quality, the rot-off biomass is sometimes used to remove metal combinations from industrial wastes.

To control the water lettuce amount, first of all, it is gathered employing machines from the water surface and then taken to the dry land. In tropical countries, the greenery gathered like this is used as forage fodder for cows and pigs. Except for the approach mentioned above, chemical and biological approaches are also utilized to control plant propagation.

Description

The leaves form an afloat rosette, and the leaves have intercellular space filled with air. The diameter of such a rosette may be up to 25 cm (10 in) large.

From below, the leaves are silvery-green with excurrent longitudinal veins. They are up to 15 cm (6 in) long and up to 8 cm (3 in) wide. The adult plant’s full length, including the roots, may vary from 15 cm (6 in) to 30 cm (12 in).

The leaves are covered with short grayish filaments protecting them from getting wet, taking on the role of repellent fabric. Due to their sponge structure with air cavities, water lettuce easily floats.

The plant has numerous floating feathery roots. They are light-colored initially and become blueish or even black as they grow, which is normal in this case.

The roots length is up to 20 cm (18 in). As a rule, they in the water, but when the plant gets on shallow water, it can strike roots in the ground. They have a high suction force and can clean water from toxic admixtures, including a salt of heavy metals.

Water lettuce care in aquarium

Water parameters and temperature

Water lettuce is widely distributed in tanks. It grows well at artificial ceiling lights and high air humidity. Provided with proper conditions, the plant can grow all year round. However, in this case, its size is a bit smaller.

It grows well both in soft and hard water. Warm temperature and intensive light are enough to get a good specimen.

Tank water characteristics (hardness and pH) don’t have any significant impact. Water lettuce can grow within a wide range of these: pH 5,9-8,4; GH < 25 °; KH < 1. When water hardness exceeds 12°, it demonstrates a bit poorer growth. When the pH value is less than 5, the plant stops growing, while when the pH value is close to 7, it demonstrates the best growth rate. The favorable tank water temperature range is from 15 to 35 °C (the optimal one is 22-30 °C, 72-86 ºF).

To prevent pistia from interfering with other tank plants’ development, you should control its amount and thin it out from time to time. Removing unwanted some of its amount will not only let you keep the parent plant in good condition (at least for a year) but also will provide a more comfortable light condition for bottom plants.

Lighting

The length of light should be at least 12 hours and preferably not more than 14 hours a day. In insufficient lighting, the pistia grows smaller, and its new leaves do not rise above the water surface. At unfavorable conditions, the leaves lay on the water surface. If the tank conditions are good, they rise above the water.

In tanks, it is often used as a shield to cover the bottom areas where shade-requiring plants grow to protect them from excessive light.

Bottom substrate and root system

The root system may grow underwater up to 30 cm (12 in) deep. Usually, it doesn’t touch the bottom and stays in the water; thus, the bottom substrate composition is not important.

The root system condition shows if all the necessary chemical compounds are present in the water. In water poor in macro-and microelements, the plant root system starts quickly growing in size to the detriment of its above-water part. As a result, you get a small rosette with a branched root system. If water has enough nutrients, such a misbalance won’t occur.

Thus, the over-developed root system indicates a lack of nutrients in the tank water. In this case, you should increase the portion of fertilizers you put in the water or increase the number of fish that are the source of organic fertilizers.

Fertilizers

The plant reaches its maximum size in tank water that is rich with nitrogen compounds. During the active vegetation period, it is recommended to force the plant with compound fertilizers that must contain microelements. The dosage of the fertilizers is approximately the same as for most tank plants.

Seasonal patterns

Water lettuce has a rather obvious active vegetation period. It starts in spring when the daylight period grows, and a large number of new leaves appears. Rosettes quickly become about 10-12 cm (4-5 in) in diameter. When autumn comes, the vegetation pace slows down.

Part of the leaves rot off, and only small leaves remind to overwinter together with the roots. The dormant period lasts about 2-3 months, and then another vegetation period starts.

In a tank, you can ignore this growth cycle by creating artificial conditions for the plant’s active vegetation during the whole year.

Such an activity lasts for several months. During this time, newly appeared plants will grow to become as large as a parent plant. When the rosette becomes 5-6 cm (2 in) large, you can separate the new plant from the parent one.

Benefits of water lettuce in an aquarium

Pisitia in an aquarium is not only a decoration but also a useful plant.

Firstly, it actively consumes organic components dissolved in the water, acting as a kind of biological filter decreasing nitrates and ammonia levels.

Secondly, in the case of salt of heavy metal presence in the water, the plant accumulates them in its tissues, decreasing their amount in the water to safe levels. That’s why this plant is extremely desirable to have in tanks with sensitive fishes, demanding to water chemical composition.

Thirdly, the leaves bottom and thick roots of the plant are perfect spawning substrates for fishes that lay eggs close to the water surface (for example, betta and dwarf gourami).

Finally, these thick roots can be shelter and food for juveniles of many fish species (for example, platies and guppies). Many fishes feeding on aquatic vegetation will eagerly eat the roots as well.

Water lettuce is also welcome in terrariums, especially when keeping red-eared terrapins (that are happy to eat the plants’ roots and leaves) and axolotls (sensitive to water purity).

Propagation in the aquarium

The plant propagates both vegetatively and with its seeds. In a tank, it blooms very seldom; thus, the propagation using the seeds is almost not in common practice. Provided with favorable conditions, it uses a vegetative way for quick propagation by growing stem shoots. The propagation process is extremely fast in warm water at natural lighting. Young shoots can be separated from the parent plant after they have about 2-3 new leaves on them.

In the wild, after the shoots are separated from the parent rosette, they are carried away by the flow or by animals.

Due to its ability of fast vegetative propagation with stem shoots, water lettuce quickly forms a nice green fluctuant cover on the water surface.

Illnesses and infestants

Pistia has native immunity against various illnesses and infestants. Seldom enfeebled or old specimens can be infected with fungi or bacteria. Sometimes aphid may infect the plant. Its leaves are good food for snails; thus, you shouldn’t keep it in a tank with many shellfish.

After getting the plant, you should thoroughly wash the rosette and the roots not to bring any infestants or pathogenic agents.

It is recommended to keep the plant quarantined for at least two weeks and only after putting it into a tank.