Aquatic plant facts for kids

The beautiful flower of a water lily

A bud of the lotus plant, which grows in water

Aquatic plants, also called hydrophytes, are amazing plants that have learned to live in water. You can find them in both salty ocean water and fresh water like lakes and rivers. These plants are super important for water environments.

In places like lakes, rivers, and wetlands, aquatic plants offer shelter for aquatic animals such as fish and amphibians. They also make oxygen through photosynthesis, which all water creatures need to breathe. Many animals also eat these plants. Some common aquatic plants you might know are water lilies, lotuses, duckweeds, and water hyacinths.

Living in water means these plants need special features. They often have light, spongy cells inside them, called aerenchyma, which help them float. Many also have leaves that float on the surface or are very finely divided. Aquatic plants only grow well in water or in very wet soil, so they are often found in swamps and marshlands.

How Aquatic Plants Evolved
How Aquatic Plants Look and Grow
Types of Aquatic Plants
- Macrophytes: Plants You Can See
- Microphytes: Tiny Water Plants
Special Adaptations for Water Life
Why Aquatic Plants are Important
- Uses for Humans
Where Aquatic Plants Live
Invasive Aquatic Plants
Nutrient Pollution and Eutrophication
Climate Change and Aquatic Plants
Habitat Degradation
Gallery
See also

How Aquatic Plants Evolved

Aquatic plants didn't all start in the water. Many different types of plants, like ferns and flowering plants (called angiosperms), have evolved over time to live in water. This happened many times in different plant families.

For example, seagrasses are special flowering plants that can live completely underwater in salty ocean water. Scientists think that some of the very first flowering plants might have even started in water a long, long time ago. One of the oldest known flowering plant fossils, called Archaefructus, is about 125 million years old and was an aquatic plant!

How Aquatic Plants Look and Grow

Plants that live completely underwater don't need strong, woody stems like land plants. The water helps hold them up! They often have special air-filled spaces inside, which help them float. If you take these plants out of the water, they usually become very floppy.

However, plants in fast-flowing rivers need to be strong enough not to break or get pulled up by the current. They have special tissues to help them stay anchored.

Many underwater plants have very thin, feathery leaves. This shape helps them move easily in the water. It also gives them a larger surface area to absorb nutrients and gases from the water. Some plants, like the Ranunculus aquatilis (water buttercup), can even grow two different kinds of leaves! They have fan-like leaves underwater and flat, lobed leaves that float on the surface.

Some plants, like the water soldier, can even move up and down in the water. They rest at the bottom in winter. Then, in spring, they slowly float to the surface to flower. After flowering, they sink back down.

Plants with leaves floating on the surface have tiny pores, called stomata, only on their top side. This lets them take in carbon dioxide from the air. Since they are in water, they don't worry about drying out, so these pores stay open. Some aquatic plants can even use a different form of carbon, called bicarbonate, from the water for photosynthesis.

Types of Aquatic Plants

Scientists group aquatic plants into different types based on how they grow.

Macrophytes: Plants You Can See

Macrophytes are aquatic plants that are big enough to see without a microscope. They can be divided into four main groups:

Emergent Plants: These plants grow in water but stick out into the air. Think of reeds or cattails (Typha). Their leaves and flowers are above the water, which helps them get sunlight and be pollinated by wind or insects.
Submerged Plants: These plants live completely underwater. Some are rooted to the bottom, like Myriophyllum spicatum. Others float freely without roots, such as Ceratophyllum demersum.
Floating-Leaved Plants: These plants have roots in the bottom, but their leaves float on the water's surface. Water lilies are a perfect example of this type.
Free-Floating Plants: These plants float freely on the water's surface and are not attached to the bottom. Examples include duckweed (Lemna) and water lettuce (Pistia). They can be easily moved by wind.

Microphytes: Tiny Water Plants

Microphytes are aquatic plants that are too small to see without a microscope. They include:

Phytoplankton: These are tiny algae that float freely in the water, drifting with the currents. They are a very important food source for many small water creatures.
Periphyton: These microphytes grow on the surface of other rooted aquatic plants.
Benthic Algae: These algae live on the bottom of freshwater bodies, attached to mud, stones, or other stable surfaces. They can be single-celled or multi-celled.

Many liverworts grow either submerged or on land.

Ceratophyllum submersum, a free-floating plant that grows completely submerged

Eriocaulon aquaticum, an isoetid example, grows submerged in water.

Duckweeds (by size): greater duckweed, common duckweed and rootless duckweed

Lysichiton americanus grows rooted in the bottom with leaves and flowers above the waterline.

Water lilies grow rooted in the bottom with leaves that float on the water surface.

Pistia stratiotes, an example of a neuston, a plant that floats freely on the water surface

Special Adaptations for Water Life

Land Plants in Water

Sometimes, land plants get flooded. When this happens, they can change! New leaves that grow underwater might be thinner than the ones that grew in the air. This ability to change to fit a new environment is called phenotypic plasticity. However, even if a land plant can survive underwater for a while, it might not be able to make seeds if it usually relies on pollinators like bees.

How Aquatic Plants Float

Water helps aquatic plants stay upright because of something called buoyancy. This means they don't need super strong, stiff cell walls like land plants do to fight gravity. In fact, green algae, which are thought to be ancestors of both land and water plants, have very thin cell walls. Land plants developed rigid cell walls to stand tall and survive harsh weather.

Photosynthesis Underwater

Underwater plants face challenges getting enough carbon dioxide for photosynthesis. Light also gets weaker the deeper you go. To solve the carbon problem, many aquatic plants have learned to use bicarbonate from the water as a carbon source. This is a special trick land plants don't have!

Reproduction of Aquatic Plants

Most aquatic flowering plants can make flowers and seeds, just like land plants. But many have also developed amazing ways to reproduce without seeds. They can grow new plants from their rhizomes (underground stems), special buds called turions, or even from broken pieces of themselves. This helps them spread quickly in their watery homes.

Why Aquatic Plants are Important

Aquatic plants play many vital roles in water environments and are useful to humans too.

The Bolivian waterlily holds the Guinness World Record for the largest undivided leaf, measuring about 3.2 meters (over 10 feet) across! The smallest aquatic plant is the rootless duckweed, which is only about 1 millimeter wide.

Many small animals use aquatic plants like duckweeds and lily pads as safe places to lay their eggs. They also use them as hiding spots from predators both above and below the water.

Aquatic plants are the base of the food web for many water animals. They also help keep water clean by soaking up extra nutrients like nitrogen and phosphorus. This helps prevent too much algae from growing, which can harm other water life. Their leaves and roots slow down water flow, trapping sediments and pollutants. Some even have tiny helpers, called microbes, on their roots that can break down pollutants.

Uses for Humans

Food: Many aquatic plants are eaten by people. Examples include wild rice, water caltrop, Indian lotus, and watercress.
Water Health Check: If a lot of aquatic plants disappear from a lake, it can be a sign that the water quality is bad. They are like natural indicators of how healthy the water is.
Medicine: Some aquatic plants, like Centella asiatica and Nelumbo nucifera, are being studied for their potential to provide natural products that could be useful in medicine, for example, to fight cancer.
Wastewater Treatment: Aquatic plants are used in special man-made wetlands to help clean polluted water. They absorb harmful substances, making the water safer.

Where Aquatic Plants Live

The most important thing for aquatic plants is having enough water. But other things also affect where they can grow. These include how many nutrients are in the water, how much carbon dioxide and oxygen are available, the water temperature, what the bottom of the water body is made of, how clear the water is, how fast the water moves, and how salty it is. Some aquatic plants can even live in salty or brackish water.

Invasive Aquatic Plants

Sometimes, plants from one part of the world are brought to a new place. If they grow too well and take over, they are called invasive. These plants can harm the local environment by pushing out native plants and animals.

A common example is water hyacinth (Eichhornia crassipes), which has become a big problem in many warm parts of the world, including parts of the US, Asia, and Australia. Another is New Zealand stonecrop (Crassula helmsii), which can quickly fill up ponds in cooler climates.

Many of these invasive plants were originally sold for aquariums or garden ponds. When people get rid of them by dumping them into natural waters, they can spread and cause serious damage. In 2012, a study found 96 different invasive aquatic plant species in Europe, mostly from North America, Asia, and South America.

Nutrient Pollution and Eutrophication

When too many nutrients, like nitrogen and phosphorus from farms or sewage, get into water bodies, it causes a problem called eutrophication. This leads to huge growths of algae, called algal blooms. These blooms block sunlight, which harms underwater plants. They also use up a lot of oxygen when they die and decompose, creating "dead zones" where fish and other aquatic life cannot survive.

Climate Change and Aquatic Plants

Climate change makes things harder for aquatic plants. Rising temperatures can help invasive species grow faster and outcompete native plants. For example, scientists predict that invasive plants like Egeria densa and Myriophyllum aquaticum might spread even more by 2070 due to warmer conditions.

Changes in weather patterns, like droughts or very heavy storms, also affect water levels and flow. Droughts mean less water, while storms can bring more dirt and pollution into the water. Both of these can be very bad for aquatic plants.

Habitat Degradation

Human activities also damage the places where aquatic plants live. Building cities and farms can lead to more polluted water flowing into lakes and rivers. This pollution can smother plants and change the water chemistry. Farming also adds nutrients and pesticides, which stress aquatic plants.

Building dams and changing how water flows in rivers can also disrupt the natural cycles of aquatic plants and the animals that rely on them.

Aquatic plants are essential for healthy water ecosystems. But they face many threats from invasive species, pollution, climate change, and habitat loss. To protect them, we need to control invasive plants, reduce pollution, fight climate change, and restore their natural homes.