Plant Adaptations to Environments with Abundant Water

Rainforests

Rainforests are warm, wet tropical environments where it rains nearly year-round, so plants can easily access all the water they need. These regions can receive more than 150 inches (400 cm) of rain annually, and their day length and temperatures are consistent throughout the year.

Although there are challenges to surviving in rainforests, they are relatively stable biomes that are generally free of fire, floods, and extremes in temperature and rainfall. These conditions support a lush diversity of life. Vines cover tall trees and huge leaves abound. More species grow in rainforests than in all other habitats combined. Covering just 2% of the earth’s surface, these tropical regions need protection from exploitation.

Layers of a Rainforest

Different layers of a rainforest receive varying amounts of sunlight, from the forest floor (the shadiest) to the emergent layer (the sunniest). Plants are adapted to the conditions in each layer.

Shady below, sunny on top.

• The emergent layer is made up of the tallest trees that stick out or “emerge” from the forest and receive the most sunlight.
• The canopy is made up of the tops of most of the tall trees. It forms a roof over the rest of the forest. It’s a prime area for vines and epiphytes, plants that grow on other plants to reach more light.
• The understory contains smaller tree species, young trees, and vines stretching toward the sun.
• The forest floor is the lowest layer. It receives the least sunlight, so many plants here have large or dark-pigmented leaves to absorb as much light as possible.

Rainforest Adaptations 

Adaptations are changes in lifeforms over time that improve their potential to survive. 

Plants in rainforests have adaptations that help them thrive in moist environments with varying light levels and hungry herbivores. Many plants have similar adaptations that serve different functions in different environments.

• Large, dark leaves are adaptations to low light and ample water. In tropical areas, limited sunlight reaches the forest floor through the many layers of foliage above it, so leaves grow large, dark green, and angled to capture any rays of light filtering through the thick canopy. Dark pigment helps them absorb as much light as possible. 

• Some tropical plants produce new growth that is differently colored from the mature foliage. In this early stage of development, tender new leaves may have a drooping posture that helps avoid sunburn and they may be pale or brightly colored. This coloration may make them “invisible” to herbivores that cannot perceive specific colors or serve as a warning that the leaves taste bad or are toxic.

• Colorful and patterned leaves in a sea of dark-green leaves may protect plants from being eaten by hungry herbivores. Bright colors and patterns make it difficult for animals to determine where the leaves are. 

• On tropical forest floors, grasses have broad leaves that are more effective at gathering light than narrow “grassy” leaf blades would be. Abundant water resources allow tropical grasses to maintain relatively large leaves with lots of surface area. 

• Large vertical leaves help plants gather light and avoid falling debris in the forest. Epiphytes with vertical leaves can exploit a unique niche, gathering light that is unavailable to most other plants.

Some tropical plants have unusual leaves and branches. 

• Guarea kunthiana, a tree in the mahogany family, has leaves with irregular edges that form when small pieces of the leaf margins fall away. This mimics damage commonly left by feeding insects, which may deter herbivores from eating them. Very few examples of this unique adaptation are known.

• Guarea kunthiana also grows leaves that look like branches. Its pairs of leaflets, or parts of compound leaves, have a small bud at the end. These buds can continue to grow new leaflets indefinitely, eventually forming a long, woody leaf that looks and functions like a branch. Scientists are unsure what purpose this adaptation serves, but some think it may be an energy conservation strategy, since making new leaves may require less energy than making actual branches. 

• Instead of growing big, showy flowers to attract pollinators, plants in the Columnea genus have green leaves with eye-catching bright-red spots bordering small, nondescript flowers. This may save the plant energy, since growing large flowers requires more resources than growing colorful leaves and small flowers.

• Spines or thorns are not unusual in rainforests. They can cover stems, defending the plant from hungry animals. Spines or thorns can also support long, vining stems by gripping larger plants.

• Buttress roots grow partially above the ground and help anchor plants to stay upright in wet, shifting soil, especially during storms. 

• Like buttress roots, stilt roots grow partially above the ground and help anchor plants, so they stay upright in wet, shifting soil. Sometimes, they can be numerous and strong enough to replace a tree’s stem and trunk. 

• Scientists are still trying to understand the relationships between plants in these habitats. While competition for resources like light is common in plants that live in wet environments, there is evidence that some tropical plants cooperate with each other. Plants with leaves that live for years accumulate epiphylls (from mosses and lichens to algae) that seem to do little harm and may provide benefits such as foliar nutrition. The limbs of large trees in rainforests or cloud forests can host entire microhabitats high above the forest floor by providing structures that support mosses, bromeliads, ferns, lichens, and other epiphytic plants that in turn support a range of animals. 

Cloud Forests

Mountaintops in the tropics are often home to cloud forests, named for the persistent seasonal fog that clings to the canopy. Plants in this environment are often slow-growing due to cool temperatures and low light levels. These conditions protect plants from direct sunlight and other stress factors found in surrounding areas. Cloud forests are threatened by climate change, jeopardizing species adapted to these conditions.

Plants in cloud forests, such as orchids, ferns, and bromeliads, as well as unusual and beautiful tropical pitcher plants, have adaptations that help them thrive in damp, cool conditions. 

• Epiphytes live in the tree canopy on perches that may be pads of organic matter shared with animals or other plants, pockets of canopy soil made of decomposing plants, or holdfasts of exposed roots attached to a tree’s bark. Their specialized roots anchor the plant and absorb nutrients. They do not parasitize or harm the host tree. They can also grow on rocks, and even power lines, absorbing moisture from the air and nutrients from a mix of organic debris that accumulates on branches, creating a kind of nutrient-rich “soup.” 

• Canopy soils act like sponges, absorbing this arboreal “soup” as it washes down trees, which can help plants in dry times. Although this nutrient-laden film of water seems like a meager resource, many hours of rain during the growing season can provide a generous food supply.
• A heavy load of epiphytes can bend or break a weak branch. Tree branches can grow faster on one side to support the extra weight of epiphytes.
• Plants called “root climbers” use specialized aerial roots to attach themselves to trees or rocks. Ivy is a familiar garden example. 

• As in rainforests, pendent leafy branches and leaves are an adaptation to life in the trees, where plants compete for light. Sitting in a tall perch with leaves hanging down the side of trees gives plants access to vertical space they wouldn’t have on the ground and to pollinators that fly and climb around the canopy.

Aquatic Plants and Wetlands

Like tropical rainforests, tropical freshwater ecosystems support many different plants. Most aquatic plants live floating on the surface of water or submerged in shallow areas on the margins of rivers, streams, and ponds, where light penetrates the water. Wetland habitats include mangrove forests, marshes, swamps, lagoons, and bogs. These aquatic environments are found worldwide and vary from region to region and season to season. These include freshwater, saltwater, or a mixture of both, and wet, muddy soil. Some aquatic plants are adapted to quiet waters, while others grow in streams or rivers, or at the edges of these bodies of water.

Historically undervalued, wetlands support many endangered species, purify water, and help control erosion. 

The Rose Hills Foundation Conservatory for Botanical Science’s bog habitat displays some of The Huntington’s most unusual American plants, including several carnivorous plants and sphagnum moss from the Carolinas, Georgia, and Florida coastal bogs.

Despite having nutrient-poor soils, these low-lying beds of soggy moss are where carnivorous plants like Venus flytraps, American pitcher plants, sundews, butterworts, and bladderworts thrive using amazing adaptations to catch their prey.

Plants in aquatic environments often have soft, delicate leaves and stems because they do not need to cope with wind, frost, and arid conditions. They can be floating, submerged, or emergent.

• Emergent aquatic plants have parts that stick out above the water, with roots in mud below the surface. This adaptation helps plants capture as much sunlight as possible.

• Floating aquatic plants have feathery roots that do not anchor them in the soil. Instead, they rise and fall with the water level, and their fine roots absorb nutrients directly from the water. Flat leaves floating on the water’s surface use their surface area to catch sunlight.

• Submerged aquatic plants live entirely underwater and can thrive in calm or fast-flowing water. They often have spongy tissues with small compartments of air that help support them in water. Their thin leaves, while flimsy in appearance, help them move with the water. 

Additional Resources

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