Plants play a role in nearly every ecosystem on Earth. Living in the variety of environments on Earth requires each plant species to have unique adaptations (beneficial features) to survive and reproduce in their surroundings. This is why you would not see a cactus growing in the rainforest, nor a water lily thriving in a desert. Physical or chemical adaptations also help a plant go on the defensive against predators, or allow better distribution of pollen or seeds!
- A xerophyte is a plant that is adapted to dry environments, such as a desert. They can store water (thick stems) and have other means to get water (large root systems) or prevent too much transpiration (reduced leaves). A cactus, for instance has very deep, widespread roots and no leaves. It also has tissue that stores water and is covered in sharp spines (modified leaves) to protect it from animals that might eat its juicy flesh.
- A hydrophyte is a plant that is adapted to live in very watery environments. These plants may not need highly developed root systems to capture water, but they usually have leaf adaptations to float (water lily) or resist moving water. They also have large air spaces in their tissues to float and to allow for diffusion of oxygen into their tissues. Roots of mangroves or cypress trees protrude above the water to get oxygen and shunt it to parts underwater.
- Epiphytes do not live off of the soil or ground and instead grow on the branches of trees. Many epiphytes live in the rainforest or other humid environments where they can get moisture from the air, and therefore do not require extensive root systems. Some collect water in their cone shaped flowers or leaves, providing homes to insects or frogs.
Stop and think: Examine the plants below.Can you identify the epiphyte, xerophyte and hydrophyte? (Answer: hydrophyte, epiphyte, xerophyte)
Defensive adaptations help a plant protect them from being eaten. They can be physical or chemical.
- Physical defenses include thorns (modified stems) and spines (modified leaves) as well as hard shells around seeds.
- Chemical defenses include poisons, bitter tasting chemicals, or chemicals that disrupt insect development and reproduction.
The coconut protects its seeds with a thick, physical armor. The foxglove plant is filled with a number of chemicals that can cause nausea/vomiting, hallucinations and death.
Some of the most interesting plants are carnivorous plants. These plants have special, adaptive structures that are modified to catch prey. Once trapped, their prey are digested with enzymes and absorbed to supply the plant with nutrients. They still photosynthesize for energy, but because they tend to grow in nutrient poor soil, the adaptation to capture/digest other organisms helps them supplement what the soil lacks. Watch the time-lapse video below of a sundew plant devouring a trapped insect.
Some plants are parasites, their roots growing directly into another host plant and tapping into their nutrients.
Mistletoe is a parasitic plant, growing on the trunks or branches of other trees and sometimes killing them, but it is also considered a keystone species for its ecosystem because it is an important food source.
Reproductive adaptations will be discussed in detail later in this module, but we can mention here that providing a pollinator with a reason to visit a flower (showy colors, looks like a mate) is a great adaptation that disperses pollen to other flowers. By the same token a seed with a papery wing or a juicy fruit helps that new plant (the seed) travel much farther from the parent (that it would normally compete with for light, nutrients).
Stop and Think: Watch the following video about the Wild Tobacco Plant (How Plants Defend Themselves, A Merit Motion Pictures Production © 2013 Thirteen). How many different adaptations can you identify in this plant?
Watch the Plant Structure and Adaptation video below from the Amoeba Sisters by clicking on the image. The video will open in a new window and be patient as it loads. Use it to review concepts from this lesson and prepare for the upcoming quiz.