According to the Office of Response and Restoration, oil spills generally affect plants through the chemical components of oil. Different types of oil behave differently and affect living organisms in varying ways.
Fuel oils, such as diesel fuel and gasoline, are classified as light oils, which evaporate relatively quickly and typically do not remain for a long time in the environment, the Office of Response and Restoration explains. They tend to evaporate fast when spread out on the water. However, light oils are hazardous in two ways: they can ignite or explode, and they are considered poisonous. They are dangerous to plants and animals and are also harmful to people who breathe their fumes.
Heavy oils, such as bunker oils, are black and sticky and usually persist in the environment for months or even years. They are typically less dangerous compared to lighter oils, but they present short-term threats, such as smothering organisms, and long-term threats, such as chronic health effects.
The Encyclopedia of Earth explains that rooted or floating plants and grasses are harmed when oil is spilled in the open water. Oil slicks that spread across the surface of the water tend to harm floating plants, such as water lilies. Oil spills also coat important animal habitat and food sources, such as grasses and weeds.