I suppose one could say if you want to help the planet, plant a plant. The importance of plants, especially green plants, cannot be overstated. They are a food source, they produce oxygen, they help control natural events, and they stabilize the soil. This is the short list, but you should get the idea.
Ultimately, everything eats plants or plant remains. Plants are the primary producers on our planet. Even deep sea plants that use chemosynthesis instead of photosynthesis are producers. All herbivores and omnivores eat plants and their seeds.
The variety of ways that creatures eat plants is astounding. Some only eat grasses. Others only nibble leaves. A few eat the bark or stems. Creatures that eat plants range from microbes to elephants to some types of whales. As animals become larger, they consume more and more plants. When populations become too dense, plant life is reduced often to non-existent. If those animals cannot find new foraging territory, they become non-existent, too.
All tertiary consumers and scavengers depend plants to sustain their food source. Even the tiny organisms that break down the rotting remains of other organisms need plants to produce food first.
By producing oxygen as a byproduct of food production, plants inadvertently give other organisms the main tool needed to burn food calories. Without oxygen, no food energy could be released to nourish other life. Even the cells in the plants themselves have to draw on this oxygen supply for growth and reproduction.
Large forests become important to the food chain by helping to control some natural disasters and protect the animals that consume them. High winds, even tornadoes, are affected by large, dense forests. It is speculated that rain forests need a certain critical mass to maintain the humid and rainy conditions. The forests create the climate not the other way around.
Plants of all sizes with root systems stabilize the soil. Without them, severe erosion can occur destroy the ability of the land to support major plant growth. In the absence of soil and plants, animals cannot stay either. This is why conservationist push to leave native forests and grasslands alone. By preserving the soil, all life benefits.