There are over 250,000 species that make up the kingdom plantae, which is the second largest kingdom after the animal kingdom. When you think of a plant, that green stuff that grows inside your fish tank probably isn't the first thing that comes to mind, but algae is in the kingdom plantae. In fact, there are over 12,000 different species of algae: some brown, some green and some red. And you thought all plants were green! Typically, plants are green due to chlorophyll , or green pigment that helps the plant get energy from the sun. In the case of some of the algae, the chlorophyll combines with other pigments to make the red or brown. Algae are an important piece of the food chain in marine and freshwater environments.