There are thousands of algae species spanning the Monera, Plantae and Protista kingdoms. Green algae species are members of Plantae, the plant kingdom. They share many characteristics unique to plants, but have only recently been included in that kingdom in the established taxonomic structure. Green algae is often confused with Blue-Green algae, which is actually a bacterial species and member of the Monera kingdom.
Both green algae and plants produce energy through the process of photosynthesis. Their cells contain chlorophyll, which allows them to capture sunlight as energy. This molecule gives living algae and plant cells a distinct green color. Some species of bacterial algae can photosynthesize, but they are not classified as green species.
Algae growths are simply a collection of one-celled organisms, even though they closely resemble structured plant life. Algae cells can form basic bonds with one another, forming strands or other basic shapes. Plants comprise an intricate structure of roots, leaves and stems. They are also equipped with the means to transport nutrients among various specialized cells.
Plant cells are protected by a cell wall made of tough fiber. This allows plants to grow vertically or form gravity-defying structures. Algae only has a membrane, similar to animal cells, to protect it from its environment. Plant cells can specialize by adapting to perform a limited function, like root cells. Each algae cell is a unique organism and must be self-sufficient. This limits its ability to form complex, larger structures.
Plants and algae compete directly with each other in aquatic environments, especially small ponds and rivers. Both produce oxygenated water, which is essential for fish life, but can strangle out other organisms if left unchecked. Gardeners often plant a variety of floating or oxygenating plants in decorative pools or ponds to prevent algae growth. Both consume nitrogen-based nutrients from the water and provide food or shelter for animals.