Presented below is a photomicrograph of algae filaments, showing cells arranged in chains with spiral chloroplasts visible inside each cell. This digital image was captured with the DXM 1200 ACT-1 control software in single-image acquisition mode utilizing DIC illumination.

Members of the Kingdom Protista, algae are most common in aquatic habitats, but occur in nearly every environment. They range in size from microscopic to giant kelp that reach 200 feet (60 meters) in length. Algae produce a significant percentage of the Earth's oxygen, are the base of the food chain for nearly all aquatic life, and provide food and industrial products for humans.

Algae are classified into several types based on the morphology of their vegetative, or growing, state. Filamentous algae have cells arranged in chains and an overall appearance like strings or filaments. Some filaments are unbranched, while others have extensive branching, giving them a bushlike appearance.