Chlorophyllous plants are plants that contain chlorophyll, which is a green pigment found in most plants and is essential for photosynthesis. An example of a chlorophyllous plant is an ALGA, which is a type of aquatic plant that lives in water and has no roots, stems, or leaves. Algae are important for their ability to produce oxygen and absorb carbon dioxide, making them essential for the health of aquatic ecosystems.