algae

A group of aquatic plants having no roots, stems, or leaves.
(singular alga) Diverse group of plants (including those commonly called seaweeds) that shows great variety of form, ranging from single-celled forms to multicellular seaweeds of considerable size and complexity.
Marine algae help combat global warming by removing carbon dioxide from the atmosphere during photosynthesis.
Because of their diversity, botanists have established seven separate algae groupings or divisions, belonging to three different kingdoms: Cyanobacteria (blue-green algae) of the kingdom Monerans; Chrysophyta (golden algae diatoms), Englenophyta (plidosynthetic flagellates) and Pyrrophyta (dinoflagellates) of the kingdom Protists; and Rhodophyta (red algae), Phaeophyta (brown algae), and Chlorophyta (green algae) of the kingdom Plants.
Microscopic plants which contain chlorophyll and live floating or suspended in water. They also may be attached to structures, rocks or other submerged surfaces. They are food for fish and small aquatic animals. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH and dissolved oxygen of the water