: any of a diverse group of chiefly photosynthetic and aquatic plantlike organisms that range from unicellular to large multicellular forms, are typically classified as protists, and include the green, yellow-green, brown, golden-brown, and red algae in the eukaryotes and especially formerly the cyanobacteria in the prokaryotes
While multicellular algae often resemble plants, they lack the true roots, leaves, and stems characteristic of vascular plants.
… the divers were witnessing the collapse of the delicate symbiotic relationship between the coral animals and the single-celled photosynthetic algae, called zooxanthellae, that normally flourish within them.—Lucy Bunkley-Williams and Ernest H. Williams, Jr. In the intertidal zone limpets and other mollusks graze on algae in the rocks.—Roger Rosenblatt Diatoms, the preeminent form of algae in most of today's freshwater and marine environments, need high concentrations of nutrients near the water's surface in order to bloom and form mats.—Mrill Ingram But the rapid decline of one of the pond's rare plants, a one-metre long giant freshwater alga called stonewort, has alerted scientists to the fact that changes are taking place at Hell Kettles.—The Journal (Newcastle, England) Giant kelp, the world's largest species of marine algae, is an attractive source for making biofuels.—Diane Kim
Stimulated by warm, still weather, algal blooms deoxygenate the water below.
Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!