alga

noun

al·​ga ˈal-gə 

plural algae ˈal-(ˌ)jē  also algas

: 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

Note: 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

algal

ˈal-gəl 

adjective

algal cells

Stimulated by warm, still weather, algal blooms deoxygenate the water below.

—William Booth

Examples of alga in a Sentence

Recent Examples on the Web

The carotenoid pigments in this alga gives flamingos their pinkish hue. —Joshua Rapp Learn, Smithsonian Magazine, 23 July 2024

Instead, the alga survived and became a symbiotic partner to the protozoan, feeding it the fruits of its photosynthesis. —Kevin Hartnett, Quanta Magazine, 6 July 2023

The adults, after all, have opaque bodies and spend most of their lives underground – conditions that are less than ideal for a light-dependent alga. —Ed Yong, Discover Magazine, 5 Apr. 2011

Soon, all parts of each alga will be used. —Hannah Hall, Washington Post, 9 Jan. 2023

Word History

Etymology

Latin, seaweed

First Known Use

circa 1527, in the meaning defined above

Phrases Containing alga

• blue-green alga
• brown alga
• golden alga
• golden-brown alga
• green alga
• red alga
• yellow-green alga

Kids Definition

alga

noun

al·​ga ˈal-gə 

plural algae ˈal-(ˌ)jē 

: any plant or plantlike organism (as a seaweed) that includes forms mostly growing in water, lacking a system of vessels for carrying fluids, and often having chlorophyll masked by brown or red coloring matter

algal

ˈal-gəl 

adjective

Medical Definition

alga

noun

al·​ga ˈal-gə 

plural algae ˈal-(ˌ)jē  also algas

: 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

algal

-gəl 

adjective