algae

American  

[al-jee] / ˈæl dʒi /

plural noun

1. Microbiology. any of numerous groups of chlorophyll-containing, mainly aquatic, eukaryotic organisms ranging from microscopic single-celled forms to multicellular forms 100 feet (30 meters) or more long, distinguished from plants by the absence of true roots, stems, and leaves and by a lack of nonreproductive cells in the reproductive structures: classified into the six phyla Euglenophyta, Crysophyta, Pyrrophyta, Chlorophyta, Phaeophyta, and Rhodophyta.

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algae British  

/ ˈældʒiː, ˈælɡəl /

plural noun

1. unicellular or multicellular organisms formerly classified as plants, occurring in fresh or salt water or moist ground, that have chlorophyll and other pigments but lack true stems, roots, and leaves. Algae, which are now regarded as protoctists, include the seaweeds, diatoms, and spirogyra

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algae Cultural  

1. Primitive organisms that contain chlorophyll but do not have structures, such as xylem and phloem, to transport fluids. Algae sometimes contain only a single cell, and nowadays they are not considered members of the plant kingdom.

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Discover More

Algae supply a considerable part of the world's oxygen.

The most familiar algae are the greenish scum that collects in still water.

Other Word Forms

Derived Forms

• algal
  adjective

Etymology

Origin of algae

First recorded in 1790–1800; from New Latin, plural of Latin alga “seaweed”

Compare meaning

How does algae compare to similar and commonly confused words? Explore the most common comparisons:

• algae vs. seaweed

Explanation

Ever walk in the ocean and feel your feet slipping and sliding along the rocks? That slimy green stuff under your feet is algae, a nonflowering plant that grows in the water and has no stems, roots, or leaves. Algae is actually the plural form of the word alga, which in Latin means, you guessed it: "seaweed." Algae isn't just something gross looking floating on the water. It's actually important in aquatic ecology because the tiny organisms that live suspended in algae are the food base for most marine food chains.

Example Sentences

The pool where visitors could swim with otters and penguins was frequently bright green with algae.

From The Wall Street Journal • Jun. 2, 2026

Luke Dawson, a National Trust ranger who helps look after the site, says heavier winter rains are washing chalk from the slope more quickly, while mild, damp conditions give algae more chance to grow.

From BBC • May 27, 2026

Coral's survival depends on a special relationship with a kind of algae.

From Barron's • May 22, 2026

These nutrients make "harmful" blue-green algae more likely which can be dangerous to people and animals.

From BBC • May 20, 2026

A killer whale surfaced beside the ship, its black sides glistening and its white patches tinged a dirty yellow by algae.

From "Shipwreck at the Bottom of the World" by Jennifer Armstrong

Related Words

• seaweed