Definitions

from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun Any of numerous photosynthetic organisms of aquatic or moist habitats, ranging in size from single-celled diatoms to large seaweeds such as kelp, and characterized by a lack of complex organs and tissues. Once classified within the plant kingdom, the algae are now considered to include several unrelated groups belonging to different kingdoms.

from The Century Dictionary.

  • noun A cryptogam of the class of Algæ.

from the GNU version of the Collaborative International Dictionary of English.

  • noun (Bot.) A kind of seaweed; pl. the class of cellular cryptogamic plants which includes the black, red, and green seaweeds, as kelp, dulse, sea lettuce, also marine and fresh water confervæ, etc. The algae are primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun biology Any of many aquatic photosynthetic organisms, whose size ranges from a single cell to giant kelps and whose form is very diverse; some are eukaryotic and some prokaryotic; includes the seaweeds.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves

Etymologies

from The American Heritage® Dictionary of the English Language, 4th Edition

[Latin, seaweed.]

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Examples

  • The alga, which is native to the Pacific Ocean, first showed up three years ago in

    Sun Journal top news 2010

  • In one, domestic sewage is utilized to produce an alga which is then used for fish culture.

    Chapter 13 1979

  • It is simply the blue-green alga trichodesmus that imparts a red color to water!

    Rabbi Samuel April: Today's 10 Plagues Rabbi Samuel April 2011

  • It is simply the blue-green alga trichodesmus that imparts a red color to water!

    Rabbi Samuel April: Today's 10 Plagues Rabbi Samuel April 2011

  • Without these mutations springing up to propel a single-celled organism into full humanity, we'd still be a smear of blue-green alga on a rock.

    Archive 2009-09-01 2009

  • Potter was originated the idea that lichens were a symbiosis between a fungus and an alga.

    Ada Lovelace Day – Heuristic 2009

  • But we also might consider yeast and other fungi, or even unicellular alga.

    A Tetrahymena Puzzle 2008

  • If you want carbon sequestration in the ocean, dump some powdered iron in, the alga bloom will take up tons of CO2, and it will certainly be cheaper and more effective than this hair-brained bag scheme. zilfondel Says:

    Storing CO2 in Giant Underwater Plastic Bags? | Inhabitat 2008

  • However, algae that secrete calcium carbonate, such as coralline red algae and an abundant calcifying green alga known as Halimeda, are almost always significant contributors as well.

    Coral reef 2010

  • But these are being overrun by Codiaceae algae in the shallows and by pea-soup alga Caulerpa taxifolia in deeper water.

    Everglades National Park, United States 2009

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