alga vs algae

alga and algae both are nouns.

Word	Noun	Adjective	Verb	Adverb
alga	Yes	No	No	No
algae	Yes	No	No	No

As nouns, alga and algae are synonyms defined as:

alga and algae: primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves

alga (noun)	algae (noun)
primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves	primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves