brown algae vs algae

brown algae and algae both are nouns.

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

As nouns, algae is a hypernym of brown algae; that is, algae is a word with a broader meaning than brown algae:

brown algae: algae having the chlorophyll masked by brown and yellow pigments
algae: primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves

Other hypernyms of brown algae include alga.

brown algae (noun)	algae (noun)
algae having the chlorophyll masked by brown and yellow pigments	primitive chlorophyll-containing mainly aquatic eukaryotic organisms lacking true stems and roots and leaves