class Phaeophyceae vs brown algae

class Phaeophyceae and brown algae both are nouns.

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

class Phaeophyceae (noun)	brown algae (noun)
brown algae; mostly marine and littoral eukaryotic algae	algae having the chlorophyll masked by brown and yellow pigments