Rhodymenia palmata vs red algae

Rhodymenia palmata and red algae both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rhodymenia palmata	Yes	No	No	No
red algae	Yes	No	No	No

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

Rhodymenia palmata: coarse edible red seaweed
red algae: marine algae in which the chlorophyll is masked by a red or purplish pigment; source of agar and carrageenan

Rhodymenia palmata (noun)	red algae (noun)
coarse edible red seaweed	marine algae in which the chlorophyll is masked by a red or purplish pigment; source of agar and carrageenan