nostoc vs blue-green algae

nostoc and blue-green algae both are nouns.

Word	Noun	Adjective	Verb	Adverb
nostoc	Yes	No	No	No
blue-green algae	Yes	No	No	No

As nouns, blue-green algae is a hypernym of nostoc; that is, blue-green algae is a word with a broader meaning than nostoc:

nostoc: found in moist places as rounded jellylike colonies
blue-green algae: predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton

Other hypernyms of nostoc include cyanobacteria.

nostoc (noun)	blue-green algae (noun)
found in moist places as rounded jellylike colonies	predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton