seed fern vs gymnosperm

seed fern and gymnosperm both are nouns.

Word	Noun	Adjective	Verb	Adverb
seed fern	Yes	No	No	No
gymnosperm	Yes	No	No	No

As nouns, gymnosperm is a hypernym of seed fern; that is, gymnosperm is a word with a broader meaning than seed fern:

seed fern: an extinct seed-producing fernlike plant of the order Cycadofilicales (or group Pteridospermae)
gymnosperm: plants of the class Gymnospermae having seeds not enclosed in an ovary

seed fern (noun)	gymnosperm (noun)
an extinct seed-producing fernlike plant of the order Cycadofilicales (or group Pteridospermae)	plants of the class Gymnospermae having seeds not enclosed in an ovary