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nounused in some classification systems: a group of extinct fossil gymnosperms coextensive with the order Cycadofilicalestype of:
Definition that contains pteridospermae
- seed fern an extinct seed-producing fernlike plant of the order Cycadofilicales (or group Pteridospermae)
- pteridosperm an extinct seed-producing fernlike plant of the order Cycadofilicales (or group Pteridospermae)