Columbia subject headings:
Gymnosperms--Evolution.
Gymnosperms--Origin.
Paleobotany.
Harvard subject headings:
Gymnosperms, Fossil.
Gymnosperms--Evolution.
Gymnosperms--Origin.
Paleobotany.
Princeton subject headings:
Gymnosperms, Fossil.
Gymnosperms--Evolution.
Gymnosperms--Origin.