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The earliest cycad fossils are from the Permian period (about 300 million years ago). Paleobotanists believe that cycads evolved from the seed ferns, a large group of primitive, seed-bearing plants with fern-like leaves. The seed ferns originated at least 350 million years ago, and became extinct more than 200 million years ago.

Although cycads are considered to be gymnosperms, because they bear naked seeds which are not enclosed by a fruit, fossil evidence suggests they are not closely related to other gymnosperms, such as the conifers. Therefore, many paleobotanists consider the gymnosperms to be an unnatural grouping of unrelated plants.

Cycads were particularly abundant and diverse during the Mesozoic era, so paleobotanists often refer to the Mesozoic as "the age of cycads." This is also the era during which dinosaurs were the dominant animals, so zoologists refer to this as "the age of dinosaurs." Consequently, museum drawings and dioramas which depict re-creations of dinosaur life typically show cycads as the dominant plants.

The cycads are no longer a dominant group of plants, and there are only about 200 extant (surviving) species. The flowering plants essentially replaced the cycads as ecologically dominant species on land more than 100 million years ago.

See also Paleobotany.



Jones, D. C. Cycads of the World. Washington, DC: Smithsonian Institute Press, 1993.

Margulis, L., and K.V. Schwartz. Five Kingdoms. New York: W. H. Freeman and Company, 1988.

Peter A. Ensminger


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Cyanobacteria (singular, cyanobacterium)

—Photosynthetic bacteria, commonly known as blue-green algae.


—Nucleus or cell containing two copies of each chromosome, generated by fusion of two haploid nuclei.


—The haploid, gamete-producing generation in a plant's life cycle.


—Nucleus or cell containing one copy of each chromosome.


—A radial cluster of leaves, often on a short stem.


—An evolutionarily modified leaf which produces spores.


—The diploid, spore-producing generation in a plant's life cycle.

Additional topics

Science EncyclopediaScience & Philosophy: Cyanohydrins to Departments of philosophy:Cycads - General Characteristics, Life Cycle, Evolution