Cycadidae is a subclass of

Equisetopsida Equisetidae is one of the four subclasses of Polypodiopsida (ferns), a group of vascular plants with a fossil record going back to the Devonian. They are commonly known as horsetails. They typically grow in wet areas, with whorls of needle-like ...

in the sense used by Mark W. Chase and

James L. Reveal James Lauritz Reveal (March 29, 1941 – January 9, 2015) was a U.S. botanist best known for his contributions to the genus '' Eriogonum'' and for his work on suprageneric names. His website, at PlantSystematics.org, also presents material on plan ...

in their 2009 article "A phylogenetic classification of the land plants to accompany

APG III APG is an abbreviation with several different meanings: * Aberdeen Proving Ground, a United States Army installation in Aberdeen, Maryland, also ** Phillips Army Airfield, the airfield of the above, from its IATA airport code * Aboriginal Provisiona ...

." This subclass comprises the

cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...

s, which include the two families

Cycadaceae ''Cycas'' is a genus of plants belonging to a very ancient lineage, the Cycadophyta, which are not closely related to palms, ferns, trees or any other modern group of plants. They are evergreen perennials which achieved their maximum diversity in ...

and

Zamiaceae The Zamiaceae are a family of cycads that are superficially palm or fern-like. They are divided into two subfamilies with eight genera and about 150 species in the tropical and subtropical regions of Africa, Australia and North and South America ...

Phylogeny

The following diagram shows a likely phylogenic relationship between subclass Cycadidae and the other Equisetopsida subclasses.

References

Equisetopsida sensu lato Plant subclasses {{cycad-stub