Equisetopsida is the name of a class of plants that traditionally contains the single genus Equisetum (horsestails). However, in 2009, in an article titled "A phylogenetic classification of the land plants to accompany APG III," Mark W. Chase and James L. Reveal proposed a much broader sense for the Equisetopsida class name. In their system, Equisetopsida includes all land plants (embryophytes). Their rationale was that "If the major clades of green algae are recognized as classes, then all land plants, the embryophytes, should be included in a single class..."
The class Equisetopsida sensu Chase & Reveal, 2009, contains the following subclasses. Traditional divisions and classes, along with common names are shown in parentheses.
bryophytes (non-vascular plants)
Subclass Marchantiidae Engl. 1893 (div. Marchantiophyta, 3 classes - liverworts)
Subclass Bryidae Engl. 1892 (div. Bryophyta, class Bryopsida - moss)
Subclass Anthocerotidae Engl. 1893 (div. Anthocerotophyta, 2 classes - hornwort)
lycopodiophytes
Subclass Lycopodiidae Bek. 1863 (div. Lycopodiophyta, 2 classes - clubmoss, spikemoss, quillworts)
monilophytes (ferns)Subclass Equisetidae Warm. 1883 (class Equisetopsida, s.s. - horsetails)
Subclass Ophioglossidae Klinge 1882 (class Psilotopsida - whisk ferns, grape-ferns, moonworts)
Subclass Marattiidae Klinge 1882 (class Marattiopsida - marattioid ferns)
Subclass Polypodiidae Cronquist, Takht. & W. Zimm. 1966 (class Polypodiopsida - polypod ferns)
Subclass Psilotidae Reveal 1996 [merged into Ophioglossidae by Christenhusz, 2011]
gymnospermsSubclass Cycadidae Pax 1894 (div. Cycadophyta, class Cycadopsida - cycads)
Subclass Ginkgoidae Engl. 1897 (div. Ginkgophyta, class Ginkgoopsida, one extant genus: Ginko)
Subclass Gnetidae Pax 1894 (div. Gnetophyta, class Gnetopsida - gnetophytes)
Subclass Pinidae Cronquist, Takht. & W. Zimm. 1966 (div. Pinophyta, class Pinopsida - conifers)
angiospermsSubclass Magnoliidae Novák ex Takht. 1967 (Angiosperms - flowering plants)
The following diagram shows a likely phylogenic relationship between the Equisetopsida subclasses.
