Eusporangiate ferns are vascular spore plants, whose

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...

arise from several epidermal cells and not from a single cell as in

leptosporangiate ferns The Polypodiidae, commonly called leptosporangiate ferns, formerly Leptosporangiatae, are one of four subclasses of ferns, and the largest of these, being the largest group of living ferns, including some 11,000 species worldwide. The group has ...

. Typically these ferns have reduced root systems and sporangia that produce large amounts of

spores In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

(up to 7000 spores per sporangium in '' Christensenia'') There are four extant eusporangiate fern families, distributed among three classes. Each family is assigned to its own order. *Class Psilotopsida **Order Psilotales, family

Psilotaceae Psilotaceae is a family of ferns (class Polypodiopsida) consisting of two genera, ''Psilotum'' and '' Tmesipteris'' with about a dozen species. It is the only family in the order Psilotales. Description Once thought to be descendants of early v ...

– Whisk ferns (2 genera, about 17 species) **Order Ophioglossales, family

Ophioglossaceae Ophioglossaceae, the adder's-tongue family, is a small family of ferns. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is the only family in the order Ophioglossales, which together with the Psilotales is placed in the s ...

– Adder's-tongues (5 genera, about 80 species) *Class Equisetopsida **Order

Equisetales Equisetales is an order of subclass Equisetidae with only one living family, Equisetaceae, containing the genus '' Equisetum'' (horsetails). Classification In the molecular phylogenetic classification of Smith et al. in 2006, Equisetales, in i ...

, family Equisetaceae – Horsetails (1 genus, about 15 species) *Class

Marattiopsida Marattiaceae is the only family of extant (living) ferns in the order Marattiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), Marattiales is the only order in the subclass Marattiidae. The family has six genera and abou ...

**Order

Marattiales Marattiaceae is the only family of extant (living) ferns in the order Marattiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), Marattiales is the only order in the subclass Marattiidae. The family has six genera and abou ...

, family Marattiaceae – Marattoid ferns (6 genera, about 500 species) The following diagram shows a likely phylogenic placement of eusporangiate fern classes within the

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

Cladistics

While it is generally accepted that the leptosporangiate ferns are

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

, it is considered to be likely that the eusporangiate ferns, as a group, are

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

. In each of the three examples from recently published studies, shown in the following table, it can be seen that, together, the four eusporangiate fern families do not form a single clade.

References

* Hogan, C.Michael. 2010
''Fern''. Encyclopedia of Earth, National Council for Science and the Environment
topic ed. Saikat Basu *Sporne, K. R. 1962. The morphology of pteridophytes, the structure of ferns and allied plants. pp. 127–135. Hutchison & Co. London. {{Taxonbar, from=Q2624762 Ferns