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 cyc ...
arise from several
epidermal cells
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
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, f ...
(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
Ophioglossidae is one of the four subclasses of Polypodiopsida (ferns). This subclass consists of the ferns commonly known as whisk ferns, grape ferns, adder's-tongues and moonworts. It is equivalent to the class Psilotopsida in previous treat ...
**Order Psilotales
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 va ...
, 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 va ...
– Whisk ferns (2 genera, about 17 species)
**Order Ophioglossales
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 su ...
, family Ophioglossaceae – Adder's-tongues (5 genera, about 80 species)
*Class 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 ...
**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 its ...
, family Equisetaceae
Equisetaceae, sometimes called the horsetail family, is the only extant family of the order Equisetales, with one surviving genus, ''Equisetum'', which comprises about twenty species.
Evolution and systematics
Equisetaceae is the only survivin ...
– 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 about ...
**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 about ...
, family Marattiaceae
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 about ...
– Marattoid ferns (6 genera, about 500 species)
The following diagram shows a likely phylogenic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
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 al ...
s.[
]
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 gro ...
, it is considered to be likely that the eusporangiate ferns, as a group, are paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
.[ 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