:''This article defines the Gleicheniales in a loose sense. For the restricted definition, see
Gleicheniaceae
The forked ferns are the family Gleicheniaceae, which includes six genera and about 160 known species. The formerly independent families Dicranopteridaceae and Stromatopteridaceae are generally included in the Gleicheniaceae, whereas the Dipterid ...
.''
Gleicheniales is an
order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
of
fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
s in the subclass Polypodiidae (the
leptosporangiate fern
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 ...
s). The Gleicheniales have records potentially as early as the
Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
, but the oldest unambiguous records date to the
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...
.
Description
These ferns are characterized by root
stele
A stele ( ),Anglicized plural steles ( ); Greek plural stelai ( ), from Greek , ''stēlē''. The Greek plural is written , ''stēlai'', but this is only rarely encountered in English. or occasionally stela (plural ''stelas'' or ''stelæ''), whe ...
s having 3–5
protoxylem
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
poles and
antheridia
An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also t ...
with 6–12 narrow, twisted or curved cells in their walls.
Otherwise, their
habitus is highly diverse, including plants with the typical fern
frond
A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
s, others whose leaves resemble those of
palm tree
The Arecaceae is a family of perennial flowering plants in the monocot order Arecales. Their growth form can be climbers, shrubs, tree-like and stemless plants, all commonly known as palms. Those having a tree-like form are called palm trees ...
s, and yet others again which have undivided leaves. They are
tropical
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
ferns, most diverse in
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
and the
Pacific
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
region.
Classification
In the molecular phylogenetic classification of Smith et al. in 2006, the Gleicheniales were placed in class
Polypodiopsida
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except th ...
(the
leptosporangiate fern
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 ...
s). Three families,
Dipteridaceae
The Dipteridaceae is a family (biology), family of ferns in the order Gleicheniales of the class Polypodiopsida. They are commonly known as umbrella ferns and contain two genera, ''Cheiropleuria'' and ''Dipteris'', with a total of nine species c ...
,
Gleicheniaceae
The forked ferns are the family Gleicheniaceae, which includes six genera and about 160 known species. The formerly independent families Dicranopteridaceae and Stromatopteridaceae are generally included in the Gleicheniaceae, whereas the Dipterid ...
, and
Matoniaceae
Matoniaceae is one of the three families of ferns in the Gleicheniales order of the Polypodiopsida class. Fossil records reveal that Matoniaceae ferns were abundant during the Mesozoic era (about 250-million to 66-million years ago), during which ...
were recognized.
The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009)
which placed all land plants in Equisetopsida, reclassified Smith's Polypodiopsida as subclass
Polypodiidae Polypodiidae may refer to:
* Polypodiidae (cnidarians), a zoological family that only includes ''Polypodium hydriforme'', a cnidarian parasite of fish eggs
*Polypodiidae (plant), a botanical subclass of Equisetopsida sensu lato that includes the le ...
and placed the Gleicheniales there. The circumscription of the order and its families was not changed,
and that circumscription and placement in Polypodiidae has subsequently been followed in the classifications of Christenhusz and Chase (2014)
and PPG I (2016).
The
form taxon
Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of sc ...
''
Microphyllopteris'' is used for some
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
Gleicheniales that cannot be reliably assigned to the present-day orders. The
Triassic
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
''
Antarctipteris'' and ''
Gleichenipteris'' are sometimes ascribed to the Gleicheniaceae, but are probably better considered Gleicheniales ''
incertae sedis
' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
''.
The oldest possible members of the family are members of the genus ''
Oligocarpia'' (reproductive organs) from the Carboniferous. However, these have alternatively been considered members of
Sermayaceae. The oldest unambiguous records, belonging to the family Gleicheniaceae, are known from the Wuda Tuff flora of China, dating to the Asselian, approximately 298.34 million years ago.
In historical treatments, the order has sometimes been treated as a
subclass Gleicheniatae of the Pteridopsida, with the
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
treated as
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...
here upranked to orders, so that a distinct subclass can be established for the
leptosporangiate fern
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 ...
s. In other treatments, they were expanded to include the
filmy fern
The Hymenophyllaceae, the filmy ferns and bristle ferns, are a family of two to nine genera (depending on classification system) and about 650 known species of ferns, with a cosmopolitan distribution, subcosmopolitan distribution, but generally r ...
s (order Hymenophyllales), as well as the similar-looking
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''
Hymenophyllopsis'' (as order
Hymenophyllopsidales). The resultant group was treated as
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
Gleichenopsida alongside the
Pteridopsida
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 ...
, which would then be limited to the leptosporangiate ferns. However, this class is not
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 ...
but rather a
basal grade
Grade most commonly refers to:
* Grade (education), a measurement of a student's performance
* Grade, the number of the year a student has reached in a given educational stage
* Grade (slope), the steepness of a slope
Grade or grading may also ref ...
, retaining ancient traits among the living ferns.
Irrespective of their modern taxonomic treatment, the Gleicheniales were formerly included in the order
Polypodiales
The order Polypodiales encompasses the major lineages of polypod ferns, which comprise more than 80% of today's fern species. They are found in many parts of the world including tropical, semitropical and temperate areas.
Description
Polypodiale ...
. But the ferns in the loose sense are much too diverse a group to be shoehorned into one
taxon
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
at such a low rank.
The following diagram shows the phylogeny of Gleicheniales.
Footnotes
References
* (2006): A classification for extant ferns. ''Taxon'' 55(3): 705–731
PDF fulltext
{{Taxonbar, from=Q1209668
Fern orders