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Schizaeales is an order of ferns (class Polypodiopsida).


Description

While the three clades of Schizaeales are all well-distinguished from one another by numerous morphological characters, members of the order all have dimorphic fertile and sterile fronds and lack well-defined sori. Their
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 ...
have a horizontal annulus that lies below and completely encircles the top of the sporangium.


Classification

In the molecular phylogenetic classification of Smith et al. in 2006, the Schizaeales were placed in the
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 ...
, 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 ...
. Three families,
Anemiaceae ''Anemia'' is a genus of ferns. It is the only genus in the family Anemiaceae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the genus may be placed as the only genus in the subfamily Anemioideae of a more broad ...
,
Lygodiaceae ''Lygodium'' (climbing fern) is a genus of about 40 species of ferns, native to tropical regions across the world, with a few temperate species in eastern Asia and eastern North America. It is the sole genus in the family Lygodiaceae in the Pter ...
, and
Schizaeaceae Schizaeaceae is a family of ferns in the order Schizaeales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it includes only two genera. Alternatively, two families kept separate in PPG I, Lygodiaceae and Anemiaceae, may be ...
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 and placed the Schizaeales there, with the same three families. The classification of Christenhusz and Chase (2014) placed all members of the Schizaeales in a more broadly defined Schizaeaceae, reducing the three existing families to subfamilies as Anemioideae, Lygodioideae, and Schizaeoideae. The PPG I classification (2016) returned to the three-family definition of the order. Historically, the ferns in this order were once all lumped into the family Schizaeaceae in the old order Filicales. However, although they are demonstrably related, these ferns differ markedly, and so three groups have now been elevated to family status: * The family
Schizaeaceae Schizaeaceae is a family of ferns in the order Schizaeales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it includes only two genera. Alternatively, two families kept separate in PPG I, Lygodiaceae and Anemiaceae, may be ...
are generally small ferns with forking
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 and a distinctive, somewhat non-fern-like, appearance. * The family
Anemiaceae ''Anemia'' is a genus of ferns. It is the only genus in the family Anemiaceae in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). Alternatively, the genus may be placed as the only genus in the subfamily Anemioideae of a more broad ...
look very fern-like and are typically terrestrial or epipetric. * The family
Lygodiaceae ''Lygodium'' (climbing fern) is a genus of about 40 species of ferns, native to tropical regions across the world, with a few temperate species in eastern Asia and eastern North America. It is the sole genus in the family Lygodiaceae in the Pter ...
, or climbing ferns, look very ferny but are highly distinctive in their growth habit: the rachis of the frond is long and flexible, with indeterminate growth, so that the fronds form climbing or trailing vines. At one time some workers believed the water ferns (order
Salviniales The order Salviniales (formerly known as the Hydropteridales and including the former Marsileales) is an order of ferns in the class Polypodiopsida. Description Salviniales are all aquatic and differ from all other ferns in being heterosporous ...
) to be allied to this order because of certain structural similarities, but modern cladistic studies have ruled out any special alliance.


Evolution

Schizaeales had a northern hemisphere concentration as late as the Mesozoic, but by the Quaternary, there was a clear shift to a southern hemisphere distribution.


References

* C.Michael Hogan. 2010
''Fern''. Encyclopedia of Earth, National Council for Science and the Environment
topic ed. Saikat Basu {{Taxonbar, from=Q139031 Fern orders