Schizaeales is an order 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 exce ...
s (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 cyc ...
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 exce ...
. Three families,
Anemiaceae,
Lygodiaceae, and
Schizaeaceae 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 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 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 look very fern-like and are typically terrestrial or epipetric.
* The family
Lygodiaceae, 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
vine
A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' "wine") is any plant with a growth habit of trailing or scandent (that is, climbing) stems, lianas or runners. The word ''vine'' can also refer to such stems or runners themsel ...
s.
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