Pteridales
Encyclopedia
The Pteridales are fern
s that have their sori
in linear strips under the edge of the leaf tissue, usually with the edge of the lamina reflexed over.
This order is considered a family under the Smith classification. However, this group, a natural clade
, is clearly the most basal offshoot of the entire polypodioid line, and if any portion of that clade is segregated as a separate order, this would be the obvious one. For this reason, and because this is a large and complex group, it is being considered an order for this page.
Most members of this order are small, but some members of the tropical genus
Acrostichum
, in the Ceratopteridaceae
, are immense, with frond
s 3.5 meters (twelve feet) tall.
One of the most well known plants in this order is the maidenhair fern Adiantum, with many forms in cultivation. Also commonly cultivated are various species of Pteris, sometimes known as "table ferns," and some species of Pellaea
, including the button fern.
While this group has long been recognized as distinct from the rest of the polypodioid ferns, relationships within the group have long been misunderstood. A ground-breaking paper by Schuettpelz et al. has redefined this order using not only morphological data, but also extensive genetic data. The cladogram at left is based on their data. Line length in this diagram is not meaningful.
Cheilanthes, Pellaea
, Doryopteris, Jamesonia
, Anogramma
, and Pteris have all been shown to be seriously paraphyletic genera. Jamesonia
and Eriosorus were found to be a highly paraphyletic mixture, although in their own clade. More surprisingly, they found that the vittarioid ferns nest within the genus Adiantum. And they have established that Acrostichum
and Ceratopteris
are allied within their own isolated clade.
Deriving from the results of this important study, it is clear that the Pteridales should include five distinct families, although their final names are yet to be determined:
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s that have their sori
Sorus
A sorus is a cluster of sporangia .In fungi and lichens, the sorus is surrounded by an external layer. In some red algae it may take the form of a depression into the thallus....
in linear strips under the edge of the leaf tissue, usually with the edge of the lamina reflexed over.
This order is considered a family under the Smith classification. However, this group, a natural clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, is clearly the most basal offshoot of the entire polypodioid line, and if any portion of that clade is segregated as a separate order, this would be the obvious one. For this reason, and because this is a large and complex group, it is being considered an order for this page.
Most members of this order are small, but some members of the tropical genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Acrostichum
Acrostichum
Acrostichum was one of the original pteridophyte genera delineated by Linnaeus. It was originally drawn very broadly, including all ferns that had sori apparently "acrostichoid", or distributed in a solid mass across the back of the frond, rather than organized in discrete sori...
, in the Ceratopteridaceae
Ceratopteridaceae
Ceratopteridaceae is the family name for the clade that is now known to include the two genera Ceratopteris and Acrostichum.Although Ceratopteris was long isolated under its own family, due to adaptations for a dedicated aquatic existence, recent genetic study has determined that these two genera...
, are immense, with frond
Frond
The term frond refers to 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...
s 3.5 meters (twelve feet) tall.
One of the most well known plants in this order is the maidenhair fern Adiantum, with many forms in cultivation. Also commonly cultivated are various species of Pteris, sometimes known as "table ferns," and some species of Pellaea
Pellaea
Pellaea is a genus of ferns in the family Pteridaceae. The name is derived from the Greek word πελλος , meaning "dark," and refers to the bluish-gray stems. Members of the genus are commonly known as cliffbrakes...
, including the button fern.
While this group has long been recognized as distinct from the rest of the polypodioid ferns, relationships within the group have long been misunderstood. A ground-breaking paper by Schuettpelz et al. has redefined this order using not only morphological data, but also extensive genetic data. The cladogram at left is based on their data. Line length in this diagram is not meaningful.
Cheilanthes, Pellaea
Pellaea
Pellaea is a genus of ferns in the family Pteridaceae. The name is derived from the Greek word πελλος , meaning "dark," and refers to the bluish-gray stems. Members of the genus are commonly known as cliffbrakes...
, Doryopteris, Jamesonia
Jamesonia
Eriosorus and Jamesonia are two closely related genera in the taenitoid group of the core pteridoid ferns. They have long been recognized as being closely related, and recent genetic evidence has demonstrated that they are both paraphyletic genera, but only in regards to each other...
, Anogramma
Anogramma
Anogramma is a genus of fern in the Pteridaceae family. It contains 8 putative species:* Anogramma ascensionis Diels – endemic to Ascension Island, South Atlantic Ocean.* Anogramma caespitosa – only found on Mount Kilimanjaro, Tanzania....
, and Pteris have all been shown to be seriously paraphyletic genera. Jamesonia
Jamesonia
Eriosorus and Jamesonia are two closely related genera in the taenitoid group of the core pteridoid ferns. They have long been recognized as being closely related, and recent genetic evidence has demonstrated that they are both paraphyletic genera, but only in regards to each other...
and Eriosorus were found to be a highly paraphyletic mixture, although in their own clade. More surprisingly, they found that the vittarioid ferns nest within the genus Adiantum. And they have established that Acrostichum
Acrostichum
Acrostichum was one of the original pteridophyte genera delineated by Linnaeus. It was originally drawn very broadly, including all ferns that had sori apparently "acrostichoid", or distributed in a solid mass across the back of the frond, rather than organized in discrete sori...
and Ceratopteris
Ceratopteris
Ceratopteris is the only genus among homosporous ferns that is exclusively aquatic. It is pan-tropical.-Description:Erect aquatic or subaquatic ferns of moderate size...
are allied within their own isolated clade.
Deriving from the results of this important study, it is clear that the Pteridales should include five distinct families, although their final names are yet to be determined:
- Pellaeaceae (may also be named Sinopteridaceae or Cheilantheaceae): including most of the ferns long recognized as a natural grouping of largely xeric, petrophilic, frequently apogamous small ferns
- AdiantaceaeAdiantaceaeAdiantaceae is a family of ferns in the order Pteridales. This includes the family formerly known as the "Vittariaceae." Recent genetic analyses based on chloroplast genes demonstrate that the vittarioid ferns cladistically nest within the genus Adiantum, making that genus...
(sensu strictu in comparison with past usage): including both rock and terrestrial plants, variously either delicately cut or grass-like - PteridaceaePteridaceaePteridaceae is a large family of ferns in the order Pteridales. Members of the family have creeping or erect rhizomes and are mostly terrestrial or epipetric...
(sensu strictu): including most small to medium sized terrestrial plants - CeratopteridaceaeCeratopteridaceaeCeratopteridaceae is the family name for the clade that is now known to include the two genera Ceratopteris and Acrostichum.Although Ceratopteris was long isolated under its own family, due to adaptations for a dedicated aquatic existence, recent genetic study has determined that these two genera...
(replacing Parkeriaceae which is an invalid name under current rules): exclusively wetland or aquatic ferns (AcrostichumAcrostichumAcrostichum was one of the original pteridophyte genera delineated by Linnaeus. It was originally drawn very broadly, including all ferns that had sori apparently "acrostichoid", or distributed in a solid mass across the back of the frond, rather than organized in discrete sori...
and CeratopterisCeratopterisCeratopteris is the only genus among homosporous ferns that is exclusively aquatic. It is pan-tropical.-Description:Erect aquatic or subaquatic ferns of moderate size...
) - CryptogrammaceaeCryptogrammaceaeCryptogrammaceae is a small family of ferns, which appears to be somewhat isolated from the rest of the Pteridales. This family forms a natural clade that is the most basal to the order. Of these, Llavea is the most basal within the clade....
: largely rock plants, including Llavea, ConiogrammeConiogrammeConiogramme is one of three genera of the fern clade here considered to be Cryptogrammaceae. A cultivated species, Coniogramme pilosa, is known as "bamboo fern."-Species:*Coniogramme affinis Wall. ex Hieron....
, and CryptogrammaCryptogrammaCryptogramma is a genus of ferns known commonly as rockbrakes or parsley ferns. They can be found in temperate regions on several continents worldwide. These ferns have two kinds of leaves which often look so different that at first glance they appear to belong to different plants...