Cyatheaceae
Encyclopedia
The Cyatheaceae is the scaly tree fern family and includes the world's tallest tree ferns, which reach heights up to 20 m. They are also very ancient plants, appearing in the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 record in the late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...

, though the modern genera
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...

 likely appeared in the Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...

. Cyatheaceae is the largest family of tree ferns, including about 500 species. Cyatheaceae and Dicksoniaceae, together with Metaxyaceae and Cibotiaceae, are a monophyletic group and constitute the "core tree ferns." Cyatheaceae are leptosporangiate ferns, the most familiar group of monilophytes.

The Cyatheaceae usually have a single, erect trunk-like rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

 (stem). Their fronds (leaves) are also very large, some of the largest in the plant kingdom. Some species have fronds reaching 3–4 m in length, and have a final crown width of some 6 m. The fronds are circinate
Vernation
Vernation is the formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves in a bud....

 before unfolding and usually pinnately
Pinnate
Pinnate is a term used to describe feather-like or multi-divided features arising from both sides of a common axis in plant or animal structures, and comes from the Latin word pinna meaning "feather", "wing", or "fin". A similar term is pectinate, which refers to a comb-like arrangement of parts...

 or bipinnately compound, with leaflets that are deeply pinnately lobed. The large leaves are covered in scales and hairs and bear 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....

 (spore clusters) on the underside. The sori are often covered by a flap of tissue called an indusium, a useful characteristic for classifying the Cyatheaceae. Some indusia are cup-shaped (cyatheoid), while others are hood-shaped (hemitelioid), enclose the sorus (sphaeropteroid), or scaly. Like most ferns, members of the Cyatheaceae are homosporous. Cyatheaceae are found in both New and Old World tropical wet montane forests and cloud forests, with some species extending into south-temperate regions. Most Cyatheaceae are terrestrial, with one sometimes being epiphytic
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

 and others having a creeping habit, but these are exceptions to the family norm.

Cyatheaceae can be distinguished from arborescent Dicksonia by the presence of scales, the position of the sori, and the morphology of sporangia and spores. In the Cyatheaceae, the 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....

 occur away from the margins of the pinnules, and are elongate or rounded.

Since the exact number of species is not known, classification of the Cyatheaceae has had a long and controversial history, and is still undergoing revision. Three tentative 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...

s
have been developed: Alsophila, Cyathea, and Sphaeropteris. These are frequently used as genus names. Cnemidaria, Trichopteris (or Trichipteris), and Nephelea (or Nephelia) have also been suggested as genera. Initially, indusium and scale morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

 were used to organize the Cyatheaceae into taxonomic rank
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...

s. Most recently, plastid
Plastid
Plastids are major organelles found in the cells of plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell...

 DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 has been used, suggesting that Cyatheaceae should be split into four 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...

s: Sphaeropteris, Cyathea
Cyathea
Cyathea is a genus of tree ferns, the type genus of the fern order Cyatheales. They are mostly terrestrial ferns, usually with a single tall stem. Rarely, the trunk may be branched or creeping. Many species also develop a fibrous mass of roots at the base of the trunk. The genus has a pantropical...

, Alsophila
Cyathea sect. Alsophila
Alsophila is a section in the subgenus Cyathea. The name was originally applied to a genus of tree ferns which is now considered to be syonymous with Cyathea.-Classification:*Subgenus Cyathea**Section Alsophila...

, and Gymnosphaera + A. capensis. However, it remains unclear which of these groups should be considered genera and which are subgenera. These groupings will undoubtedly change as the molecular phylogeny of the Cyatheaceae is refined.

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