Cyatheales
The order Cyatheales is a taxonomic division of the
fern subclass, Cyatheatae, which includes the tree ferns.
In general, any
fern that grows with a trunk elevating the
fronds above ground level can be called a tree fern. However, the plants formally known as tree ferns comprise a group of large ferns belonging to the families
Dicksoniaceae and
Cyatheaceae in the order Cyatheales.
Tree ferns are found growing in tropical and subtropical areas, including cool to temperate
rainforests in
Australia,
New Zealand,
Malaysia,
Lord Howe Island, and other island groups nearby; a few genera extend further, such as
Culcita in southern
Europe.
Encyclopedia
The order
Cyatheales is a taxonomic division of the
fern subclass, Cyatheatae, which includes the
tree ferns.
In general, any
fern that grows with a trunk elevating the
fronds above ground level can be called a tree fern. However, the plants formally known as tree ferns comprise a group of large ferns belonging to the families
Dicksoniaceae and
Cyatheaceae in the order Cyatheales.
Tree ferns are found growing in tropical and subtropical areas, including cool to temperate
rainforests in
Australia,
New Zealand,
Malaysia,
Lord Howe Island, and other island groups nearby; a few genera extend further, such as
Culcita in southern
Europe. Like all ferns, tree ferns reproduce by means of
spores developed in
sporangia on the undersides of the fronds.
The fronds of tree ferns are usually very large and multiple-
pinnate but at least one type has entire fronds. The fronds of tree ferns also exhibit
circinate vernation, meaning the young fronds emerge in coils that uncurl as they grow.
Unlike
flowering plants, tree ferns do not form new woody tissue in their trunk as they grow. Rather, the trunk is supported by a fibrous mass of roots that expands as the tree fern grows.
Some tree fern genera—for example
Dicksonia and
Cibotium, but not
Cyathea—can be transplanted by severing the top portion from the rest of the trunk and replanting it. If the transplanted top part is kept moist it will regrow a new root system over the next year. The success rate of transplantation increases to about 80% if the roots are dug up intact. If the crown of the
Tasmanian tree fern Dicksonia antarctica is damaged, it will die because that is where all new growth occurs. But other clump-forming tree fern species, such as
D. squarrosa and
D. youngiae, can regenerate from basal offsets or from "pups" emerging along the surviving trunk length. Tree ferns often fall over in the wild, yet manage to re-root from this new prostrate position and begin new vertical growth.
It is not certain how many species of tree fern there are but it is likely to be around a thousand. More new species are discovered in New Guinea with each botanical survey. On the other hand, many species have become
extinct in the last century as forest habitats have come under pressure from human intervention.
Other tree ferns
Outside of the Cyatheales a few ferns in other groups could be considered tree ferns, such as several ferns in the family
Osmundaceae that can achieve short trunks under a metre tall and a few species in the genera
Blechnum, Leptopteris, Sadleria and
Todea could also be considered tree ferns in a liberal interpretation of the term.
The families that constitute Cyatheales have been relatively firmly established as a monophyletic clade by
DNA sequencing and morphological studies. The order Plagiogyriales, which contains the family Plagiogyriaceae, is most closely related to the Cyatheales, not to the
Osmundales as had been previously supposed.
References
- Pryer, K.M., A.R. Smith, and J.E. Skog. 1995. Phylogenetic relationships of extant ferns based on evidence from morphology and rbcL sequences. American Fern Journal 85: 205-282.
- Braggins, John E. and Large, Mark F. Tree Ferns. Timber Press .
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