Tree fern
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Tree Fern refers to any fern that grows with a trunk elevating the fronds above ground level. Most tree ferns compose 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 rainforest in Australia, New Zealand and neighbouring regions (eg Malaysia, Lord Howe Island etc). Like all ferns, tree ferns reproduce by means of spores formed on the undersides of the fronds.
The fronds of tree ferns are usually very large and multiple-pinnate. One type, however, has entire (undivided) fronds.
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 species, e.g. Dicksonia and Cibotium, but not Cyathea, can often be transplanted by severing the top portion from the rest of the trunk and replanting it elsewhere. If this transplanted top part is kept moist then 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 Dicksonia antarctica (the commonest species in gardens) is damaged it will inevitably die because that is where all the new growth occurs. But other clump-forming tree fern species, such as Dicksonia 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 postion and begin new vertical growth.
It is not certain how many species of tree fern there are in the world, but it is likely to be around a thousand. New Guinea produces new species every time botanists do a survey. On the other hand, many species have become extinct in the last century as forest habitats have come under pressure from human intervention.
In addition to the Dicksonia and Cyathea species, many ferns in other groups may be considered tree ferns, such as several ferns in the family Osmundaceae, which can achieve short trunks under a metre tall, and particularly ferns in the genus Cibotium, which can grow ten metres tall. Fern species with short trunks in the genera Blechnum, Calochleana, Cnemedaria, Culcita (Europe's only tree fern), Cystodium, Leptopteris, Lophosoria, Sadleria, Thyrsopteris and Todea could also be considered tree ferns in a liberal interpretation of the term.
