The order Cyatheales, which includes most tree ferns, is a taxonomic order of the fern class, Polypodiopsida. No clear morphological features characterize all of the Cyatheales, but DNA sequence data indicate the order is monophyletic. Some species in the Cyatheales have tree-like growth forms from a vertical rhizome, others have shorter or horizontal expanding rhizomes.

Some species have scales on the stems and leaves, while others have hairs. However, most plants in the Cyatheales are tree ferns and have trunk-like stems up to 10 metres (33 ft) tall. It is unclear how many times the tree form has evolved and been lost in the order.

While the Cyatheales have been shown to be monophyletic through molecular analysis, no prominent morphological characteristics are common to the entire group. Though loosely referred to as "tree ferns", most but not all members of the order possess the characteristic tree fern morphology: the rhizome is massive, woody, and rather than creeping horizontally below or on the ground, it stands erect and above ground, like a tree trunk, bearing a crown of fronds. This habit is most evident in families Dicksoniaceae and Cyatheaceae. Outside of the Cyatheales, a few ferns in other groups could be considered tree ferns, such as several ferns (Leptopteris and Todea) in the family Osmundaceae that can achieve short trunks under 1 metre (3.3 ft) tall. A few species in the genera Blechnum and Sadleria could also be considered tree ferns in a liberal interpretation of the term. ^{[citation needed]}

Like all ferns, tree ferns reproduce by means of spores developed in sporangia on the undersides of the fronds.^{[citation needed]}

The fronds of tree ferns are usually very large and multiple-pinnated, but at least one type has entire (undivided) fronds. The fronds of tree ferns also exhibit circinate vernation, meaning the young fronds emerge in coils that uncurl as they grow.^{[citation needed]}

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.^{[clarification needed]}

Some genera — for example Dicksonia and Cibotium, and some 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 if the roots are dug up intact. If the crown of the Tasmanian tree fern Dicksonia antarctica (the most common species in gardens) is damaged, it will die because all new growth occurs there. 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 reroot from this new prostrate position and begin new vertical growth.^{[citation needed]}

The number of tree fern species is likely to be around a thousand. Although new species are discovered in New Guinea with each botanical survey, many species throughout its range have become extinct in the last century as forest habitats have come under pressure from human activities.^{[citation needed]}