Tallest fern

The title of tallest fern is shared by two species of Australasian tree fern: the Norfolk tree fern (Cyathea brownii = Sphaeropteris excelsa), native to Norfolk Island, situated between Australia and New Zealand in the Pacific Ocean; and the rough tree fern (C. australis = Alsophila australis), native to mainland Australia, Tasmania and Norfolk Island. Both of them have been recorded attaining a total height of up to 20 m (65 ft), with a few unconfirmed accounts even claiming taller than this. Their individual fronds can reach in excess of 3 m (9 ft 10 in) long.

Tree ferns are so named because whereas more familiar ferns sport fronds that remain at ground level, tree ferns develop a thick vertical tree-like trunk (but actually a modified rhizome) that sports its fronds at a considerable height above ground level, thereby paralleling true trees and their branches. Consequently, tree ferns are technically said to be "arborescent" (tree-like) in structure.

C. australis is called the rough tree fern because its trunk is covered in tubercles, scales and adventitious roots, thus making its texture particularly rough to the touch.