Tree ferns are arborescent (tree-like)ferns that grow with atrunk elevating thefronds above ground level, making themtrees. Many extant tree ferns are members of the orderCyatheales, to which belong the familiesCyatheaceae (scaly tree ferns),Dicksoniaceae,Metaxyaceae, andCibotiaceae. It is estimated that Cyatheales originated in the early Jurassic,[1][2] and is the third group of ferns known to have given rise to tree-like forms. The others are the extinctTempskya of uncertain position,[3] andOsmundales where the extinctGuaireaceae and some members ofOsmundaceae also grew into trees. In addition there were thePsaroniaceae includingTietea in theMarattiales, which is the sister group to all theleptosporangiate ferns.[4]
Other tree ferns includeLeptopteris andTodea in the family Osmundaceae, which can achieve short trunks under a metre tall.Osmunda regalis is sometimes considered a tree fern.[5] Fern species with short trunks in the generaBlechnum,Cystodium andSadleria from the orderPolypodiales and smaller members of Cyatheales likeCalochlaena,Cnemedaria,Culcita,Lophosoria andThyrsopteris are also considered tree ferns. The speciesCtenitis sloanei (Florida tree fern) from Florida, Mexico, Bermuda and the Caribbean is sometimes called a tree fern.[6][7][8][9] Like all ferns, tree ferns reproduce by means ofspores formed on the undersides of the fronds.
Tree ferns are found growing in tropical and subtropical areas worldwide, as well as cool to temperaterainforests inAustralia,New Zealand and neighbouring regions (e.g.Lord Howe Island, Norfolk Island, Nuie etc.). They are also found in New Caledonia. In the Americas, they are widespread in Colombia, Ecuador, Brazil, Argentina, Chile, Bolivia, El Salvador, Honduras, Nicaragua, Peru, Brazil, Mexico, Costa Rica, Panama, Guatemala, Cuba, Puerto Rico, and other Caribbean islands as well as many of the islands near South America.[5] A single tree fern is known to exist in the mainland United States and the Bahamas. Tree ferns are common place in most Pacific islands like the Clipperton Islands, Cocos Islands, Revillagigedo Islands, Hawaiian Islands, Johnston Atoll, Wake Island, Marcus Island (Minami-Tori-shima), Northern Mariana Islands, Guam, Palau, Federated States of Micronesia (Yap, Chuuk, Pohnpei, Kosrae), Marshall Islands (Bikini, Enewetak, Majuro, Kwajalein), Nauru, Kiribati (Gilbert Islands, Phoenix Islands, Line Islands), Tuvalu, Tokelau, Wallis and Futuna, American Samoa, Samoa, Tonga, Cook Islands, French Polynesia (Marquesas, Tuamotu, Gambier, Society, Austral Islands), Pitcairn Islands, Easter Island (Rapa Nui).[5] Tree ferns are known from Indonesia, Timor, Malaysia, Papua New Guinea, Thailand, Myanmar, Vietnam, Cambodia, The Philippines, Japan, China, Laos, India, Bangladesh and some nearby islands such as the Andaman and Nicobar Islands.[5] In Africa, they can be found in places such as Kenya, Tanzania, Uganda, South Africa, Mozambique, Zimbabwe, Zambia, Malawi, Comoros, Seychelles and Madagascar.[5] In Europe they are mainly known from Iberia in places such as Spain, Portugal and the Canary Islands.[5]
The fronds of tree ferns are usually very large and multiple-pinnate. Their trunk is actually a vertical and modifiedrhizome,[10] andwoody tissue is absent. To add strength, there are deposits oflignin in the cell walls and the lower part of the stem is reinforced with thick, interlocking mats of tiny roots.[11] If thecrown ofDicksonia antarctica (the most common 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 asD. squarrosa andD. 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.[citation needed]
Tree-ferns have been cultivated for their beauty alone; a few, however, were of some economic application, chiefly as sources of starch. These include theSphaeropteris excelsa ofNorfolk Island that was threatened with extinction for the sake of itssago-likepith, which was eaten by pigs. It is now widely cultivated as an ornamental tree, although there is only one small wild population on Norfolk Island.[12]Sphaeropteris medullaris (mamaku, black tree fern) also furnished a kind of sago to people living in New Zealand, Queensland and the Pacific islands. AJavanese species ofDicksonia (D. chrysotricha) furnishes silky hairs, which were once imported as astyptic, and the long silky or wooly hairs, abundant on the stem and frond-leaves in the various species ofCibotium have not only been put to a similar use, but in theHawaiian Islands furnished wool for stuffing mattresses and cushions, which was formerly an article of export.[13]
It is not certain the exact number of species of tree ferns there are, but it may be close to 600–700 species.[14] Many species have becomeextinct in the last century as forest habitats have come under pressure from human intervention.[citation needed]
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One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Tree-Fern".Encyclopædia Britannica. Vol. 27 (11th ed.). Cambridge University Press. p. 235.