tree fern
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What is a tree fern?
A tree fern is any fern from the order Cyatheales that grows with an ascending trunk-like stem and has a tree-like appearance. These ferns are commonly found in humid tropical forests. They can range in size from a few centimeters to 2 cm to 25 meters in height.
The trunks of tree ferns are composed of rhizomes that grow vertically and are covered by a dense mantle of roots. Their leaves are often highly divided and can reach several meters in length. Tree ferns have a long history, with fossils dating back to the Triassic Period.
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How does a tree fern differ from other ferns?
Tree ferns, mainly from the Cyatheaceae and Dicksoniaceae families, stand out due to their trunklike stems and treelike appearance, setting them apart from other ferns. These ferns are typically found in humid tropical forests and can colonize disturbed habitats.
Unlike trees with bark and wood, tree fern trunks consist of vertically growing rhizomes covered by a dense mantle of roots, reaching heights of 25 meters (80 feet) or more. The most distinct difference between the Cyatheaceae and Dicksoniaceae families lies in their leaves; Cyatheaceae leaves have scales and spines, while Dicksoniaceae leaves are covered in hairs.
While other ferns range from small plants to those 20 meters (65 feet) high, tree ferns are distinct because of their trunk-like stems. Though there is no reliable method for determining the age of ferns, some tree ferns are thought to be several decades old.
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Where are tree ferns commonly found in nature?
Tree ferns are commonly found in humid tropical forests around the world. They can be widespread colonizers of disturbed habitats at lower elevations. Many species have limited ranges on islands or higher elevations, often in mature forests on isolated tropical mountaintops. Ferns in general are most abundant in the tropics, with fewer species in arctic and antarctic regions. A small tropical country like Costa Rica may have over 900 species. They thrive in tropical rainforests, where over 100 species may be found in just a few hectares. Some grow as epiphytes on tree trunks and branches.
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How do tree ferns grow and reproduce?
Tree ferns, found in humid tropical forests, reproduce through a life cycle alternating between sporophyte and gametophyte stages. The mature tree fern (sporophyte) has stems, leaves, and roots, producing spores in sporangia on its leaves. Most tree ferns live for several years and expand vegetatively via rhizomes, forming large colonies.
Spores, dispersed by wind, germinate into tiny gametophytes called prothallia. These prothallia produce sperm and eggs, enabling fertilization. The resulting embryo develops within the prothallium into an independent plant (sporophyte), while the prothallium withers away. Some tree ferns also reproduce vegetatively through root or leaf proliferations.
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What unique features help tree ferns survive in their environment?
Tree ferns, found in humid tropical forests, possess unique features aiding their survival. Their trunks, unlike those of seed plants, consist of vertically growing rhizomes embedded in a dense mantle of adventitious roots, reaching heights of 25 meters or more.
Leaves of Dicksoniaceae are covered in hairs, while Cyatheaceae have scales and spines, especially on petioles. These morphological adaptations, along with their ability to colonize disturbed habitats, contribute to their ecological success. Some species also exhibit structural adaptations to dry habitats, such as thick cuticles and abundant trichomes.
However, overcollection for "orchid bark" and crafting has led to the endangerment of several tree fern species.
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How do people use or protect tree ferns today?
Today, tree ferns are used for horticulture and craftwork, but they face threats from overcollection.
The fibrous root mantle on the trunk is used as "orchid bark" for cultivating orchids and other epiphytes. The trunks are carved into tiki statues and other items for tourists. Cross-sections are crafted into plates and other items.
However, overcollection has led to the rarity of several tree fern species. Many governments now regulate tree fern trade under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), requiring permits for international commerce to protect them.
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tree fern, any of a group of relatively primitive ferns in the order Cyatheales, most of them characterized by ascending trunklike stems and an arborescent (treelike) habit. Tree ferns are conspicuous plants of humid tropical forests around the world. Species found at lower elevations are often widespread colonizers of disturbed or successional habitats. A large number of species are restricted to very small ranges on islands or at higher elevations, often in more-mature forests on isolated tropical mountaintops.
Tree ferns are primarily members of the families Cyatheaceae (five genera) and Dicksoniaceae (three genera) in the division Polypodiophyta. Hypotheses on the classification of tree ferns have evolved as new species and new information on the relationships between genera have been discovered. In addition to the two main families given above, the tree ferns include a few small peripheral relatives: Metaxyaceae, Cibotiaceae, Loxomataceae, Culcitaceae, Plagiogyriaceae, and Thyrsopteridaceae. The most obvious morphological difference between the two larger families is in their leaves. Instead of scales, Dicksoniaceae leaves are covered by various types of hairs, which are especially conspicuous on the petioles. In contrast, Cyatheaceae has scales (and often also sharp spines), especially on the petioles, although hairs also may be present on the leaves.
Instead of the bark and wood that characterize the trunks of seed plant trees, the trunks of tree ferns are composed of rhizomes modified to grow vertically and embedded in a dense mantle of adventitious roots. These trunks may reach heights of 25 metres (80 feet) or more in some species. The growing tip produces a cluster of often highly divided leaves that may reach several metres in length. The sori often have a membranous protective covering (indusium), which can take various forms, including umbrella-shaped, kidney-shaped, and globose. The spores are globose and trilete.
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A number of tree ferns have become quite rare as a result of overcollection by humans. The root mantle on the trunk has been a commercial source of “orchid bark,” a fibrous nonrotting substrate for cultivating orchids and other epiphytic plants. The trunks have been carved into tiki statues and other craft items typically sold to tourists in tropical resorts. The trunk cross sections also produce a beautiful pattern of light and dark tissues originating from the vascular system of the stem and the leaf traces. These have been used for making various handcrafted items, including plates. Finally, a number of species have been collected from the wild for cultivation in greenhouses and conservatories. Governments have responded to these conservation threats by listing most tree ferns under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which prohibits international commerce involving these plants without a special permit.
Tree ferns have a lengthy fossil record stretching back to the Triassic Period (251 to 199.6 million years ago). Members of both Cyatheaceae and Dicksoniaceae appear to have been diverse and relatively common during the succeeding Jurassic Period (199.6 to 145.5 million years ago) and Cretaceous Period (145.5 to 65.5 million years ago). However, the modern genera only become evident during the early Cenozoic (65.5 to 2.6 million years ago). Thus, the tree ferns apparently were affected by the mass extinction event recorded across nearly all groups of organisms at the close of the Cretaceous Period, which opened ecological niches for another period of diversification.