Tree fern (Cyatheales)
Dicksonia antarctica
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Polypodiopsida /  Pteridopsida (disputed)
Order:	Cyatheales
Families and Genera
Thyrsopteridaceae Thyrsopteris Loxsomataceae Loxsoma Loxsomopsis Culcitaceae Culcita Plagiogyriaceae Plagiogyria Cibotiaceae Cibotium Cyatheaceae Alsophila Cyathea Gymnosphaera Hymenophyllopsis Sphaeropteris Dicksoniaceae Calochlaena Dicksonia Lophosoria Metaxyaceae Metaxya

The order Cyatheales, which includes the tree ferns, is a taxonomic division of the fern class, Polypodiopsida.^[1] No clear morphological features characterize all of the Cyatheales, but DNA sequence data indicates that the order is monophyletic. Some species in the Cyatheales have tree-like growth forms, but others have creeping rhizomes (stems). 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 20 meters tall. It is unclear how many times the tree form has evolved and been lost in the order.^[2]

Description[link]

In general, any fern that grows with a trunk elevating the fronds (leaves) above ground level can be called a tree fern. However, the plants formally known as tree ferns comprise 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 as well as temperate rainforests in Australia, New Zealand, and other island groups nearby; a few genera extend further, such as Culcita in southern Europe. Like all ferns, tree ferns reproduce by means of spores developed in sporangia on the undersides of the fronds.

Tasmanian tree fern (Dicksonia antarctica) in an English garden. The trunk is 60 cm (24 in) high.

The fronds of tree ferns are usually very large and multiple-pinnate 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.

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 genera — for example Dicksonia and Cibotium, but not 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 to about 80% 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 that is where all new growth occurs. 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 re-root from this new prostrate position and begin new vertical growth.

Tree fern frond ("fiddlehead") by the Akatarawa River, New Zealand. These unopened fronds are edible but must be roasted first to remove shikimic acid.

It is not certain how many species of tree fern there are but it 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 intervention.

Threats to tree ferns[link]

While many ferns are able to achieve a widespread distribution because of their spore reproduction, tree fern species tend to be very local. This makes their species much more susceptible to the effects of local deforestation. It is not known why species are not more widespread, especially considering that they have sufficient height to have a greater chance of getting spore into the wind stream.^{[citation needed]}

Where feral pigs are a problem, such as in some Hawaiian rainforests, they will knock over tree ferns to root out the starchy pith, killing the plant.^[3]

Non-Cyatheales tree ferns[link]

Outside of the Cyatheales a few ferns in other groups could be considered tree ferns, such as several ferns in the family Osmundaceae that can achieve short trunks under 1 metre (3.3 ft) tall. A few species in the genera Blechnum, Leptopteris, Sadleria and Todea could also be considered tree ferns in a liberal interpretation of the term.

The families that constitute Cyatheales have been relatively firmly established as a clade by DNA sequencing and morphological studies. The order Plagiogyriales, which contains the family Plagiogyriaceae, is most closely related to the Cyatheales, not to the Osmundales as had been previously supposed.

Transplanted Dicksonia antarctica tree ferns at Combe Martin Wildlife and Dinosaur Park, Devon, England.

Phylogeny[link]

The following phylogram shows a possible relationship between the Cyatheales families and their genera.^[4][1][5]

References[link]

• Pryer, K.M., A.R. Smith, and J.E. Skog. 1995. Phylogenetic relationships of extant ferns based on evidence from morphology and rbcL sequences. American Fern Journal 85: 205-282.
• C.Michael Hogan. 2010. Fern. Encyclopedia of Earth. National council for Science and the Environment. Washington, DC
• Large, M.F. and J.E. Braggins Tree Ferns. Timber Press (2004).
• Smith, A.R., K.M. Pryer, E. Schuettpelz, P. Korall, H. Schneider & P.G. Wolf 2006. A classification for extant ferns.PDF (420 KiB) Taxonomy 55(3): 705-731.

External links[link]

• Community: Care and propagation of Treeferns (German/English)
• Fern Files: Tree Ferns

Wikimedia Commons has media related to: Cyatheales

Trees on a mountain in northern Utah during early autumn

Trunk base of a Coast Redwood tree in Jedediah Smith Redwoods State Park: Simpson Reed Discovery Trail, near Crescent City, California

A tree is a perennial woody plant. It most often has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance.^[1] A minimum height specification at maturity is cited by some authors, varying from 3 m^[2] to 6 m;^[3] some authors set a minimum of 10 cm trunk diameter (30 cm girth).^[4] Woody plants that do not meet these definitions by having multiple stems and/or small size are usually called shrubs, although many trees such as Mallee do not meet such definitions. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (379 ft) high.^[5]

Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. They also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples). Wood from trees is a building material, as well as a primary energy source in many developing countries. Trees also play a role in many of the world's mythologies (see trees in mythology).^[6]

Classification[link]

A tree is a plant form that occurs in many different orders and families of plants. Most species of trees today are flowering plants (angiosperms) and conifers. Trees show a variety of growth forms, leaf type and shape, bark characteristics and reproductive organs. For the listing of examples of well-known trees and how they are classified, see List of tree genera.

The tree form has evolved separately in unrelated classes of plants, in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimate of 100,000 tree species, the number of tree species worldwide might total 25 percent of all living plant species.^[7] The majority of tree species grow in tropical regions of the world and many of these areas have not been surveyed yet by botanists, making species diversity and ranges poorly understood.^[8] The earliest tree-like organisms were tree ferns, horsetails and lycophytes, which grew in forests in the Carboniferous period, however these plants were not trees^{[citation needed]}, since they lacked woody tissue. Trees evolved in the Triassic period, with conifers, ginkgos, cycads and other gymnosperms appeared producing woody tissue, and were subsequently followed by tree-form flowering plants in the Cretaceous period.

A small group of trees growing together is called a grove or copse, and a landscape covered by a dense growth of trees is called a forest. Several biotopes are defined largely by the trees that inhabit them; examples are rainforest and taiga (see ecozones). A landscape of trees scattered or spaced across grassland (usually grazed or burned over periodically) is called a savanna. A forest of great age is called old growth forest or ancient woodland (in the UK). A young tree is called a sapling.

Morphology[link]

Tree roots anchor the structure and provide water and nutrients. The ground has eroded away around the roots of this young red pine tree.

Many trees show strong apical dominance.

The parts of a tree are the roots, trunk(s), branches, twigs and leaves. Tree stems consist mainly of support and transport tissues (xylem and phloem). Wood consists of xylem cells, and bark is made of phloem and other tissues external to the vascular cambium. Trees may be grouped into exogenous and endogenous trees according to the way in which their stem diameter increases. Exogenous trees, which comprise the great majority of trees (all conifers, and almost all broadleaf trees), grow by the addition of new wood outwards, immediately under the bark. Endogenous trees, mainly in the monocotyledons (e.g., aloes and dragon trees), grow by addition of new material as discrete bundles within the existing trunk tissue.

Trees can be identified to genus or species by a combination of the tree's shape, and the characteristics of its bark, leaves, flowers, and fruit. The leaves may be either deciduous or evergreen.^[2][3]

As an exogenous tree grows, it creates growth rings as new wood is laid down concentrically over the old wood. In species growing in areas with seasonal climate changes, wood growth produced at different times of the year may be visible as alternating light and dark, or soft and hard, rings of wood.^[3] In temperate climates, and tropical climates with a single wet-dry season alternation, the growth rings are annual, each pair of light and dark rings being one year of growth; these are known as annual rings. In areas with two wet and dry seasons each year, there may be two pairs of light and dark rings each year; and in some (mainly semi-desert regions with irregular rainfall), there may be a new growth ring with each rainfall.^[9] In tropical rainforest regions, with constant year-round climate, growth is continuous and the growth rings are not visible nor is there a change in the wood texture. In species with annual rings, these rings can be counted to determine the age of the tree, and used to date cores or even wood taken from trees in the past, a practice known as the science of dendrochronology. Very few tropical trees can be accurately dated in this manner. Age determination in this manner is also impossible in endogenous trees.

The roots of a tree are generally embedded in earth, providing anchorage for the above-ground biomass and absorbing water and nutrients from the soil. However, while ground nutrients are essential to a tree's growth the majority of its biomass – over 90 percent – comes from carbon dioxide absorbed from the atmosphere (see photosynthesis).^[10] Above ground, the trunk gives height to the leaf-bearing branches, aiding in competition with other plant species for sunlight. In many trees, the arrangement of the branches optimizes exposure of the leaves to sunlight.

Not all trees have all the plant organs or parts mentioned above. For example, the saguaro cactus of North America has no functional leaves. A plant form that is similar to a tree, but generally having smaller, multiple trunks and/or branches that arise near the ground, is called a shrub. However, no precise differentiation between shrubs and trees is possible. Given their small size, bonsai plants would not technically be "trees", but one should not confuse reference to the form of a species with the size or shape of individual specimens. A spruce seedling does not fit the definition of a tree, but all spruces are trees.

Record breaking trees[link]

The world's champion trees can be rated on height, trunk diameter or girth, total size, and age.

Tallest trees[link]

The coniferous Coast Redwood is the tallest tree species on earth.

The heights of the tallest trees in the world have been the subject of considerable dispute and much exaggeration. Modern verified measurements with laser rangefinders, or with tape drop measurements made by tree climbers (such as those carried out by canopy researchers or members of groups like the Native Tree Society), have shown that some older measuring methods and measurements are often unreliable, sometimes producing exaggerations of 5% to 15% or more above the real height. Historical claims of trees growing to 130 m (430 ft), and even 150 m (490 ft), are now largely disregarded as unreliable, and attributed to human error. Historical records of fallen trees measured prostrate on the ground are considered to be somewhat more reliable. The following are now accepted as the top nine tallest reliably measured species (taken only currently standing specimens):

1. Coast Redwood (Sequoia sempervirens): 115.66 m (379.46 ft), Hyperion, Redwood National Park, California, United States^[11]
2. Coast Douglas-fir (Pseudotsuga menziesii): 99.76 m (327.3 ft), Brummit Creek, Coos County, Oregon, United States^[12]
3. Australian Mountain Ash (Eucalyptus regnans): 99.6 m (327 ft), south of Hobart, Tasmania, Australia^[13]
4. Sitka Spruce (Picea sitchensis): 96.7 m (317 ft), Prairie Creek Redwoods State Park, California, United States^[14]
5. Giant Sequoia (Sequoiadendron giganteum): 95.8 m (314 ft), Sequoia National Forest, California, United States^[15]
6. Tasmanian Blue Gum (Eucalyptus globulus): 90.7 m (298 ft), Tasmania, Australia^[16]
7. Manna Gum (Eucalyptus viminalis): 89 m (292 ft), Evercreech Forest Reserve, Tasmania, Australia^[16]
8. Shorea faguetiana: 88.3 m (290 ft) Tawau Hills National Park, in Sabah on the island of Borneo^[17]
9. Alpine Ash (Eucalyptus delegatensis): 87.9 m (288 ft), Tasmania, Australia^[16]

A view of a tree from below; this may exaggerate apparent height

Stoutest trees[link]

The girth of a tree is usually much easier to measure than the height, as it is a simple matter of stretching a tape round the trunk, and pulling it taut to find the circumference. Despite this, UK tree author Alan Mitchell made the following comment about measurements of yew trees:

The aberrations of past measurements of yews are beyond belief. For example, the tree at Tisbury has a well-defined, clean, if irregular bole at least 1.5 m long. It has been found to have a girth that dilated and shrunk in the following way: 11.28 m (1834 Loudon), 9.3 m (1892 Lowe), 10.67 m (1903 Elwes and Henry), 9.0 m (1924 E. Swanton), 9.45 m (1959 Mitchell) ... Earlier measurements have therefore been omitted.

As a general standard, tree girth is taken at "breast height". This is cited as dbh (diameter at breast height) in tree and forestry literature.^[3][18] Breast height is defined differently in different situations, with most forestry measurements taking girth at 1.3 m above ground,^[18] while those who measure ornamental trees usually measure at 1.5 m above ground;^[3] in most cases this makes little difference to the measured girth. On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk^[3][18], but in North America a point, that is the average of the highest point and the lowest point the tree trunk appears to contact the soil, is usually used.^[19] Some of the inflated old measurements may have been taken at ground level. Some past exaggerated measurements also result from measuring the complete next-to-bark measurement, pushing the tape in and out over every crevice and buttress.^[20]

Modern trends are to cite the tree's diameter rather than the circumference. Diameter of the tree is calculated by finding the medium diameter of the trunk, in most cases obtained by dividing the measured circumference by π; this assumes the trunk is mostly circular in cross-section (an oval or irregular cross-section would result in a mean diameter slightly greater than the assumed circle). Accurately measuring circumference or diameter is difficult in species with the large buttresses that are especially characteristic in many species of rainforest trees. Simple measurement of circumference of such trees can be misleading when the circumference includes much empty space between buttresses.

One further problem with measuring baobabs Adansonia is that these trees store large amounts of water in the very soft wood in their trunks. This leads to marked variation in their girth over the year (though not more than about 2.5%^[21]), swelling to a maximum at the end of the rainy season, minimum at the end of the dry season.

The stoutest living single-trunk species in diameter are:

1. Montezuma Cypress Taxodium mucronatum: 11.62 m (38.1 ft), Árbol del Tule, Santa Maria del Tule, Oaxaca, Mexico.^[22] Note though that this diameter includes buttressing; the actual idealised diameter of the area of its wood is 9.38 m (30.8 ft).^[22]
2. Giant Sequoia Sequoiadendron giganteum: 8.85 m (29.0 ft), General Grant tree, General Grant Grove, California, United States^[23]
3. Coast Redwood Sequoia sempervirens: 7.9 m (26 ft), Lost Monarch Jedediah Smith Redwoods State Park, California, United States.
4. Australian Oak Eucalyptus obliqua: 6.72 m (22.0 ft)
5. Australian Mountain Ash Eucalyptus regnans: 6.52 m (21.4 ft), Big Foot
6. Western Redcedar Thuja plicata: 5.99 m (19.7 ft), Kalaloch Cedar, Olympic National Park
7. Sitka Spruce Picea sitchensis: 5.39 m (17.7 ft), Quinalt Lake Spruce, Olympic National Park
8. Kauri Agathis australis (Te Matua Ngahere): 5.33 m (17.5 ft).^[24]
9. Alerce Fitzroya cupressoides: 5.0 m (16.4 ft)

An additional problem lies in instances where multiple trunks (whether from an individual tree or multiple trees) grow together. The Sacred Fig is a notable example of this, forming additional "trunks" by growing adventitious roots down from the branches, which then thicken up when the root reaches the ground to form new trunks; a single Sacred Fig tree can have hundreds of such trunks.^[1] The multi-stemmed Hundred Horse Chestnut was known to have a circumference of 57.9 m (190 ft) when it was measured in 1780.

Largest trees[link]

General Sherman is the largest tree on Earth

The largest trees in total volume are both tall and large in diameter and, in particular, hold a large diameter high up the trunk. Measurement is very complex, particularly if branch volume is to be included as well as the trunk volume, so measurements have only been made for a small number of trees, and generally only for the trunk. No attempt has ever been made to include root volume. Measuring standards vary.

The top ten species measured so far are*:

1. Giant Sequoia Sequoiadendron giganteum: 1,487 m³ (52,508 cu ft), General Sherman^[25]
2. Coast Redwood Sequoia sempervirens: 1,203 m³ (42,500 cu ft), Lost Monarch^[26]
3. Montezuma Cypress Taxodium mucronatum: 750 m³ (25,000 cu ft), Árbol del Tule^[27]
4. Kauri Agathis australis (Tāne Mahuta): 516 m³ ^[28]
5. Western Redcedar Thuja plicata: 500 m³ (17,650 cu ft ), Quinault Lake Redcedar^[25]
6. Tasmanian Blue Gum Eucalyptus globulus: 368 m³ (13,000 cu ft), Rullah Longatyle (Strong Girl, also Grieving Giant) ^[16]
7. Australian Mountain Ash Eucalyptus regnans: 360 m³ (12,714 cu ft), Arve Big Tree^[16]
8. Coast Douglas-fir Pseudotsuga menziesii 349 m³ (12,320 cu ft) Red Creek Tree
9. Sitka Spruce Picea sitchensis 337 m³ (11,920 cu ft) Queets Spruce^[29]
10. Australian Oak Eucalyptus obliqua: 337 m³ (11,920 cu ft) Gothmog^[16]
11. Alpine Ash Eucalyptus delegatensis: 286 m³ (10,100 cu ft), located in Styx River Valley^[16]

(*)This list does not take into account now dead specimens.

Oldest trees[link]

The oldest trees are determined by growth rings, which can be seen if the tree is cut down, or in cores taken from the bark to the center of the tree. Accurate determination is only possible for trees that produce growth rings, generally those in seasonal climates. Trees in uniform non-seasonal tropical climates grow continuously and do not have distinct growth rings. It is also only possible for trees that are solid to the center. Many very old trees become hollow as the dead heartwood decays. For some of these species, age estimates have been made on the basis of extrapolating current growth rates, but the results are usually largely speculation. White (1998)^[30] proposes a method of estimating the age of large and veteran trees in the United Kingdom through the correlation between a tree's stem diameter, growth character and age.

The verified oldest measured ages are:

1. Great Basin Bristlecone Pine (Methuselah) Pinus longaeva: 4,844 years^[31]
2. Alerce Fitzroya cupressoides: 3,622 years^[31]
3. Giant Sequoia Sequoiadendron giganteum: 3,266 years^[31]
4. Sugi Cryptomeria japonica: 3,000 years^[32]
5. Huon-pine Lagarostrobos franklinii: 2,500 years^[31]

Other species suspected of reaching exceptional age include European Yew Taxus baccata (probably over 2,000 years^[33][34]) and Western Redcedar Thuja plicata. The oldest known European Yew is the Llangernyw Yew in the Churchyard of Llangernyw village in North Wales, which is estimated to be between 4,000 and 5,000 years old.

Damage[link]

El Grande, about 85 m (279 ft) high, the most massive (though not the tallest) Eucalyptus regnans was accidentally killed by loggers burning-off the remains of legally loggable trees (less than 85 m) that had been felled all around it.

Callus growth on beech branch following fire (heat) damage.

The two sources of tree damage are either biotic (from living sources) or abiotic (from non-living sources). Biotic sources include insects that bore into the tree, deer that rub bark off, and fungi.^[35]

Abiotic sources include lightning, vehicles impacts, and construction activities. Construction activities can involve a number of damage sources, including grade changes that prevent aeration to roots, spills involving toxic chemicals such as cement or petroleum products, or severing of branches or roots.

Both damage sources can result in trees becoming dangerous, and the term "hazard trees" is commonly used by arborists, and industry groups such as power line operators. Hazard trees are trees that, due to disease or other factors, are more susceptible to falling in windstorms, or having parts of the tree fall.

Evaluating the danger a tree presents is based on a process called the Quantified Tree Risk Assessment.^[36]

Assessment as to labeling a tree a hazard tree can be based on a field examination. Assessment as a result of construction activities that will damage a tree is based on three factors: severity, extent and duration. Severity relates usually to the degree of intrusion into the TPZ and resultant root loss. Extent is frequently a percentage of a factor such as canopy, roots or bark, and duration is normally based on time. Root severing is considered permanent in time.

Trees are similar to people. Both can withstand massive amounts of some types of damage and survive, but even small amounts of certain types of trauma can result in death. Arborists are very aware that established trees will not tolerate any appreciable disturbance of the root system.^[37] However, lay people and construction professionals seldom recognise how easily a tree can be killed.

One reason for confusion about tree damage from construction involves the dormancy of trees during winter. Another factor is that trees may not show symptoms of damage until two years or longer after damage has occurred. For that reason, persons uneducated in arboricultural science may not correlate the actual cause and resultant effect.

Various organisations, such as the International Society of Arboriculture, the British Standards Institute and the Tree Industry Association (formerly the National Arborist Association), have long recognised the importance of construction activities that impact tree health. The impacts are important because they can result in monetary losses due to tree damage and resultant remediation or replacement costs, as well as violation of government ordinances or community or subdivision restrictions.

As a result, protocols for tree management prior to, during and after construction activities are well established, tested and refined. These basic steps are involved:

• Review of the construction plans
• Development of the related tree inventory
• Application of standard construction tree management protocols
• Assessment of potential for expected tree damages
• Development of a tree protection plan (providing for pre-, concurrent, and post construction damage prevention and remediation steps)
• Development of a tree protection plan
• Development of a remediation plan
• Implementation of tree protection zones (TPZ)
• Assessment of construction tree damage, post-construction
• Implementation of the remediation plan

The shield of Currier House (Harvard College).

Trees in culture[link]

The tree has always been a cultural symbol. Common icons are the World tree, for instance Yggdrasil,^[38] and the tree of life. The tree is often used to represent nature or the environment itself.

The tree is also a symbol and mascot for Stanford University and Currier House (Harvard College).

Tree value approximation (USA)[link]

Studies have shown that trees contribute as much as 27% of the appraised land value in certain markets and cite the following^[39] which can be extrapolated with care.

These most likely use diameter measured at breast height, 4.5 feet (140 cm) above ground, not the larger base diameter. A general model for any year and diameter is Value = 17.27939*(diameter^2)*1.022^(year-1985) assuming 2.2% inflation per year.^[41] The right side of this equation is written to paste into Excel or Google to perform the calculation. Extrapolations from any model can vary widely, so value estimates for diameters larger than 30 inches (760 mm) may have to be capped so trees do not exceed 27% of total appraised land value.

See also[link]

References[link]

Notes[link]

Bibliography[link]

• Pakenham, T. (2002). Remarkable Trees of the World. ISBN 0-297-84300-1
• Pakenham, T. (1996). Meetings with Remarkable Trees. ISBN 0-297-83255-7
• Tudge, C. (2005). The Secret Life of Trees. How They Live and Why They Matter. Allen Lane. London. ISBN 0-7139-9698-6

External links[link]

Trees portal

Wikimedia Commons has media related to: Trees

Look up tree in Wiktionary, the free dictionary.

• Gymnosperm database
• Silvics of North America
• University of Florida's Landscape Plants website
• Global Trees Campaign (campaigning to save the world's most threatened trees)
• International Society of Arboriculture
• Eastern Native Tree Society
• Western Native Tree Society
• Trees The Arbor Day Foundation
• Tree Encyclopedia Extensive collection of diagnostic photos, Morton Arboretum Specimens
• Wondermondo - Trees Largest and most unusual trees of the world
• Venerable Trees Venerable trees of the planet

lez:Ттарvep:Pu

Ferns (Pteridophyta) Temporal range: Mid Devonian[1]—Recent PreЄ Є O S D C P T J K Pg N
Athyrium filix-femina unrolling young frond
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Classes[2]
†Cladoxylopsida Psilotopsida Equisetopsida (alias Sphenopsida) Marattiopsida Polypodiopsida (alias Pteridopsida, Filicopsida) †Zygopteridales †Stauropteridales †Rhacophytales

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta.^[3] Unlike mosses, they have xylem and phloem (making them vascular plants). They have stems, leaves, and roots like other vascular plants. Ferns reproduce via spores and have neither seeds nor flowers.

By far the largest group of ferns are the leptosporangiate ferns, but ferns as defined here (also called monilophytes) include horsetails, whisk ferns, marattioid ferns, and ophioglossoid ferns. The term pteridophyte also refers to ferns and a few other seedless vascular plants (see classification section below).

Ferns first appear in the fossil record 360 million years ago in the Carboniferous but many of the current families and species did not appear until roughly 145 million years ago in the early Cretaceous (after flowering plants came to dominate many environments).

Ferns are not of major economic importance, but some are grown or gathered for food, as ornamental plants, for remediating contaminated soils, and have been the subject of research for their ability to remove some chemical pollutants from the air. Some are significant weeds. They also play a role in mythology, medicine, and art.

Life cycle[link]

Gametophyte (thalloid green mass) and sporophyte (ascendent frond) of Onoclea sensibilis

Ferns are vascular plants differing from lycophytes by having true leaves (megaphylls), which are often pinnate. They differ from seed plants (gymnosperms and angiosperms) in their mode of reproduction—lacking flowers and seeds. Like all other vascular plants, they have a life cycle referred to as alternation of generations, characterized by alternating diploid sporophytic and haploid gametophytic phases. The diploid sporophyte has 2n paired chromosomes, where n varies from species to species. The haploid gametophyte has n unpaired chromosomes, i.e. half the number of the sporophyte. Unlike the gymnosperms and angiosperms, the ferns' gametophyte is a free-living organism.

Life cycle of a typical fern:

1. A diploid sporophyte phase produces haploid spores by meiosis (a process of cell division which reduces the number of chromosomes by a half).
2. A spore grows into a haploid gametophyte by mitosis (a process of cell division which maintains the number of chromosomes). The gametophyte typically consists of a photosynthetic prothallus.
3. The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis.
4. A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus.
5. The fertilized egg is now a diploid zygote and grows by mitosis into a diploid sporophyte (the typical "fern" plant).

Fern ecology[link]

Ferns at Muir Woods, California

The stereotypic image of ferns growing in moist shady woodland nooks is far from being a complete picture of the habitats where ferns can be found growing. Fern species live in a wide variety of habitats, from remote mountain elevations, to dry desert rock faces, to bodies of water or in open fields. Ferns in general may be thought of as largely being specialists in marginal habitats, often succeeding in places where various environmental factors limit the success of flowering plants. Some ferns are among the world's most serious weed species, including the bracken fern growing in the Scottish highlands, or the mosquito fern (Azolla) growing in tropical lakes, both species forming large aggressively spreading colonies. There are four particular types of habitats that ferns are found in: moist, shady forests; crevices in rock faces, especially when sheltered from the full sun; acid wetlands including bogs and swamps; and tropical trees, where many species are epiphytes (something like a quarter to a third of all fern species^[4]).

Many ferns depend on associations with mycorrhizal fungi. Many ferns only grow within specific pH ranges; for instance, the climbing fern (Lygodium) of eastern North America will only grow in moist, intensely acid soils, while the bulblet bladder fern (Cystopteris bulbifera), with an overlapping range, is only found on limestone.

The spores are rich in lipids, protein and calories, so some vertebrates eat these. The European woodmouse (Apodemus sylvaticus) has been found to eat the spores of Culcita macrocarpa and the bullfinch (Pyrrhula murina) and the New Zealand lesser short-tailed bat (Mystacina tuberculata) also eat fern spores.^[5]

Fern structure[link]

Ferns at the Royal Melbourne Botanical Gardens

Tree ferns, probably Dicksonia antarctica, growing in Nunniong, Australia

Like the sporophytes of seed plants, those of ferns consist of:

• Stems: Most often an underground creeping rhizome, but sometimes an above-ground creeping stolon (e.g., Polypodiaceae), or an above-ground erect semi-woody trunk (e.g., Cyatheaceae) reaching up to 20 m in a few species (e.g., Cyathea brownii on Norfolk Island and Cyathea medullaris in New Zealand).
• Leaf: The green, photosynthetic part of the plant. In ferns, it is often referred to as a frond, but this is because of the historical division between people who study ferns and people who study seed plants, rather than because of differences in structure. New leaves typically expand by the unrolling of a tight spiral called a crozier or fiddlehead. This uncurling of the leaf is termed circinate vernation. Leaves are divided into three types:
  • Trophophyll: A leaf that does not produce spores, instead only producing sugars by photosynthesis. Analogous to the typical green leaves of seed plants.
  • Sporophyll: A leaf that produces spores. These leaves are analogous to the scales of pine cones or to stamens and pistil in gymnosperms and angiosperms, respectively. Unlike the seed plants, however, the sporophylls of ferns are typically not very specialized, looking similar to trophophylls and producing sugars by photosynthesis as the trophophylls do.
  • Brophophyll: A leaf that produces abnormally large amounts of spores. Their leaves are also larger than the other leaves but bear a resemblance to trophophylls.
• Roots: The underground non-photosynthetic structures that take up water and nutrients from soil. They are always fibrous and are structurally very similar to the roots of seed plants.

The gametophytes of ferns, however, are very different from those of seed plants. They typically consist of:

• Prothallus: A green, photosynthetic structure that is one cell thick, usually heart or kidney shaped, 3–10 mm long and 2–8 mm broad. The prothallus produces gametes by means of:
  • Antheridia: Small spherical structures that produce flagellate sperm.
  • Archegonia: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck.
• Rhizoids: root-like structures (not true roots) that consist of single greatly elongated cells, water and mineral salts are absorbed over the whole structure. Rhizoids anchor the prothallus to the soil.

One difference between sporophytes and gametophytes might be summed up by the saying that "Nothing eats ferns, but everything eats gametophytes." This is an over-simplification, but it is true that gametophytes are often difficult to find in the field because they are far more likely to be food than are the sporophytes.

Evolution and classification[link]

Ferns first appear in the fossil record in the early-Carboniferous period. By the Triassic, the first evidence of ferns related to several modern families appeared. The "great fern radiation" occurred in the late-Cretaceous, when many modern families of ferns first appeared.

One problem with fern classification is the problem of cryptic species. A cryptic species is a species that is morphologically similar to another species, but differs genetically in ways that prevent fertile interbreeding. A good example of this is the currently designated species Asplenium trichomanes, the maidenhair spleenwort. This is actually a species complex that includes distinct diploid and tetraploid races. There are minor but unclear morphological differences between the two groups, which prefer distinctly differing habitats. In many cases such as this, the species complexes have been separated into separate species, thus raising the number of overall fern species. Possibly many more cryptic species are yet to be discovered and designated.

Ferns have traditionally been grouped in the Class Filices, but modern classifications assign them their own phylum or division in the plant kingdom, called Pteridophyta, also known as Filicophyta. The group is also referred to as Polypodiophyta, (or Polypodiopsida when treated as a subdivision of tracheophyta (vascular plants), although Polypodiopsida sometimes refers to only the leptosporangiate ferns). The term "pteridophyte" has traditionally been used to describe all seedless vascular plants, making it synonymous with "ferns and fern allies". This can be confusing since members of the fern phylum Pteridophyta are also sometimes referred to as pteridophytes.

Traditionally, three discrete groups of plants have been considered ferns: two groups of eusporangiate ferns—families Ophioglossaceae (adders-tongues, moonworts, and grape-ferns) and Marattiaceae—and the leptosporangiate ferns. The Marattiaceae are a primitive group of tropical ferns with a large, fleshy rhizome, and are now thought to be a sibling taxon to the main group of ferns, the leptosporangiate ferns. Several other groups of plants were considered "fern allies": the clubmosses, spikemosses, and quillworts in the Lycopodiophyta, the whisk ferns in Psilotaceae, and the horsetails in the Equisetaceae. More recent genetic studies have shown that the Lycopodiophyta are more distantly related to other vascular plants, having radiated evolutionarily at the base of the vascular plant clade, while both the whisk ferns and horsetails are as much "true" ferns as are the Ophioglossoids and Marattiaceae. In fact, the whisk ferns and Ophioglossoids are demonstrably a clade, and the horsetails and Marattiaceae are arguably another clade. Molecular data—which remain poorly constrained for many parts of the plants' phylogeny — have been supplemented by recent morphological observations supporting the inclusion of Equisetaceae within the ferns, notably relating to the construction of their sperm, and peculiarities of their roots.^[2] However, there are still differences of opinion about the placement of the Equisetum species (see Equisetopsida for further discussion). One possible means of treating this situation is to consider only the leptosporangiate ferns as "true" ferns, while considering the other three groups as "fern allies". In practice, numerous classification schemes have been proposed for ferns and fern allies, and there has been little consensus among them.

A 2006 classification by Smith et al. is based on recent molecular systematic studies, in addition to morphological data. Their phylogeny is a consensus of a number of studies, and is shown below (to the level of orders).^[2][6]

Their classification based on this phylogeny divides extant ferns into four classes:

• Psilotopsida (whisk ferns and ophioglossoid ferns), about 92 species^[7]
• Equisetopsida (horsetails), about 15 species^[7]
• Marattiopsida, about 150 species^[7]
• Polypodiopsida (leptosporangiate ferns), over 9000 species^[7]

The last group includes most plants familiarly known as ferns. Modern research supports older ideas based on morphology that the Osmundaceae diverged early in the evolutionary history of the leptosporangiate ferns; in certain ways this family is intermediate between the eusporangiate ferns and the leptosporangiate ferns. Research by Rai and Graham since this 2006 classification broadly supports the division into four groups, but queries their relationships, concluding that "at present perhaps the best that can be said about all relationships among the major lineages of monilophytes in current studies is that we do not understand them very well".^[8]

Uses[link]

Ferns are not as important economically as seed plants but have considerable importance in some societies. Some ferns are used for food, including the fiddleheads of bracken, Pteridium aquilinum, ostrich fern, Matteuccia struthiopteris, and cinnamon fern, Osmunda cinnamomea. Diplazium esculentum is also used by some tropical peoples as food. Tubers from the King Fern or para (Ptisana salicina) are a traditional food in New Zealand and the South Pacific. Fern tubers were used for food 30,000 years ago in Europe.^[9][10] Fern tubers were used by the Guanches to make gofio in the Canary Islands. Licorice fern rhizomes were chewed by the natives of the Pacific Northwest for their flavor.^{[citation needed]}

Ferns of the genus Azolla are very small, floating plants that do not resemble ferns. Called mosquito fern, they are used as a biological fertilizer in the rice paddies of southeast Asia, taking advantage of their ability to fix nitrogen from the air into compounds that can then be used by other plants.^{[citation needed]}

Many ferns are grown in horticulture as landscape plants, for cut foliage and as houseplants, especially the Boston fern (Nephrolepis exaltata) and other members of the genus Nephrolepis. The Bird's Nest Fern (Asplenium nidus) is also popular, as is the staghorn ferns (genus Platycerium). Perennial (also known as hardy) ferns planted in gardens in the northern hemisphere also have a considerable following.^{[citation needed]}

Several ferns are noxious weeds or invasive species, including Japanese climbing fern (Lygodium japonicum), mosquito fern and sensitive fern (Onoclea sensibilis). Giant water fern (Salvinia molesta) is one of the world's worst aquatic weeds. The important fossil fuel coal consists of the remains of primitive plants, including ferns.^{[citation needed]}

Ferns have been studied and found to be useful in the removal of heavy metals, especially arsenic, from the soil. Other ferns with some economic significance include:^{[citation needed]}

• Dryopteris filix-mas (male fern), used as a vermifuge, and formerly in the US Pharmacopeia; also, this fern accidentally sprouting in a bottle resulted in Nathaniel Bagshaw Ward's 1829 invention of the terrarium or Wardian case
• Rumohra adiantiformis (floral fern), extensively used in the florist trade
• Microsorum pteropus (Java fern), one of the most popular freshwater aquarium plants.
• Osmunda regalis (royal fern) and Osmunda cinnamomea (cinnamon fern), the root fiber being used horticulturally; the fiddleheads of O. cinnamomea are also used as a cooked vegetable
• Matteuccia struthiopteris (ostrich fern), the fiddleheads used as a cooked vegetable in North America
• Pteridium aquilinum or Pteridium esculentum (bracken), the fiddleheads used as a cooked vegetable in Japan and are believed to be responsible for the high rate of stomach cancer in Japan. It is also one of the world's most important agricultural weeds, especially in the British highlands, and often poisons cattle and horses.
• Diplazium esculentum (vegetable fern), a source of food for some native societies
• Pteris vittata (brake fern), used to absorb arsenic from the soil
• Polypodium glycyrrhiza (licorice fern), roots chewed for their pleasant flavor
• Tree ferns, used as building material in some tropical areas
• Cyathea cooperi (Australian tree fern), an important invasive species in Hawaii
• Ceratopteris richardii, a model plant for teaching and research, often called C-fern

Culture[link]

Blätter des Manns Walfarn. by Alois Auer, Vienna: Imperial Printing Office, 1853

Pteridologist[link]

The study of ferns and other pteridophytes is called pteridology. A pteridologist is a specialist in the study of pteridophytes in a broader sense that includes the more distantly related lycophytes.

Pteridomania[link]

"Pteridomania"' is a term for the Victorian era craze of fern collecting and fern motifs in decorative art including pottery, glass, metals, textiles, wood, printed paper, and sculpture "appearing on everything from christening presents to gravestones and memorials." The fashion for growing ferns indoors led to the development of the Wardian case, a glazed cabinet that would exclude air pollutants and maintain the necessary humidity.^[11]

Barnsley fern created using chaos game, through an Iterated function system (IFS).

The dried form of ferns was also used in other arts, being used as a stencil or directly inked for use in a design. The botanical work, The Ferns of Great Britain and Ireland, is a notable example of this type of nature printing. The process, patented by the artist and publisher Henry Bradbury, impressed a specimen on to a soft lead plate. The first publication to demonstrate this was Alois Auer's The Discovery of the Nature Printing-Process.

New Zealand icon[link]

The silver fern in particular has a prominent place within New Zealand culture. Its leaf features as the emblem of many of the country's top national sports teams, including the eponymous Silver Ferns and the All Blacks.

Folklore[link]

Ferns figure in folklore, for example in legends about mythical flowers or seeds.^[12] In Slavic folklore, ferns are believed to bloom once a year, during the Ivan Kupala night. Although alleged to be exceedingly difficult to find, anyone who sees a "fern flower" is thought to be guaranteed to be happy and rich for the rest of their life. Similarly, Finnish tradition holds that one who finds the "seed" of a fern in bloom on Midsummer night will, by possession of it, be guided and be able to travel invisibly to the locations where eternally blazing Will o' the wisps called aarnivalkea mark the spot of hidden treasure. These spots are protected by a spell that prevents anyone but the fern-seed holder from ever knowing their locations.^[13]

Misunderstood names[link]

Several non-fern plants are called "ferns" and are sometimes confused with true ferns. These include:

• "Asparagus fern"—This may apply to one of several species of the monocot genus Asparagus, which are flowering plants.
• "Sweetfern"—A flowering shrub of the genus Comptonia.
• "Air fern"—A group of animals called hydrozoan that are distantly related to jellyfish and corals. They are harvested, dried, dyed green, and then sold as a "plant" that can "live on air". While it may look like a fern, it is merely the skeleton of this colonial animal.
• "Fern bush"—Chamaebatiaria millefolium—a rose family shrub with fern-like leaves.

In addition, the book Where the Red Fern Grows has elicited many questions about the mythical "red fern" named in the book. There is no such known plant, although there has been speculation that the oblique grape-fern, Sceptridium dissectum, could be referred to here, because it is known to appear on disturbed sites and its fronds may redden over the winter. Also, the autumn fern, Dryopteris erythrosora, is well-known for its copper-red color.

Gallery[link]

• 

  Adiantum lunulatum

• 

  Fern leaf, probably Blechnum nudum

• 

  A tree fern unrolling a new frond

• 

  Tree fern, probably Dicksonia antarctica

• 

  Tree ferns, probably Dicksonia antarctica

• 

  "Filicinae" from Ernst Haeckel's Kunstformen der Natur, 1904

• 

  Unidentified tree fern in Oaxaca

• 

  Tree Fern Spores San Diego, CA

• 

  Leaf of fern

• 

  Unidentified fern with spores showing in Rotorua, NZ.

• 

  Ferns in one of many natural Coast Redwood undergrowth settings Santa Cruz, CA.

• 

  Nature prints in The Ferns of Great Britain and Ireland used fronds to produce the plates

• 

  A young, newly-formed fern frond

• 

  Fern fronds

• 

  Fern bed under a forest canopy in woods near Franklin, Virginia

• 

  Pyrrosia piloselloides, Dragon's Scale, in Malaysia

• 

  Fern growing on a wall

• 

  Spores of Dryopteris filix-mas

See also[link]

• British Pteridological Society
• Fern gall
• Fern spike
• Fern sports
• Fiddlehead greens
• Pteridomania

References[link]

• Pryer, Kathleen M., Harald Schneider, Alan R. Smith, Raymond Cranfill, Paul G. Wolf, Jeffrey S. Hunt and Sedonia D. Sipes. 2001. Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants. Nature 409: 618–622 (abstract here).
• Pryer, Kathleen M., Eric Schuettpelz, Paul G. Wolf, Harald Schneider, Alan R. Smith and Raymond Cranfill. 2004. Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. American Journal of Botany 91:1582–1598 (online abstract here).
• Moran, Robbin C. (2004). A Natural History of Ferns. Portland, OR: Timber Press. ISBN 0-88192-667-1.
• Lord, Thomas R. (2006). Ferns and Fern Allies of Pennsylvania. Indiana, PA: Pinelands Press. [1]

External links[link]

Wikispecies has information related to: Pteridophyta

Wikimedia Commons has media related to: Pteridophyta

• Tree of Life Web Project: Filicopsida
• A classification of the ferns and their allies
• A fern book bibliography
• Register of fossil Pteridophyta
• L. Watson and M.J. Dallwitz (2004 onwards). The Ferns (Filicopsida) of the British Isles.
• Ferns and Pteridomania in Victorian Scotland
• Non-seed plant images at bioimages.vanderbilt.edu
• "American Fern Society"
• "British Pteridological Society"
• Checklist of Ferns and Lycophytes of the World

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