|Ferns (Pteridophyta) |
Fossil range: Mid Devonian — Recent
Athyrium filix-femina unrolling young frond
Ferns are vascular plants differing from the more primitive lycophytes by having true leaves (megaphylls). 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 a diploid sporophytic and a haploid gametophytic phase. Unlike the gymnosperms and angiosperms, the ferns' gametophyte is a free-living organism.
Life cycle of a typical fern:
- A sporophyte (diploid) phase produces haploid spores by meiosis;
- A spore grows by mitosis into a gametophyte, which typically consists of a photosynthetic prothallus
- The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis
- A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus
- The fertilized egg is now a diploid zygote and grows by mitosis into a sporophyte (the typical "fern" plant).
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 British 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.
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.
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 trophopylls.
- 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:
- 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
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.
Ferns have traditionally been grouped in the Class Filices, but modern classifications assign them their own division in the plant kingdom, called Pteridophyta.
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 only distantly related to any 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 (Smith et al 2006, and references therein).
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 new classification by Smith et al. (2006) is based on recent molecular systematic studies, in addition to morphological data. This classification divides ferns into four classes:
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.
The complete classification scheme proposed by Smith et al. (2006; alternative names in brackets):
- Class Psilotopsida
- Class Equisetopsida [=Sphenopsida]
- Class Marattiopsida
- Class Pteridopsida [=Filicopsida, Polypodiopsida]
- Order Osmundales
- Family Osmundaceae
- Order Hymenophyllales
- Order Gleicheniales
- Order Schizaeales
- Order Salviniales
- Order Cyatheales
- Order Polypodiales
- Family Lindsaeaceae (incl. Cystodiaceae, Lonchitidaceae)
- Family Saccolomataceae
- Family Dennstaedtiaceae (incl. Hypolepidaceae, Monachosoraceae, Pteridiaceae)
- Family Pteridaceae (incl. Acrostichaceae, Actiniopteridaceae, Adiantaceae, Anopteraceae, Antrophyaceae, Ceratopteridaceae, Cheilanthaceae, Cryptogrammaceae, Hemionitidaceae, Negripteridaceae, Parkeriaceae, Platyzomataceae, Sinopteridaceae, Taenitidaceae, Vittariaceae)
- Family Aspleniaceae
- Family Thelypteridaceae
- Family Woodsiaceae (incl. Athyriaceae, Cystopteridaceae)
- Family Blechnaceae (incl. Stenochlaenaceae)
- Family Onocleaceae
- Family Dryopteridaceae (incl. Aspidiaceae, Bolbitidaceae, Elaphoglossaceae, Hypodematiaceae, Peranemataceae)
- Family Oleandraceae
- Family Davalliaceae
- Family Polypodiaceae (incl. Drynariaceae, Grammitidaceae, Gymnogrammitidaceae, Loxogrammaceae, Platyceriaceae, Pleurisoriopsidaceae)
- Order Osmundales
Ferns are not as important economically as seed plants but have considerable importance. 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.
Ferns of the genus Azolla are very small, floating plants that do not look like 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.
A great many ferns are grown in horticulture as landscape plants, for cut foliage and as houseplants, especially the Boston fern (Nephrolepis exaltata). The Bird's Nest Fern, Asplenium nidus, is also popular, and the staghorn ferns, genus Platycerium, have a considerable following.
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.
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:
- 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 adiantoides (floral fern), extensively used in the florist trade
- 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 (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
In Slavic folklore, ferns are believed to bloom once a year, during the Ivan Kupala night. Although it's exceedingly difficult to find, anyone who takes a look of a fern flower will be happy and rich for the rest of his life. Similarly in Finland, the tradition holds that one who finds the seed of a fern in bloom on Midsummer night, will by the possession of it be able to travel under a glamour of invisibility and shall be guided to the locations where eternally blazing Will o' the wisps mark the spot of hidden treasure caches.
"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. 
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.
Ferns are sometimes used in medicine to treat cuts and clean them out. Ferns are also good bandages if you are stuck out in the wild. Rubbing a sword fern frond spore-side-down on a stinging nettle sting removes the stinging. 
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.
Unidentified tree fern in Oaxaca
Tree Fern Spores San Diego, CA
This article is about the group of pteridophyte plants. For the environmental organisation, see FERN. For the letter of the Ogham alphabet, see Fern (letter). For other uses, see Fern .
(Tumbuhan Paku Tanduk Rusa)
Platycerium bifurcatum, the Elkhorn fern, occurs naturally in New Guinea, and along the coasts of Queensland and New South Wales. It is cultivated in many countries, it has become naturalised (that is, it has spread into the wild) in Florida, and it has been listed as an environmentally invasive species in Hawaii. It belongs in the family Polypodiaceae, which has 10 genera and 26 species in Australia.
The Elkhorn fern is an epiphyte, growing on the trunks and branches of trees. Each plant is composed of a mass of plantlets. A plantlet consists of a nest leaf 12-30 cm wide, lying against the bark of the host tree. The nest leaves of neighbouring plantlets overlap one another. The nest leaves become brown and papery with age, and do not produce spores (they are sterile). Fertile fronds 25-90 cm long protrude from each plantlet. Each frond divides into two segments a number of times along its length. Spores are produced on the undersurface of the end segments of each frond. The spore producing areas are coloured tan brown, and have the texture of velvet cloth.
The easiest way to propagate P. bifurcatum is to remove a plantlet and then tie it to the desired new location. A large old knife, or a thin flat trowel, may be used to remove a plantlet from the rest of the plant. The implement should be inserted beneath the membrane of a plantlet and then used to prize the roots of the plantlet from the other plantlets. The plantlet may then be tied to its new location with lengths of cloth or stocking. If the new plant is required to be of a large size, then a number of plantlets can be removed together from a large P. bifurcatum plant.
Platycerium bifurcatum may also be propagated from its spores. To collect the spores, place the part of a frond that is producing spores in a brown paper bag. Leave the frond in the bag until there is brown dust in the bag, which are the spores. Fill a plastic or terracotta pot with peat moss, and pour boiling water through the peat moss to sterilize it. Immediately place a glass or plastic sheet over the pot to keep it sterile. Once the peat moss has cooled down, spread the spores evenly over the surface of the peat moss, then immediately replace the glass or plastic sheet over the pot. Stand the bottom of the pot in an ice cream container with a shallow layer of water, and place the pot and container in a warm position receiving indirect sunlight. Once the spores have germinated, a green scum will initially appear over the surface of the peat moss. After a period of weeks to months, the fronds of the Elkhorn fern will begin to appear and the glass cover of the pot can be removed. Once the new plants have grown larger, they can be transferred to a tree trunk.
P. bifurcatum plants require a shady area to grow in, and need to be kept moist. They are not prone to attack from many pests and insects, but may be preyed upon by scale bugs and mealy bugs. These pests may be removed from the plant by scratching them off. Ladybirds will eat these pests, and so may help to control them.
Derivation of the name:
Platycerium - is derived from the Greek words platys meaning "flat" and ceras meaning "a horn", referring to the shape of the fronds.
bifurcatum - means to fork into two branches, again, referring to the shape of the fronds.
Text by Robert Mason (2004 Student Botanical Intern