"Pteridophytes (Ferns)". In: Encyclopedia of Life Sciences

Pteridophytes (Ferns) 

George Yatskievych, Missouri Botanical Garden, St Louis, MO, USA 

Pteridophytes (vascular cryptogams or ferns and fern allies) comprise about 12 000 species 

of primitive vascular plants; they do not produce flowers or seeds and reproduce instead via 

spores. They occur in most terrestrial habitats and also in some aquatic communities. Some 

species are very beneficial to humans, but the group also contains important species of 

weeds. 

Introduction 

Pteridophytes, also known as ‘vascular cryptogams’ and 

‘ferns and fern allies’, comprise about 12 000 species of 

vascular plants that do not produce flowers or seeds, 

reproducing instead via the production of spores. Pteridophytes 

occur in most terrestrial habitats on earth and 

are also present in some aquatic communities. They are an 

important part of the ground vegetation in many forest 

communities and, with about one-third of the species 

growing on the trunks and branches of trees, they are also 

an important component of many epiphytic plant communities. 

Some species are very beneficial to humans, but 

the group also contains some of the most important weed 

species in the world. 

Life Cycle 

Pteridophytes are characterized by a life cycle that usually 

involves an alternation of two free-living generations – 

sporophyte and gametophyte – with the sporophyte the 

larger phase of the life cycle. Nonvascular plants like 

mosses and liverworts also have an alternation of generations, 

but in these organisms the gametophyte generation is 

generally the dominant phase. In seed plants, the 

gametophyte is no longer free-living but remains enclosed 

in tissues on the sporophyte and there is a progressive 

reduction in the size through various gymnosperm groups 

such that in flowering plants (angiosperms) the gametophyte 

generation is reduced to just a few cells in the 

germinating pollen grains and the ovules. 

The conspicuous phase of the pteridophyte cycle is the 

sporophyte, which is how most people observe the plants in 

nature. These are usually perennial. Sporangia are 

produced on the leaves of sporophytes (sometimes in 

specialized cone-like strobili). In true ferns, these are 

commonly on the leaf undersurface and are often clustered 

into discrete units called sori. Within each sporangium, 

specialized cells undergo a series of mitotic (structural) 

divisions followed by meiosis (sexual division) that results 

in production of spores with half as many chromosomes as 

in the original sporophyte. The more advanced ferns 

. Introduction 

. Life Cycle 

Introductory article 

. Reproductive Variations 

. Cytology 

Article Contents 

. Morphology and Anatomy 

. Systematics and Classification 

. Economic Importance 

usually have 64 spores per sporangium, but more primitive 

ferns and fern allies may have hundreds or even thousands. 

At maturity, the sporangium dries and ruptures, dispersing 

the spores into the air. 

When a spore lands on a suitable substrate, it 

germinates, the cells dividing and forming first a filament 

and eventually usually a heart-shaped gametophyte (sometimes 

other shapes in some groups) that is the same species 

as the sporophyte but appears very different. Gametophytes 

are often moss-like in appearance and are quite 

small, usually less than 1 cm wide at maturity, but are often 

fairly easily located in nature near adjacent sporophytes. 

Although in a few genera gametophytes can be long-lived, 

in most ferns their lifespan is usually much less than a year. 

They are the sexual phase of the life cycle in that they 

produce multicellular sex organs at maturity on the side 

away from the light. The more or less spherical antheridia 

(male gametangia) are produced among the rhizoids 

towards the base of the plant and at maturity they pop 

open to release motile flagellated spermatozoids. Archegonia 

(female gametangia) are usually produced at the 

opposite end near the notch region, and are flask-shaped 

structures containing a single egg cell. A film or droplet of 

free-standing water is necessary in order for the spermatozoids 

to swim to an archegonium of the same or a 

different gametophyte. The neck cells of the archegonium 

spread at maturity and the spermatozoid swims down the 

archegonial canal to fuse with the egg, effecting syngamy 

(fertilization) and forming a zygote with twice the number 

of chromosomes as the gametophyte. This zygote grows 

and develops into a new sporophyte, completing the cycle, 

while the maternal gametophyte withers away. 

In a typical pteridophyte, each gametophyte is potentially 

bisexual, producing both antheridia and archegonia. 

Because the eggs and spermatozoids of an individual all 

grew from a single spore and are thus genetically identical, 

potentially these plants can become self-fertilized in a way 

that renders the resultant sporophyte entirely homozygous 

(having only one kind of allele for each gene locus) for its 

entire makeup. Various mechanisms exist to promote 

cross-fertilization: the gametangia often mature at different 

times; the genome may have deleterious alleles that are 

ENCYCLOPEDIA OF LIFE SCIENCES © 2002, John Wiley & Sons, Ltd. www.els.net 

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fatal to homozygous individuals (genetic load); and there 

may exist mating factors that prevent successful selffertilization. 

Some ferns also produce pheromones known 

as antheridiogens, in which the first spore to germinate at a 

site becomes a female gametophyte and exudes a substance 

causing later-germinating spores to develop into male 

gametophytes. 

Reproductive Variations 

Unusual gametophytes 

In some ferns and fern allies, including some clubmosses 

(Lycopodiaceae), whisk ferns (Psilotaceae), and grape 

ferns (Ophioglossaceae), the gametophytes are not surfacedwelling 

and green. Instead, they are subterranean and 

nonphotosynthetic, often appearing as pale brown or 

yellow fuzzy cylinders or pads of tissue. These gametophytes 

are mycotrophic; that is, they receive their nutrients 

from soil-borne fungi that establish connections with their 

rhizoids. However, although such gametophytes are 

usually slow-growing, they usually produce normal 

gametangia and otherwise complete their life cycles in the 

typical fashion. 

Heterospory 

Other ferns and fern allies, including spike mosses 

(Selaginellaceae), quillworts (Isoetaceae), and aquatic 

ferns (Azollaceae, Marsileaceae, Salviniaceae), depart 

from the typical life cycle in producing two different types 

of sporangia. One of these produces numerous microscopic 

microspores that germinate to produce male gametophytes. 

The other sporangial type produces many fewer 

and much larger megaspores (usually visible to the naked 

eye), which grow into female gametophytes. In both spore 

types the gametophytes are reduced in structure and 

develop mostly within the ruptured spore wall. 

Vegetative reproduction 

Many pteridophytes supplement their sexual cycles with 

various forms of vegetative reproduction. This may be as 

simple as the fragmentation of a creeping rhizome into 

smaller pieces that become established as separate plants. 

Horsetails (Equisetaceae) growing along rivers and 

streams are frequently spread over long distances in this 

fashion by flooding. Other species develop specialized 

structures to effect vegetative propagation. Some ferns 

produce stolons, which are specialized long, spreading 

stems that root at their tips and form new plants. Others 

produce buds or bulbils on their leaves that can germinate 

to form new plantlets. Still others produce roots where 

their fronds come into contact with soil. A few species 

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produce specialized underground structures, such as tubers 

and similar offsets. Some species have sporophytes or 

gametophytes that produce gemmae, which are specialized 

relatively undeveloped fragments of plants that break off 

and are dispersed, eventually germinating to form new 

plants. In a few species of filmy ferns (Hymenophyllaceae), 

shoestring ferns (Vittariaceae), and other families, the 

ability to produce sporophytes has been lost and the plants 

exist only as colonies of gametophytes spreading through 

the production of tiny air-dispersed gemmae. 

Apogamy 

Apogamy is a widespread and important mechanism of 

reproduction in pteridophytes more than in any other 

group of plants. Apogamous ferns, which frequently occur 

in environments with seasonal extremes of heat, cold and/ 

or drought, avoid the necessity for sex. In the sporangia of 

such plants, a mechanism during the series of cell divisions 

results in the production of spores with the same genetic 

constitution as the sporophyte plant (meiosis does not 

result in a reduction in chromosomal ploidy). These 

‘diplospores’ grow into gametophytes that produce new 

sporophytes directly from meristematic tissues near the 

notch region. The environmental advantages of apogamy 

include the faster development of the gametophyte and the 

release from the requirement of standing water for 

fertilization to take place. Interestingly, many apogamous 

ferns continue to produce antheridia with functional 

spermatozoids, which can be released and fertilize eggs 

on nearby gametophytes of related sexual species. Once 

formed, such hybrids are always apogamous and thus able 

to reproduce themselves. 

Cytology 

Pteridophytes characteristically have high chromosome 

numbers. The highest chromosome number recorded for 

any organism is in an adder’s tongue fern, Ophioglossum 

reticulatum, with about 1260 pairs of chromosomes. The 

base chromosome number (x) in various genera is quite 

variable: for example, Asplenium (x 5 36), Botrychium 

(x 5 45), Osmunda (x 5 22), Pellaea (x 5 29), Polystichum 

(x 5 41); and Pteridium (x 5 52). Exceptions occur in a few 

ferns, including most aquatic genera (Salvinia, x5 9). 

Some fern allies also have low chromosomal base numbers 

(Selaginella, x5 mostly 7–10). 

Several theories have been advanced as to why ferns have 

so many chromosomes. Among the most intriguing is that 

of palaeopolyploidy. Botanists have long known that 

polyploidy (the development of extra sets of chromosomes 

over the basic diploid level) is very widespread and 

common in pteridophytes. Both autopolyploidy and 

allopolyploidy have been documented in numerous genera.

Allopolyploidy involves hybridization between species, 

resulting in a sterile hybrid that regains its fertility by 

doubling its chromosome number during spore production 

in some sporangia. Autopolyploidy involves the same 

doubling of chromosome number during spore production 

but without a hybridization event. With polyploidy so 

pervasive among pteridophytes, geneticists have long been 

puzzled that most fern species are apparently functionally 

diploid, having only two alleles for each gene locus. In the 

last two decades, ‘gene-silencing’ – the selective shutting off 

of duplicate copies of genes found in polyploid species – 

has been documented in several fern genera. This has given 

rise to the hypothesis that, over time, ferns undergo regular 

rounds of polyploidy (which increases their chromosome 

numbers) followed by gradual diploidization of the 

genomes (selective silencing of the extra gene copies to 

return the species to a functionally diploid level). Evidence 

for this mechanism is circumstantial, but it seems likely to 

function in at least those cases that have been better studied 

thus far. 

Morphology and Anatomy 

Sporophytes 

Stems 

Most ferns have specialized stems called rhizomes that are 

positioned at the level of the substrate or somewhat buried. 

Rhizomes vary greatly in size, thickness and orientation. 

Most commonly, they are horizontal and creeping, but 

many species have short upright rhizomes. In some groups, 

notably the tree ferns, specialized stems are trunk-like and 

may be 20 m or more tall. These modified stems produce 

only adventitious roots and are usually covered with dense 

scales or hairs, at least towards the growing tip. 

Other types of stems occur in some primitive ferns and in 

most fern allies. Grape ferns (Ophioglossaceae) usually 

have somewhat tuberous stems. Horsetails (Equisetaceae) 

have both rhizomes and fluted or ridged aerial stems. 

Quillworts (Isoetaceae) have very short stout stems with 

the nodes very close together (corms). Most clubmosses 

(Lycopodiaceae) have relatively unspecialized stems 

Rhizomes are structurally simpler than those of most 

seed plants in that they do not produce secondary growth 

(wood). Even the tree ferns have only primary growth, and 

a thick mantle of interwoven roots is produced to help with 

structural support. In most ferns, the vascular system of the 

stem is in the form of a hollow cylinder interrupted (with 

gaps) where traces branch off to the leaves. In crosssection, 

most fern rhizomes thus appear as an irregular ring 

of vascular bundles. In some primitive ferns and fern allies, 

the vascular system is a solid uninterrupted cylinder. 


Leaves 

Pteridophytes exhibit an amazing variety of leaf morphologies. 

In most fern allies and a few primitive ferns, the 

leaves are reduced and scale-like, needle-like or grass-like, 

with at most a single vein. In most true ferns, however, the 

leaves are the dominant organ of the sporophyte and can be 

extremely complex in their pattern of division. In a few 

genera (especially in the Gleicheniaceae), the leaves are 

indeterminate in growth; that is, they continue to elongate 

at the tip, often reaching several metres in length and 

clambering over surrounding vegetation. The petiole 

(stipe) of fern leaves may be circular, angled, or U-shaped 

in cross-section, and is sometimes hairy or scaly. There are 

one to several vascular strands, and the number and 

position of these in the petiole are often diagnostic for 

individual families or genera. 

In most ferns, the development of the leaf follows a 

pattern known as ‘circinate vernation’. This produces a 

characteristic fiddlehead or crozier as the leaf uncurls. In a 

few genera, this pattern has become modified so that the 

unfurling leaf produces a hook-like structure. The fern 

allies and the grape ferns (Ophioglossaceae) do not exhibit 

circinate vernation but expand by unfolding or in an 

indefinite pattern. 

The leaf blade (lamina) varies from entire to highly 

divided, with pinnate, pedate and palmate patterns of 

division in various species, but most commonly is one or 

more times pinnately compound. The continuation of the 

petiole as the central axis of the leaf blade is known as the 

rachis, to which the pinnae (primary divisions or leaflets) 

are attached. The pinnae may themselves be entire or one 

or more times compound. The ultimate divisions of the leaf 

are called pinnules, which may be entire or lobed. Venation 

of the leaves can be quite complex, with several orders of 

successively finer midveins (costae) and lateral veins. The 

venation of the pinnules may be unbranched or branched 

with free to variously anastomosing veinlets. 

Fern leaves may be glabrous or variously covered with 

hairs and/or scales. In some species, the leaves are 

glandular and sticky. Other species secrete a powdery 

farina, usually on the leaf undersurface, which may be 

white or bright yellow or orange. The leaves also vary 

greatly in thickness and texture. The thinnest leaves occur 

in the filmy ferns (Hymenophyllaceae), in which the leaves 

are often only two cell layers thick. The production of 

thick, leathery leaves or leaves with dense vestiture of hairs, 

scales, glands or farina is generally explained as adaptation 

to droughty habitats and/or areas of high sunlight. 

Sporangia 

In fern allies and a few primitive ferns, relatively large 

sporangia are produced either in complex cone-like strobili 

at the stem or branch tips or in the axils at the bases of 

leaves. Some fern species produce dimorphic leaves, with 

vegetative (trophophyll) and fertile (sporophyll) leaves 

3

having different morphologies. In other ferns, the leaf is 

divided into specialized fertile and vegetative regions. 

However, in most ferns, the sporangia are produced on the 

undersurface of normal leaves. 

The positional patterns and other details of sporangia on 

the leaf undersurface are often diagnostic for particular 

families or genera and are a principal tool in fern 

classification. At one extreme, the sporangia may entirely 

cover the leaf undersurface (acrostichoid). In contrast, in 

some primitive ferns, the sporangia are sparsely scattered 

along some veins. In most ferns, however, the sporangia 

are grouped into discrete lines or clusters known as sori. 

Sori may be circular to linear, positioned along the margin 

or towards the midvein (costa), surficial or in a groove or 

channel, etc. In some cases, the developing sori are 

protected by a recurved leaf margin (false indusium), a 

covering of deciduous scales, or a more permanent small 

flap of tissue, the indusium. Indusia vary greatly in shape, 

size, texture and persistence, ranging from umbrellashaped 

to globose to linear. In the water ferns (Azollaceae, 

Marsileaceae, Salviniaceae), the sporangia become enclosed 

in hardened capsular structures called sporocarps 

that are formed either from modified leaflets or from 

modified indusia. 

The sporangia themselves are usually positioned on a 

somewhat thickened vein ending or along a portion of a 

vein. In most cases, the sporangium consists of a stalk, of 

varying length and cell number, and a multicellular 

capsule. In most ferns, the capsule is differentiated into 

thin-walled cells and an annulus, a ring or region of cells 

with only some of the walls thickened. The annulus 

functions in spore release. 

Spores 

Spores are the main structures by which ferns are dispersed 

to form new populations. As such, in most ferns, they are 

relatively impervious, long-lived and metabolically inactive. 

Although the majority of spores produced fall within a 

few metres of the parental sporophyte, the spores of some 

ferns have been recovered from air currents in the 

stratosphere during high-elevation atmospheric sampling 

studies and ferns are among the most successful colonists 

of highly isolated oceanic islands. Although the life of most 

spores is measured in terms of months or a few years, in 

some cases fern spores have been induced to germinate 

after more than a hundred years of storage. In a few groups 

scattered throughout the ferns and fern allies, the spores 

are relatively thin-walled, green and photosynthetically 

active, and relatively short-lived, reflecting an adaptation 

to rapid establishment of new plants following dispersal. 

Developmentally, spores are the direct products of 

meiosis, which begins with a single spore mother cell 

undergoing two separate rounds of division, and yields a 

tetrad of products that breaks apart into four individual 

4 


spores. The spatial relationship between the plane of 

division of the two rounds of meiotic division affects the 

shape and markings of the resulting spores. Two main 

types are recognized. Trilete (tetrahedral) spores vary from 

nearly spherical to somewhat three-angled and have a 

three-branched scar where each spore was attached to the 

others in the tetrad. Monolete (bilateral) spores are 

ellipsoid to bean-shaped and have a linear attachment 

scar along one side. The attachment scar is usually where 

the spore ruptures during germination. As it matures, each 

spore develops two or three outer protective layers, the 

relatively thin endospore, the thick perispore, and in some 

cases an outermost exospore. The exospore and also 

portions of the perispore actually develop from materials 

produced by the inner sporangium wall and deposited over 

the spore, rather than by the spore itself. 

Mature spores vary greatly in size and surface sculpturing. 

Spores of some Marattiaceae are only about 15 mmin 

diameter, whereas the megaspores of some Selaginella 

species may approach 1 mm. The surface sculpturing is 

often diagnostic for various species, genera and/or 

families, ranging from smooth to wrinkled, spiny and/or 

with wing-like ridges. 

Gametophytes 

Upon germination of spores, cell divisions produce first a 

filamentous structure. In most ferns, this subsequently 

continues to divide in two or more planes and eventually 

differentiates into the mature gametophyte. The typical 

fern gametophyte is a flat, heart-shaped structure, with two 

lobes and an intervening notch at one end and the other end 

narrowed or rounded. It can vary in size from a few 

millimetres to about 1 cm in size. A number of variations 

exist but are not widespread, including filamentous, strapshaped 

and irregularly lobed gametophytes. In pteridophytes 

with subterranean mycorrhizal gametophytes, these 

can mature to various shapes, but most are either tubular 

or cushion-shaped. 

Gametophytes are moss-like in that they lack vascular 

tissue and roots. Slender hair-like structures called rhizoids 

function to absorb water and nutrients and act to anchor 

the gametophyte to the substrate. The gametangia (sex 

organs) generally are formed on the side of the gametophyte 

away from the light (except in subterranean 

gametophytes). The antheridia are positioned among the 

rhizoids and are more or less spherical structures consisting 

of a jacket of cells enclosing the spermatozoids. The 

archegonia are usually positioned near the notch on a 

slightly thickened pad of tissue. They are flask-shaped and 

somewhat sunken into the tissue. The neck of the 

archegonium consists of four columns of cells that separate 

at maturity, opening a canal and exposing the egg cell in the 

base for fertilization by the spermatozoid.

Systematics and Classification 

Classification of pteridophytes remains somewhat controversial. 

The terms ‘pteridophytes’, ‘ferns and fern allies’ 

and ‘vascular cryptogams’ continue to be used informally 

by botanists who wish to avoid becoming enmeshed in the 

technical details of competing systems of fern classification. 

Although many of the groups of ferns and fern allies 

are distinctive and have been recognized since antiquity, 

the relationships among these groups and the taxonomic 

level at which they should be recognized still has not been 

fully resolved. In recent years, a consensus has begun to 

emerge, and molecular phylogenetic studies involving 

mostly the comparison of various gene sequences have 

helped to refine theories of pteridophyte evolution and 

taxonomy. 

In general, pteridophytes have a long fossil record and 

the main lineages trace their origins to the first vascular 

land plants. Pteridophytes were dominant plants in the 

swamps of the Carboniferous Period more than 300 million 

years ago, which gave rise to the world’s major coal 

deposits. In some groups, such as the horsetails (Equisetaceae), 

the relatively few modern species are the remnants 

of formerly much more diverse lineages. On the other hand, 

some modern fern species have existed for long times, as 

shown by the fossils indistinguishable from the modern 

sensitive fern (Onoclea sensibilis) dating back to the 

Palaeocene Epoch more than 60 million years ago. 

In recent years, a fundamental shift in our understanding 

of primitive pteridophyte classification has 

occurred. Traditionally, three or four main groups had 

been recognized. These included the clubmosses and 

related groups (lycophytes), the horsetails (sphenophytes, 

sometimes called arthrophytes), the true ferns (filicaleans), 

and sometimes the whisk ferns (psilophytes). The psilophytes, 

an unusual group with structurally relatively 

simple plants, were considered the most primitive group 

of extant vascular plants by some botanists and true ferns 

with reduced simplified structure by others. Recent 

anatomical and molecular studies have shown that the 

latter interpretation is probably correct – the Psilotaceae 

are primitive ferns whose stems, leaves and sporangia have 

become simplified over time. These same studies have 

yielded an even more fundamental conclusion. The 

lycophytes are apparently the most primitive group of 

extant vascular plants. The lineage leading to the seed 

plants (gymnosperms and angiosperms) has its origins 

within the pteridophyte lineage before the divergence of 

both the true ferns and the horsetails. Thus, the most recent 

hypothesis of pteridophyte evolution advocates the existence 

of two fundamental groups, the lycophytes and the 

remaining ferns and fern allies. 

There are a number of relatively primitive fern families, 

many of which are represented by relatively few modern 

species but some of which have extremely long fossil 

records. The greatest diversity of modern species exists 

among the most advanced fern groups, and the number of 

families to be accepted and the relationships among these 

families are the topic of intensive systematic research at 

present. 

Table 1 summarizes current hypotheses concerning 

pteridophyte classification, from most primitive to most 

advanced. An estimate of the number of extant genera and 

species, in parentheses, follows each family name, and also 

the common names of selected well-known examples. 

Economic Importance 


Relatively few species of pteridophytes are economically 

important. Perhaps the best-known current use is horticultural, 

as garden plants, house plants and specimen 

plants in conservatories and greenhouses. One species, 

Ruhmora adiantiformis is often called florist’s fern; its finely 

divided but thick and leathery leaves resist wilting and are 

used in cut flower arrangements. Another horticultural 

practice has been the use of chunks of the dense rotresistant 

root mantles covering the stems of tree ferns 

(known as orchid bark) as a substrate for growing orchids 

and other plants that are epiphytic in nature. However, this 

has caused the decline and endangerment of numerous tree 

fern species, with the result that commercial trade in tree 

fern products is now strictly regulated by international law 

and trade treaties. 

A number of ferns have been used in handicrafts. 

Petioles of some members of the climbing fern family, 

Schizaeaceae, as well as other groups, are used in some 

tropical countries for colour designs in basketry and 

bracelets. Pteridium (bracken) leaves have been used to 

make a green dye. The rhizomes of the tree fern Cibotium, 

which are covered with dense, long, golden hairs, have been 

fashioned since antiquity into animal statue curios sometimes 

known as ‘vegetable lamb of Tartary’. 

One group of pteridophytes with an extensive history of 

use is the clubmosses (Lycopodiaceae). The microscopic 

spores of these fern allies contain nonvolatile oils that 

made them useful as dry industrial lubricants. They have 

also been used to keep latex items such as surgical gloves 

and condoms from sticking together, but this practice has 

been mostly discontinued since it was discovered that the 

spores caused skin irritation and allergic reactions in some 

people. Other uses of the spores have been in flash powder 

for photography and in fingerprint powder used in forensic 

investigation. 

Various ferns are also eaten as food, with the young 

foliage usually steamed as a vegetable or dried and used as 

an additive in stews and sauces. Several species are eaten, 

including Diplazium esculentum (which is cultivated for this 

purpose in parts of Asia), but the commercially most 

important species in the western hemisphere is Matteuccia 

struthiopteris, the ostrich fern, whose fiddleheads are a 

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Table 1 Summary of the classification of extant pteridophyte families 

Lycophytes (Division Lycopodiophyta) (4 extinct orders 1 3 extant orders (each with 1 family)) 

Lycopodiaceae (4/380), clubmosses 

Isoetaceae (1/130), quillworts 

Selaginellaceae (1/800), spikemosses 

Ferns (Division Pteridophyta) 

Eusporangiate ferns (3 extant orders, each with 1 family) 

Psilotaceae (2/12), whisk ferns 

Ophioglossaceae (3–8/80), grape ferns 

Marattiaceae (4/100), giant ferns 

Sphenophytes (3 extinct orders 1 Equisetales) 

Equisetaceae (1/15), horsetails 

Leptosporangiate ferns (1 extinct order 1 about 10 extant orders) 

Primitive isolated groups (6 orders (each with 1 modern family except that Cheiropleuriaceae is in Dipteridales)) 

Osmundaceae (3/20), cinnamon and royal ferns 

Hymenophyllaceae (2 or 3/650), filmy ferns 

Stromatopteridaceae (1/1) 

Gleicheniaceae (4/150), scrambling ferns 

Cheiropleuriaceae (1/1) 

Dipteridaceae (1/8) 

Schizaeaceae (5/200), climbing ferns, curly grass fern 

Heterosporous aquatic groups (Order Marsileales, also called Hydropteridales) 

Marsileaceae (3/70), water clovers 

Azollaceae (1/6), mosquito ferns 

Salviniaceae (1/11), water spangles 

Tree ferns (Order Cyatheales) 

Loxomataceae (2/2) 

Plagiogyriaceae (1/11) 

Matoniaceae (2/4) 

Metaxyaceae (1/2) 

Dicksoniaceae (5/28–33), tree ferns 

Lophosoriaceae (1/1) 

Hymenophyllopsidaceae (1/8) 

Cyatheaceae (14–20/620–675), tree ferns 

Advanced groups (Order Polypodiales) 

Lindsaeaceae (5/200) 

Dennstaedtiaceae (14/350), cup ferns, hay-scented fern, bracken 

Pteridaceae (35–45/1150), cliff brakes, lip ferns, goldback ferns, maidenhair ferns, shoestring ferns 

Aspleniaceae (1/800), spleenworts 

Thelypteridaceae (1–35/900) 

Blechnaceae (8/250), chain ferns 

Dryopteridaceae (including Tectariaceae) (30/950), wood ferns, shield ferns, halberd ferns, ostrich fern, sensitive fern 

Woodsiaceae (including Athyriaceae) (10–13/500), fragile ferns, lady ferns, oak ferns 

Lomariopsidaceae (6/550), paddle ferns, tongue ferns 

Davalliaceae (14/120), rabbit’s foot ferns, Boston fern 

Polypodiaceae (including Grammitidaceae) (35–45/1050), polypodies, staghorn ferns 

common sight in markets of the northeastern United States 

in late spring. Formerly, Pteridium aquilinum (bracken) 

was quite important in some cuisines, particularly in parts 

of eastern Asia. However, medical studies have linked this 

species to stomach cancer and its use has declined. 

6 


Perhaps the most economically valuable species of 

pteridophyte is Azolla, a genus of tiny floating aquatic 

ferns. For centuries farmers in parts of eastern Asia 

jealously guarded strains of this plant, which they used to 

inoculate rice paddies in the spring for markedly increased 

yields. During the Vietnam War era, this practice came to

the attention of western scientists. They ‘discovered’ that 

hollow chambers in Azolla leaves contain symbiotic 

cyanobacteria (Anabaena azollae) that are able to convert 

atmospheric nitrogen into the nitrate form that serves as a 

major plant nutrient. Thus, the fast-growing plants of 

Azolla acted as a living source of fertilizers. During the past 

few decades, millions of dollars have been spent to locate 

superior strains of this fern and to make the process more 

efficient, in an attempt to increase rice production in 

developing countries. 

A few ferns have had negative economic impacts because 

of their weediness. Two of the best examples include 

Salvinia and Pteridium. Salvinia molesta (Kariba weed, 

giant salvinia) is a floating aquatic fern that is weedy 

throughout the warmer parts of the world. In some 

situations it can form a mat several inches thick on the 

surface, that prevents light and oxygen penetrating into the 

water. In places such as New Guinea, this fern has at times 

threatened to destroy local fishing economies, and it is 

being carefully eradicated where found outside of its 

natural range in southern Brazil. Pteridium aquilinum 

(bracken) is a coarse fern with an immense creeping 

rhizome capable of reaching lengths of 400 m. The plant 

quickly invades open habitats, competing vigorously with 

other plants. Because the plants are toxic to livestock, 

bracken has ruined the pasturage on large acreages of land, 

especially in parts of Europe. 

Further Reading 


Camus JM, Gibby M and Johns RJ (eds) (1996) Pteridology in 

Perspective. Kew, UK: Royal Botanic Gardens. 

Galston AW (1975) The water fern–rice connection. Natural History 

84(12): 10–11. 

Hoshizaki BJ and Moran RC (2001) Fern Grower’s Manual, revised edn. 

Portland, OR: Timber Press. 

Kramer KU and Green PS (eds) (1990) Pteridophytes and Gymnosperms; 

vol. 1 in Kubitzki K (ed.) The Families and Genera of Vascular Plants. 

Berlin: Springer-Verlag. 

May LW (1979) The economic uses and associated folklore of ferns and 

fern allies. Botanical Review (Lancaster) 44: 491–528. 

Perring FH and Gardiner BG (eds) (1976) The biology of bracken. 

Botanical Journal of the Linnaean Society 73: 1–302. 

Pryer KM, Schneider H, Smith AR et al. (2001) Horsetails and ferns are a 

monophyletic group and the closest living relatives to seed plants. 

Nature 409: 618–622. 

Sheffield E, Wolf PG and Haufler CH (1989) How big is a bracken plant? 

Weed Research 29: 455–460. 

Tryon RM and Tryon AF (1982) Fern and Allied Plants, with Special 

Reference to Tropical America. New York: Springer-Verlag. 

Wolf PG (ed.) (1995) Use of molecular data in evolutionary studies of 

pteridophytes. American Fern Journal 85: 101–428. 

Wolf PG, Sipes SD, White MR et al. (1999) Phylogenetic relationships of 

the enigmatic fern families Hymenophyllopsidaceae and Lophosoriaceae: 

evidence from rbcL nucleotide sequences. Plant Systematics 

and Evolution 219: 263–270. 

7

"Pteridophytes (Ferns)". In: Encyclopedia of Life Sciences

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