A pteridophyte is a vascular plant (with xylem and phloem) that reproduces using spores. Because pteridophytes produce neither flowers nor seeds, they are also referred to as "cryptogams", meaning that their means of reproduction is hidden. The pteridophytes include the ferns, horsetails, and the lycophytes (clubmosses, spikemosses, and quillworts). These are not a monophyletic group because ferns and horsetails are more closely related to seed plants than to the lycophytes. Therefore, "Pteridophyta" is no longer a widely accepted taxon, although the term pteridophyte remains in common parlance, as do pteridology and pteridologist as a science and its practitioner, to indicate lycophytes and ferns as an informal grouping, such as the International Association of Pteridologists and the Pteridophyte Phylogeny Group.
Informal paraphyletic group of vascular plants that reproduce by spores
Ferns and lycophytes (pteridophytes) are free-sporing vascular plants that have a life cycle with free-living, independent gametophyte and sporophyte phases. Their other common characteristics include vascular plant apomorphies (e.g., vascular tissue) and land plant plesiomorphies (e.g., spore dispersal and the absence of seeds). 
Of the pteridophytes, ferns account for nearly 90% of the extant diversity. Smith et al. (2006), the first higher-level pteridophyte classification published in the molecular phylogenetic era, considered the ferns as monilophytes, as follows:
where the monilophytes comprise about 9,000 species, including horsetails (Equisetaceae), whisk ferns (Psilotaceae), and all eusporangiate and all leptosporangiate ferns. Historically both lycophytes and monilophytes were grouped together as pteridophytes (ferns and fern allies) on the basis of being spore-bearing ("seed-free"). In Smith's molecular phylogenetic study the ferns are characterised by lateral root origin in the endodermis, usually mesarch protoxylem in shoots, a pseudoendospore, plasmodial tapetum, and sperm cells with 30-1000 flagella. The term "moniliform" as in Moniliformopses and monilophytes means "bead-shaped" and was introduced by Kenrick and Crane (1997) as a scientific replacement for "fern" (including Equisetaceae) and became established by Pryer et al. (2004). Christenhusz and Chase (2014) in their review of classification schemes provide a critique of this usage, which they discouraged as irrational. In fact the alternative name Filicopsida was already in use. By comparison "lycopod" or lycophyte (club moss) means wolf-plant. The term "fern ally" included under Pteridophyta generally refers to vascular spore-bearing plants that are not ferns, including lycopods, horsetails, whisk ferns and water ferns (Marsileaceae, Salviniaceae and Ceratopteris), and even a much wider range of taxa. This is not a natural grouping but rather a convenient term for non-fern, and is also discouraged, as is eusporangiate for non-leptosporangiate ferns.
However both Infradivision and Moniliformopses are also invalid names under the International Code of Botanical Nomenclature. Ferns, despite forming a monophyletic clade, are formally only considered as four classes (Psilotopsida; Equisetopsida; Marattiopsida; Polypodiopsida), 11 orders and 37 families, without assigning a higher taxonomic rank.
Furthermore, within the Polypodiopsida, the largest grouping, a number of informal clades were recognised, including leptosporangiates, core leptosporangiates, polypods (Polypodiales), and eupolypods (including Eupolypods I and Eupolypods II).
These subclasses correspond to Smith's four classes, with Ophioglossidae corresponding to Psilotopsida.
In addition to these living groups, several groups of pteridophytes are now extinct and known only from fossils. These groups include the Rhyniopsida, Zosterophyllopsida, Trimerophytopsida, the Lepidodendrales and the Progymnospermopsida.
Modern studies of the land plants agree that all pteridophytes share a common ancestor with seed plants. Therefore, pteridophytes do not form a clade but constitute a paraphyletic group.
Just as with seed plants and mosses, the life cycle of pteridophytes involves alternation of generations. This means that a diploid generation (the sporophyte, which produces spores) is followed by a haploid generation (the gametophyte or prothallus, which produces gametes). Pteridophytes differ from mosses and seed plants in that both generations are independent and free-living, although the sporophyte is generally much larger and more conspicuous. The sexuality of pteridophyte gametophytes can be classified as follows:
These terms are not the same as monoecious and dioecious, which refer to whether a seed plant's sporophyte bears both male and female gametophytes, i. e., produces both pollen and seeds, or just one of the sexes.
Acrostichum is a fern genus in the Ceratopteridoideae subfamily of the Pteridaceae. It was one of the original pteridophyte genera delineated by Linnaeus. It was originally drawn very broadly, including all ferns that had sori apparently "acrostichoid", or distributed in a uniform mass across the back of the frond, rather than organized in discrete sori. This led Linnaeus to include such species as Asplenium platyneuron in the genus, because the specimen he received had sori so crowded that it appeared acrostichoid.
Since Acrostichum aureum is regarded as the type for the genus, it is now narrowly circumscribed only to the natural genus of three species, that are allied to the genus Ceratopteris. They are collectively known as the leather ferns or leather swamp ferns, genus members commonly being found in swamps. The species of Acrostichum are massive ferns, with fronds up to 12 feet (3.5 meters) tall, that depend on a semi-aquatic existence. They do not withstand prolonged immersion, but require wet roots. The species Acrostichum aureum is known to have a high saltwater tolerance, growing in mangroves.Diphasiastrum sitchense
Diphasiastrum sitchense, the Sitka clubmoss, is a pteridophyte species native to northern North America and northeastern Asia. It is a terrestrial herb spreading by stolons running on the surface or the ground or just slightly below the surface. Leaves are appressed, broadly lanceolate, up to 3.2 mm (0.13 inches) long. Strobili are solitary on the ends of shoots. It is known from every province in Canada, plus the US States of Alaska, Oregon, Washington, Idaho, Montana, Maine, New Hampshire, Vermont, and New York. It is also found in Greenland, St. Pierre and Miquelon, Yukon, Japan, and the Kamchatka Peninsula of Asiatic Russia. It can be found in alpine meadows, open rocky barrens, and coniferous woodlands.Equisetidae
Equisetidae is a subclass of Polypodiopsida (ferns). This subclass comprises the group commonly known as horsetails. It is equivalent to the class Equisetopsida sensu stricto in previous classifications.Isoetes appalachiana
Isoetes appalachiana, commonly known as the Appalachian quillwort (not to be confused with its close relative Isoetes engelmannii, which shares the same common name), is an aquatic pteridophyte that is widely distributed in the eastern United States. It is most frequently encountered in wetlands at low to middle elevations of the Appalachian Mountains in Pennsylvania, though its range extends from there south to Florida and Alabama along the eastern slopes of the mountains. It is a tetraploid and is grouped in the Isoetes engelmannii complex.Isoetes engelmannii
Isoetes engelmannii, commonly known as Engelmann's quillwort or Appalachian quillwort (not to be confused with the newly described Isoetes appalachiana), is an aquatic pteridophyte and is the most widely distributed species of its genus in eastern North America. Its range extends from Ontario in the north, south to Florida and west Arkansas and Missouri. It can be found from April to October in temporary pools, bogs, marshes, stream edges, swamps and along wet roadsides.Isoetes histrix
Isoetes histrix (land quillwort) is an aquatic pteridophyte native to the Mediterranean region, northwestern Africa, and the coasts of western Europe northwest to Cornwall. It occurs mainly in temporarily wet habitats, otherwise called vernal pools.
The leaves are 3–8 cm long, and summer-deciduous. It differs from Isoetes durieui by its large black scales between the leaves, though these are not always present, and a surface of megaspores with tubercles, whereas I durieui has a network of ridges.Isoetes melanospora
Isoetes melanospora, commonly known as black-spored quillwort or black-spored Merlin's grass, is a rare and endangered aquatic pteridophyte endemic to the U.S. states of Georgia and South Carolina. It grows exclusively in shallow, temporary pools on granite outcrops, often with only 2 cm of soil. 11 populations are known to exist in Georgia, while only one has been recorded in South Carolina, though this population is believed to be extirpated. The number of sites has dropped from 18 following its discovery due to habitat destruction caused by quarrying, trash dumping and trampling. New leaves quickly sprout after fall and winter rains, but during the dry summer months these typically shrivel.
Isoetes melanospora is a small plant growing in mud or shallow water but becoming terrestrial as the ground dries. Rootstock is nearly spherical. Leaves are up to 7 cm (2.8 inches) long, spirally arranged, tapering to the tip. Megaspores are gray or black, 350-480 μm in diameter. Microspores appear brown, each 26-31 μm across.The black-spored quillwort, a federally listed endangered species, is sometimes found growing with pool sprite (Amphianthus pusillus), another imperiled plant species. Both are protected at Stone Mountain in Georgia.Isoetes tegetiformans
Isoetes tegetiformans, commonly known as mat-forming quillwort or mat-forming Merlin's grass, is an aquatic pteridophyte endemic to the U.S. state of Georgia. It grows exclusively in shallow, temporary pools on granite outcrops, often with only 2 cm of soil. Only 7 populations are known to exist, and three of these have been destroyed since the plant's discovery in 1976. The remaining populations are threatened with habitat destruction due to quarrying, though the species is protected under the U.S. Endangered Species Act. New leaves quickly sprout after fall and winter rains, but during the dry summer months these typically shrivel.Leptosporangiate fern
Polypodiidae, commonly called leptosporangiate ferns, is a subclass of ferns. It is the largest group of living ferns, including some 11000 species worldwide. They constitute the subclass Polypodiidae, but are often considered to be the class Pteridopsida or Polypodiopsida, although other classifications assign them a different rank. The leptosporangiate ferns are one of the four major groups of ferns, with the other three being the Eusporangiate ferns comprising the marattioid ferns (Marattiidae, Marattiaceae), the horsetails (Equisetiidae, Equisetaceae), and whisk ferns and moonworts.There are approximately 8465 species of living leptosporangiate ferns, compared with about 2070 for all other ferns, totalling 10535 species of ferns. Almost a third of leptosporangiate fern species are epiphytes.These ferns are called leptosporangiate because their sporangia arise from a single epidermal cell and not from a group of cells as in eusporangiate ferns (a polyphyletic lineage). The sporangia are typically covered with a scale called the indusium, which can cover the whole sorus, forming a ring or cup around the sorus, or can also be strongly reduced to completely absent. Many leptosporangiate ferns have an annulus around the sporangium, which ejects the spores.Lindsaeineae
Lindsaeineae is a suborder of ferns (Polypodiopsida), order Polypodiales, created by the Pteridophyte Phylogeny Group (2016). It consists of two monogeneric families plus the larger Lindsaeaceae with seven genera, and the suborder contains about 237 species overall. It corresponds to Lindsaeaceae sensu Smith 2016.Marattiidae
The Marattiidae, also called marattioid ferns, are a subclass of class Polypodiopsida (ferns). This subclass comprises a single fern order, Marattiales, and family, Marattiaceae. It is equivalent to the class Marattiopsida in previous treatments, including Smith et al., 2006.Ophioglossaceae
Ophioglossaceae, the adder's-tongue family, is a family of ferns (though some studies have instead suggested a closer relationship to angiosperms), currently thought to be most closely related to Psilotaceae, the two together comprising the class Ophioglossidae as the sibling group to the rest of the ferns. The Ophioglossaceae is one of two groups of ferns traditionally known as eusporangiate ferns.Ophioglossales
Ophioglossales (lit. 'snake-tongue [plants]') are a small group of pteridophyte plants. Traditionally they were included in the ferns, originally as a family and later as the order Ophioglossales. In some classifications this group is placed in a separate division, the Ophioglossophyta, but recent molecular systematic studies have shown the Ophioglossales to be closely related to the Psilotales, and both are placed in the class Ophioglossidae.
In the molecular phylogenetic classification of Smith et al. in 2006, Ophioglossales, in its present circumscription, was placed with the order Psilotales in the class Psilotopsida. The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009) which placed all land plants in Equisetopsida, made it a member of subclass Ophioglossidae, equivalent to Smith's Psilotopsida. The placement of Ophioglossales in subclass Ophioglossidae has subsequently been followed in the classifications of Christenhusz and Chase (2014) and PPG I (2016).Older treatments have recognized segregate families within Ophioglossales such as Botrychiaceae for the moonworts and grape ferns and Helminthostachyaceae for Helminthostachys, but all modern treatments combine all members of the order into the single family Ophioglossaceae.The plants have short-lived spores formed in sporangia lacking an annulus, and borne on a stalk that splits from the leaf blade; and fleshy roots. Many species only send up one frond or leaf-blade per year. A few species send up the fertile spikes only, without any conventional leaf-blade. The gametophytes are subterranean. The spores will not germinate if exposed to sunlight, and the gametophyte can live some two decades without forming a sporophyte.
The genus Ophioglossum has the highest chromosome counts of any known plant. The record holder is Ophioglossum reticulatum, with about 630 pairs of chromosomes (1260 chromosomes per cell).Ophioglossidae
Ophioglossidae is a subclass of Polypodiopsida (ferns). This subclass consists of the ferns commonly known as whisk ferns, grape ferns, adder's-tongues and moonworts. It is equivalent to the class Psilotopsida in previous treatments, including Smith et al. (2006).Osmunda
Osmunda is a genus of primarily temperate-zone ferns of family Osmundaceae. Five to ten species have been listed for this genus.Polypodiales
The order Polypodiales encompasses the major lineages of polypod ferns, which comprise more than 80% of today's fern species. They are found in many parts of the world including tropical, semitropical and temperate areas.Prothallium
A prothallium, or prothallus (from Latin pro = forwards and Greek θαλλος (thallos) = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young gametophyte of a liverwort or peat moss as well.
The prothallium develops from a germinating spore. It is a short-lived and inconspicuous heart-shaped structure typically 2–5 millimeters wide, with a number of rhizoids (root-like hairs) growing underneath, and the sex organs: archegonium (female) and antheridium (male). Appearance varies quite a lot between species. Some are green and conduct photosynthesis while others are colorless and nourish themselves underground as saprotrophs.Pteridaceae
Pteridaceae is a family of ferns in the order Polypodiales., including some 1150 known species in ca 45 genera (depending on taxonomic opinions), divided over five subfamilies. The family includes four groups of genera that are sometimes recognized as separate families: the adiantoid, cheilanthoid, pteroid, and hemionitidoid ferns. Relationships among these groups remain unclear, and although some recent genetic analyses of the Pteridales suggest that neither the family Pteridaceae nor the major groups within it are all monophyletic, as yet these analyses are insufficiently comprehensive and robust to provide good support for a revision of the order at the family level.Saccolomataceae
Saccolomataceae is a family of ferns in the order Polypodiales. It has been formerly treated as part of the Dennstaedtiaceae, however it has been classified as its own family according to Smith et al. (2006) The genus Saccoloma has been classified to include Orthiopteris, but the phylogeny of the group not yet fully understood. The family includes a dozen known species.
|Plant growth and habit|
Extant Life phyla/divisions by domain