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
Pteridophytes (ferns and lycophytes) are free-sporing vascular plants that have a life cycle with alternating, free-living gametophyte and sporophyte phases that are independent at maturity. 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 bryophytes and spermatophytes (seed plants), 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 bryophytes in that the sporophyte is branched and generally much larger and more conspicuous, and from seed plants in that both generations are independent and free-living. 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.
Blechnaceae is a family of ferns, with a cosmopolitan distribution. Its status as a family and the number of genera included have both varied considerably. The influential Pteridophyte Phylogeny Group in their 2016 classification accept 24 genera.Drynarioideae
Drynarioideae is a subfamily of the Polypodiaceae family of ferns.
It combines the drynarioid and selligueoid ferns, which have been considered to be tribes (Drynarieae Subh.Chandra 1982 and Selligueeae (author?)) of the Polypodioideae subfamily of Polypodiaceae, but recent molecular phylogenic analysis have placed them in a separate subfamily. The genus count of neither of original tribes was certain, but the combined total is probably at least nine. The Pteridophyte Phylogeny Group classification of 2016 (PPG I) recognizes six genera:
Arthromeris (T.Moore) J.Sm.
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.Hypodematiaceae
Hypodematiaceae is a family of ferns in the order Polypodiales. It consists of two, or in some versions three, small genera. Hypodematium and Leucostegia are included in the Pteridophyte Phylogeny Group classification (PPG I). Didymochlaena can be placed in this family as well, but in PPG I, it is placed in its own family, Didymochlaenaceae.Hypodematiaceae was erected by Ren-Chang Ching in 1975, but was not subsequently accepted by many authors. It was not accepted in a classification of ferns that was published in 2006. In that paper, the genera Hypodematium, Leucostegia, and Didymochlaena were provisionally assigned to Dryopteridaceae, with the authors expressing some doubt about whether they really belonged there. In two molecular phylogenetic studies published in 2007, the clade that was tentatively called eupolypods I was resolved as a tritomy consisting of Didymochlaena, Hypodematiaceae sensu stricto, and the rest of eupolypods I.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.Lomariopsidaceae
The Lomariopsidaceae is a family of ferns with a largely tropical distribution. It is placed in the suborder Aspleniineae (eupolypods I) of the order Polypodiales. The Pteridophyte Phylogeny Group classification of 2016 (PPG I) included four genera. A fifth, Dryopolystichum, was added in 2017.
ThysanosoriaThe genus Nephrolepis has also been placed in this family, but it is now placed in its own family, Nephrolepidaceae. As of August 2019, Plants of the World Online sinks Lomariopsidaceae into a very widely circumscribed Polypodiaceae.Some members of the Lomariopsidaceae are cultivated as ornamental plants.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.Nephrolepis
Nephrolepis is a genus of about 30 species of ferns. It is the only genus in the family Nephrolepidaceae, placed in the suborder Aspleniineae (eupolypods I) of the order Polypodiales in the Pteridophyte Phylogeny Group classification of 2016 (PPG I). (It is placed in the Dryopteridaceae in some other classifications.) The genus is commonly referred to as macho ferns or swordferns.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 one of the four subclasses 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). The subclass contains two orders, Psilotales and Ophioglossales, whose relationship was only confirmed by molecular phylogenetic studies.Platycerioideae
Platycerioideae is a subfamily of the Polypodiaceae family of ferns. The Pteridophyte Phylogeny Group classification of 2016 (PPG I) recognizes two genera:
Polypodiaceae is a family of ferns. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the family includes around 65 genera and an estimated 1,650 species and is placed in the order Polypodiales, suborder Polypodiineae. A broader circumscription has also been used, in which the family includes other families kept separate in PPG I. Nearly all species are epiphytes, but some are terrestrial.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.Pteridophyte Phylogeny Group
The Pteridophyte Phylogeny Group, or PPG, is an informal international group of systematic botanists who collaborate to establish a consensus on the classification of pteridophytes (lycophytes and ferns) that reflects knowledge about plant relationships discovered through phylogenetic studies. In 2016, the group published a classification for extant pteridophytes, termed "PPG I". The paper had 94 authors (26 principal and 68 additional).Schizaeaceae
Schizaeaceae is a family of ferns in the order Schizaeales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it includes only two genera. Alternatively, two families kept separate in PPG I, Lygodiaceae and Anemiaceae, may be included in Schizaeaceae as subfamilies.Species are mainly distributed in the tropics, but several are found in temperate regions in North America, South Africa, Australasia and Northeast Asia. The sporangia are borne on specialised pinnae, distinct from ordinary vegetative pinnae. The pinnae form small comb-like, pinnate structures on which the sporangia are formed.
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Extant Life phyla/divisions by domain