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.
Smith et al. (2006) carried out the first higher-level pteridophyte classification published in the molecular phylogenetic era, and considered the ferns (monilophytes), with four classes. They placed the whisk ferns and related taxa in the class Psilotopsida, with two orders. Mark W. Chase and James L. Reveal (2009) classified them as two separate subclasses, Psilotidae and Ophioglossidae, corresponding to those orders within a much broader grouping, the class Equisetopsida sensu lato. Christenhusz et al., 2011, included both the Ophioglossales and Psilotales orders in the Ophioglossidae subclass. This was continued by both Christenhusz and Chase (2014) and by the Pteridophyte Phylogeny Group (2016). Under the latter the subclass is one of four subclasses of Polypodiopsida (ferns) and contains two orders, two families, 12 genera, and an estimated 129 species. The relationships between the two orders, Psilotales and Ophioglossales, has long been unclear and was only confirmed by molecular systematic studies. Psilotales have rhizoids instead of real roots, and the roots in Ophioglossales are lacking both root branches and root hairs. The gametophytes of both orders are heterotrophic and often subterranean, getting nutrients from mycorrhiza instead of performing photosynthesis, which happens exclusively in the sporophyte.
The following cladogram shows a likely phylogenic relationship between subclass Ophioglossidae and the other Polypodiopsida subclasses. The first three small subclasses are sometimes informally referred to as eusporangiate ferns, in contrast to the largest subclass, Polypodiidae or leptosporangiate ferns.
Cyanidiophytina is a subdivision of red algae.In older texts it was described as an order "Cyanidiales". It was granted division status in the Saunders and Hommersand 2004 classification (as "Cyanidophyta"), but was only elevated to subdivision Cyanidiophytina in the Yoon et al. classification of 2006.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.Equisetopsida sensu lato
Equisetopsida is the name of a class of plants that traditionally contains the single genus Equisetum (horsestails). However, in 2009, in an article titled "A phylogenetic classification of the land plants to accompany APG III," Mark W. Chase and James L. Reveal proposed a much broader sense for the Equisetopsida class name. In their system, Equisetopsida includes all land plants (embryophytes). Their rationale was that "If the major clades of green algae are recognized as classes, then all land plants, the embryophytes, should be included in a single class..."Fern
A fern is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissues that conduct water and nutrients and in having life cycles in which the sporophyte is the dominant phase. Ferns have complex leaves called megaphylls, that are more complex than the microphylls of clubmosses. Most ferns are leptosporangiate ferns, sometimes referred to as true ferns. They produce coiled fiddleheads that uncoil and expand into fronds. The group includes about 10,560 known extant species.Ferns are defined here in the broad sense, being all of the Polypodiopsida, comprising both the leptosporangiate (Polypodiidae) and eusporangiate ferns, the latter itself comprising ferns other than those denominated true ferns, including horsetails or scouring rushes, whisk ferns, marattioid ferns, and ophioglossoid ferns.
Ferns first appear in the fossil record about 360 million years ago in the late Devonian period, 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. The fern Osmunda claytoniana is a paramount example of evolutionary stasis; paleontological evidence indicates it has remained unchanged, even at the level of fossilized nuclei and chromosomes, for at least 180 million years.Ferns are not of major economic importance, but some are used for food, medicine, as biofertilizer, as ornamental plants and for remediating contaminated soil. They have been the subject of research for their ability to remove some chemical pollutants from the atmosphere. Some fern species, such as bracken (Pteridium aquilinum) and water fern (Azolla filiculoides) are significant weeds world wide. Some fern genera, such as Azolla can fix nitrogen and make a significant input to the nitrogen nutrition of rice paddies. They also play certain roles in mythology and art.Galdieriaceae
Galdieriaceae is a family of red algae, one of two families in the order Cyanidiales.Ginkgoidae
Ginkgoidae is a subclass of Equisetopsida in the sense used by Mark W. Chase and James L. Reveal in their 2009 article "A phylogenetic classification of the land plants to accompany APG III." This subclass contains the single extant genus Ginkgo under order Ginkgoales, family Ginkgoaceae. Its only extant species is Ginkgo biloba, the Maidenhair Tree.Gnetidae
Gnetidae is a subclass of Equisetopsida in the sense used by Mark W. Chase and James L. Reveal in their 2009 article "A phylogenetic classification of the land plants to accompany APG III." This subclass comprises the gnetophytes. The Gnetidae subclass is equivalent to the division Gnetophyta and class Gnetopsida of previous treatments.Horneophytopsida
Horneophytopsida is a class of extinct plants which consisted of branched stems without leaves, true roots or vascular tissue, found from the Late Silurian to the Early Devonian (around 430 to 390 million years ago). They are the simplest known polysporangiophytes, i.e. plants with sporophytes bearing many spore-forming organs (sporangia) on branched stems. They were formerly classified among the rhyniophytes, but it was later found that some of the original members of the group had simple vascular tissue and others did not.In 2004, Crane et al. published a cladogram for the polysporangiophytes in which the Horneophytopsida are shown as the sister group of all other polysporangiophytes. One other former rhyniophyte, Aglaophyton, is also placed outside the tracheophyte clade, as it did not possess true vascular tissue (in particular did not have tracheids), although its conducting tissue is more complex than that of the Horneophytopsida.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.Lycopodiidae
Lycopodiidae is a subclass of Equisetopsida in the sense used by Mark W. Chase and James L. Reveal in their 2009 article "A phylogenetic classification of the land plants to accompany APG III." This subclass comprises the lycopods. It is equivalent to the division Lycopodiophyta in previous classifications.Lycopodiopsida
Lycopodiopsida is a class of herbaceous vascular plants known as the clubmosses and firmosses. They have dichotomously branching stems bearing simple leaves called microphylls and reproduce by means of spores borne in sporangia at the bases of the leaves. Traditionally, the group also included the spikemosses (Selaginella and relatives) and the quillworts (Isoetes and relatives) but because these groups have leaves with ligules and reproduce using spores of two different sizes, both are now placed into another class, Isoetopsida that also includes the extinct Lepidodendrales. These groups, together with the horsetails are often referred to informally as fern allies.
The class Lycopodiopsida as interpreted here contains a single living order, the Lycopodiales, and a single extinct order, the Drepanophycales.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).Pinidae
Pinidae is a subclass of Equisetopsida in the sense used by Mark W. Chase and James L. Reveal in their 2009 article "A phylogenetic classification of the land plants to accompany APG III." This subclass comprises the conifers. The Pinidae subclass is equivalent to the division Pinophyta and class Pinopsida of previous treatments.Psilotaceae
Psilotaceae is a family of ferns (class Polypodiopsida) (in order Psilotales) consisting of two genera, Psilotum and Tmesipteris with a dozen species.Pteridophyte
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.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).Streptophyta
Streptophyta, informally the streptophytes (from the Greek strepto, for twisted, i.e., the morphology of the sperm of some members), is a clade of plants. The composition of the clade varies considerably between authors, but the definition employed here includes land plants and all green algae except the Chlorophyta and possibly the more basal Mesostigmatophyceae, Chlorokybophyceae, and Spirotaenia.