| Ophioglossaceae | |
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| Ophioglossum vulgatum | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Division: | Polypodiophyta |
| Class: | Polypodiopsida |
| Subclass: | Ophioglossidae |
| Order: | Ophioglossales Link[1] |
| Family: | Ophioglossaceae Martinov[1] |
| Subfamilies and genera | |
| Synonyms | |
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Ophioglossaceae, fromAncient Greek ὄφις (óphis), meaning "snake", and γλῶσσα (glôssa), meaning "tongue", also known as theadder's-tongue family, is a small family offerns. In thePteridophyte Phylogeny Group classification of 2016 (PPG I), it is the only family in the orderOphioglossales, which together with thePsilotales is placed in the subclassOphioglossidae.[1] The Ophioglossidae are one of the groups traditionally known aseusporangiate ferns. Members of the family differ from other ferns in a number of ways. Many have only a single fleshy leaf at a time. Theirgametophytes are subterranean and rely onfungi for energy.
Members of Ophioglossaceae are usually terrestrial (excepting a fewepiphytic species ofOphioglossum) and occur in bothtemperate andtropical areas. They differ from the other ferns in several respects:
In addition to having mycoheterotrophic gametophytes, there are a few members ofBotrychium that are unique among ferns in having thesporophytes also mycoheterotrophic, producing only small, ephemeral sporophylls that do not photosynthesize.
Botrychium andHelminthostachys are also the only known ferns withsecondary growth, even if it is very limited.[2]
The plants have short-livedspores formed insporangia lacking anannulus, and borne on a stalk that splits from the leaf blade; and fleshyroots. A few species send up fertile spikes only, without any conventional leaf-blade. The spores will not germinate if exposed to sunlight, and the gametophyte can live some two decades without forming asporophyte.
The genusOphioglossum has the highestchromosome counts of any known plant. The record holder isOphioglossum reticulatum, with about 630 pairs of chromosomes (1260 chromosomes per cell).[3] Other measurements have indicated a chromosome number up to 1440 (n = 720).[4] For comparison, humans have 46 chromosomes, consisting of n = 23pairs.
Ophioglossum malviae from the Western Ghats in India has been characterized as the world's smallest terrestrial pteridophyte with plants typically 1–1.2 cm in size.[5]
The ferns in this group were originally treated as a family and later as the separate order Ophioglossales. In some classifications, they were placed in a separate division, Ophioglossophyta, but molecular phylogenetic studies have shown the Ophioglossales to be closely related to thePsilotales, and both are placed in the classOphioglossidae.
In the molecular phylogenetic classification of Smith et al. in 2006, Ophioglossales, in its present circumscription, was placed in the class Psilotopsida, along with the order Psilotales.[6] The linear sequence of Christenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009),[7] which placed all land plants in Equisetopsida,[8] made it a member of subclass Ophioglossidae, equivalent to Smith's Psilotopsida.[7] This approach has subsequently been followed in the classifications of Christenhusz and Chase (2014)[9] and PPG I (2016).[1]
Older treatments recognized segregate families within the Ophioglossales, such as Botrychiaceae for themoonworts andgrape ferns and Helminthostachyaceae forHelminthostachys, but modern treatments combine all members of the order into the single family Ophioglossaceae.[6][7][9][1]
| Phylogeny of Ophioglossaceae[10] | |||||||||||||||||||||||||||
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| Phylogeny of Ophioglossaceae[11][12] | |||||||||||||||||||||||||||||||||||||||||||||||||||
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The number of genera into which the family is divided has varied. The Smith system of 2006 used four genera, treatingBotrychium andOphioglossum broadly.[6]Cheiroglossa has been segregated fromOphioglossum,[7] or included within it.[9] The PPG I system of 2016 divides the family into four subfamilies:[1]
Classification ofArchaeplastida orPlantaes.l. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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