Ophioglossaceae
Encyclopedia
Ophioglossaceae, the Adder's tongue family, is a family of fern
s, currently thought to be most closely related to Psilotaceae
, the two together comprising the class Psilotopsida
as the sibling group
to the rest of the ferns. The Ophioglossaceae is one of two groups of ferns traditionally known as eusporangiate fern
. The number of genera
included in the family varies between different authors' treatments, and most conservatively the family is treated as containing four genera, Ophioglossum
, Botrychium, Helminthostachys
, and Mankyua
(placed in two to four separate families in other treatments). A broad definition of the family and its genera have been taken in several recent treatments (e.g., Wagner 1990, Smith et al. 2006, and in the Flora of North America). A notable exception is the classification of Kato (1987), who advocated the division of Botrychium into four genera: Botrychium s.s., Sceptridium, Japanobotrychium, and Botrypus.
These ferns differ from the other ferns in several respects:
Members of Ophioglossaceae are usually terrestrial (excepting a few epiphytic
species of Ophioglossum) and occur in both temperate
and tropical areas. The leaves are usually fleshy, and in temperate areas will often turn brownish or reddish during colder months. In addition to having mycoheterotrophic gametophytes, there are a few members of Botrychium that are unique among ferns in having the sporophyte
s also mycoheterotrophic, producing only small, ephemeral sporophylls that do not photosynthesize.
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, currently thought to be most closely related to Psilotaceae
Psilotaceae
Psilotaceae is a family of fern-like plants consisting of two genera, Psilotum and Tmesipteris. The two genera are very different and in the past Tmesipteris has been placed in its own family, Tmesipteridaceae, but most classifications continue to treat it in Psilotaceae...
, the two together comprising the class Psilotopsida
Psilotopsida
Psilotopsida is a class of fern-like plants. It should not be confused with the obsolete class Psilophytopsida. As circumscribed by Smith et al. Psilotopsida contains two families, Psilotaceae and Ophioglossaceae, placed in orders Psilotales and Ophioglossales, respectively...
as the sibling group
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
to the rest of the ferns. The Ophioglossaceae is one of two groups of ferns traditionally known as eusporangiate fern
Eusporangiate fern
Eusporangiate ferns are vascular spore plants, whose sporangia arise from several epidermal cells and not from a single cell as in leptosporangiate ferns...
. The number of genera
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
included in the family varies between different authors' treatments, and most conservatively the family is treated as containing four genera, Ophioglossum
Ophioglossum
Ophioglossum is a genus of about 25-30 species of Ophioglossales in the family Ophioglossaceae, with a cosmopolitan but primarily tropical and subtropical distribution. The name Ophioglossum comes from the Greek, and means "snake-tongue".Adders-tongues are so-called because the spore-bearing stalk...
, Botrychium, Helminthostachys
Helminthostachys
Helminthostachys zeylanica is a terrestrial, herbaceous, fern-like plant of southeastern Asia and Australia, commonly known as Kamraj and tunjuk-langit...
, and Mankyua
Mankyua
Mankyua is a recently-discovered plant, a single species in its own genus. It is a fern in the Ophioglossales. Its only species, M. chejuense , grows only on a small Korean island, Cheju Island....
(placed in two to four separate families in other treatments). A broad definition of the family and its genera have been taken in several recent treatments (e.g., Wagner 1990, Smith et al. 2006, and in the Flora of North America). A notable exception is the classification of Kato (1987), who advocated the division of Botrychium into four genera: Botrychium s.s., Sceptridium, Japanobotrychium, and Botrypus.
These ferns differ from the other ferns in several respects:
- they produce only a single leafLeafA leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
at a time - instead of the leptosporangiaSporangiumA sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
typical of most ferns they produce eusporangia, which are larger, contain more spores, and have thicker walls - their sporophyllSporophyllA sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls bear either megasporangia , or microsporangia...
s are divided into two distinct parts, the sporophore which produces sporangia and has a greatly reduced and modified blade, and the trophophore, which is very similar to the trophophylls in size, color, shape, and so forth - their gametophyteGametophyteA gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
s are subterranean and rely on fungiFungusA fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
for their energy (in other words, they are mycoheterotrophic), unlike the terrestrialTerrestrial plantA terrestrial plant is one that grows on land. Other types of plants are aquatic , epiphytic , lithophytes and aerial ....
, photosyntheticPhotosynthesisPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
gametophytes found in most ferns.
Members of Ophioglossaceae are usually terrestrial (excepting a few epiphytic
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...
species of Ophioglossum) and occur in both temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
and tropical areas. The leaves are usually fleshy, and in temperate areas will often turn brownish or reddish during colder months. In addition to having mycoheterotrophic gametophytes, there are a few members of Botrychium that are unique among ferns in having the sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
s also mycoheterotrophic, producing only small, ephemeral sporophylls that do not photosynthesize.