instance_of ophioglossum
Psilotaceae is a ___MASK77___ of Pteridophyta ( in ___MASK14___ Psilotales ) consisting of two genera , " Psilotum " and " Tmesipteris " with a dozen species . In ___MASK17___ , a ___MASK81___ complex is a group of closely related ___MASK81___ that are very similar in appearance to the ___MASK2___ that the boundaries between them are often unclear . Terms sometimes used synonymously but with more precise meanings are : cryptic ___MASK81___ for two or more ___MASK81___ hidden under one ___MASK81___ name , sibling ___MASK81___ for two cryptic ___MASK81___ that are each other ' s closest relative , and ___MASK81___ flock for a group of closely related ___MASK81___ living in the same habitat . As informal taxonomic ranks , ___MASK81___ group , ___MASK81___ aggregate , and superspecies are also in use . In ___MASK100___ , subspecies ( abbreviated " subsp ." or " ssp ."; " plural ": " subspecies ") is either a taxonomic rank subordinate to species , or a taxonomic unit in that rank . A subspecies cannot be recognized independently : a species ___MASK57___ either be recognized as having no subspecies at all or at least two ( including any that are extinct ). In ___MASK17___ , an ___MASK97___ is any contiguous living system , such as an animal , plant , fungus , archaeon , or bacterium . All known types of organisms are capable of some degree of response to stimuli , reproduction , growth and development and homeostasis . An ___MASK97___ consists of one or more cells ; when it has one cell it is known as a unicellular ___MASK97___ ; and when it has more than one it is known as a multicellular ___MASK97___ . Most unicellular organisms are of microscopic scale and are thus loosely described as microorganisms . Humans are multicellular organisms composed of many trillions of cells grouped into specialized tissues and organs . A fern is a ___MASK49___ of a group of about 10 , 560 known extant species of vascular plants that reproduce via spores and have neither seeds nor flowers . They differ from mosses by being vascular , i . e ., having certain tissue that conducts ___MASK35___ and nutrients . They have branched stems and leaves like other vascular plants . These are " megaphylls ", which are more complex than the simple " microphylls " of clubmosses . Most ferns are Leptosporangiate ferns , sometimes denominated the " true ferns ": they produce what are called " fiddleheads " that uncoil and expand into fronds . A ___MASK30___ ( genera ) is a taxonomic rank used in the ___MASK100___ of living and fossil organisms in biology . In the ___MASK48___ of ___MASK100___ , ___MASK30___ comes above species and below family . In binomial nomenclature , the ___MASK30___ ___MASK64___ forms the first ___MASK56___ of the binomial species ___MASK64___ for each species within the ___MASK30___ . Binomial ___MASK72___ ( also called binominal ___MASK72___ or binary ___MASK72___ ) is a formal ___MASK4___ of naming species of living things by giving each a name composed of two parts , both of which use Latin grammatical forms , although they can be based on words from other languages . Such a name is called a binomial name ( which may be shortened to just " binomial "), a binomen or a scientific name ; more informally it is also called a Latin name . The first part of the name identifies the genus to which the species belongs ; the second part identifies the species within the genus . For example , humans belong to the genus " Homo " and within this genus to the species " Homo sapiens ". The " formal " introduction of this ___MASK4___ of naming species is credited to Carl Linnaeus , effectively beginning with his work " Species Plantarum " in 1753 . But Gaspard Bauhin , in as early as 1623 , had introduced in his book " Pinax theatri botanici " ( English , " Illustrated exposition of plants ") many names of genera that were later adopted by Linnaeus . Sexual ___MASK24___ is a form of ___MASK24___ where ___MASK1___ morphologically distinct types of specialized reproductive cells called gametes fuse together , involving a female ' s large ovum ( or egg ) and a male ' s smaller sperm . Each ___MASK78___ contains half the number of chromosomes of normal cells . They are created by a specialized type of ___MASK84___ division , which only occurs in eukaryotic cells , known as meiosis . The ___MASK1___ gametes fuse during fertilization to produce ___MASK47___ replication and the creation of a ___MASK91___ - celled zygote which includes genetic material from both gametes . In a process called genetic recombination , genetic material ( ___MASK47___ ) joins up so that homologous chromosome sequences are aligned with each other , and this is followed by exchange of genetic information . Two rounds of ___MASK84___ division then produce four daughter cells with half the number of chromosomes from each original parent ___MASK84___ , and the same number of chromosomes as both parents , though self - fertilization can occur . For instance , in human ___MASK24___ each human ___MASK84___ contains 46 chromosomes , 23 pairs , except ___MASK78___ cells , which only contain 23 chromosomes , so the child will have 23 chromosomes from each parent genetically recombined into 23 pairs . Cell division initiates the development of a new individual ___MASK97___ in multicellular organisms , including animals and plants , for the vast majority of whom this is the primary method of ___MASK24___ . ___MASK17___ is a natural ___MASK18___ concerned with the study of life and living organisms , including their ___MASK34___ , function , growth , evolution , distribution , identification and taxonomy . Modern biology is a vast and eclectic ___MASK96___ , composed of many branches and subdisciplines . However , despite the broad scope of biology , there are certain general and unifying concepts within it that govern all study and research , consolidating it into ___MASK91___ , coherent ___MASK96___ . In general , biology recognizes the cell as the basic unit of life , genes as the basic unit of heredity , and evolution as the engine that propels the synthesis and creation of new species . It is also understood today that all the organisms survive by consuming and transforming energy and by regulating their internal environment to maintain a stable and vital condition known as homeostasis . In ___MASK100___ , rank is the relative level of a group of organisms ( a ___MASK74___ ) in a taxonomic hierarchy . Examples of taxonomic ranks are species , genus , family , order , class , phylum , kingdom , domain , etc . ___MASK22___ is a standard protocol for allowing serial ___MASK54___ for telecommunications programs under the ___MASK38___ ___MASK39___ . ___MASK22___ is an acronym for " Fido Opus SEAdog Standard Interface Layer ". " Fido " refers to FidoBBS , " Opus " refers to Opus - CBCS BBS , and " SEAdog " refers to a Fidonet compatible mailer . The standards document that defines the ___MASK22___ protocol is maintained by the Fidonet Technical Standards Committee . Ophioglossum , the adder ' s - tongue ferns , is a ___MASK30___ of about 25 - 30 species of ferns in the family Ophioglossaceae , of the order Ophioglossales . The name Ophioglossum comes from the Greek , and means `` snake - tongue '' . Their cosmopolitan distribution is mainly in tropical and subtropical habitats . In ___MASK17___ , a ___MASK74___ ( plural taxa ; back - formation from " taxonomy ") is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit . Although neither is required , a ___MASK74___ is usually known by a particular name and given a particular ranking , especially if and when it is accepted or becomes established . It is not uncommon , however , for taxonomists to remain at odds over what belongs to a ___MASK74___ and the criteria used for inclusion . If a ___MASK74___ is given a formal scientific name , its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping . Eusporangiate ferns are vascular spore plants , whose sporangia arise from several epidermal cells and not from a ___MASK91___ cell as in leptosporangiate ferns . Typically these ferns have reduced root systems and sporangia that produce large amounts of spores ( up to 7000 spores per sporangium in " Christensenia ") Ophioglossaceae , the adder ' s - tongue ___MASK77___ , is a ___MASK77___ of ferns ( though some studies have instead suggested a closer ___MASK42___ to angiosperms ), 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 ferns . Ophioglossales ( lit . ' snake - tongue [ plants ]') are a small ___MASK7___ of pteridophyte plants . Traditionally they are included in the ___MASK80___ Pteridophyta , the ferns , originally as a ___MASK77___ and later as the ___MASK14___ Ophioglossales . In some classifications this ___MASK7___ is placed in a separate ___MASK80___ , the Ophioglossophyta , but recent molecular systematic studies have shown the Ophioglossales to be closely related to the Psilotales . In ___MASK17___ , ___MASK27___ are the young born of living organisms , produced either by a ___MASK91___ ___MASK97___ or , in the case of sexual reproduction , two organisms . Collective ___MASK27___ may be known as a brood or progeny in a more general way . This can refer to a set of simultaneous ___MASK27___ , such as the chicks hatched from one clutch of eggs , or to all the ___MASK27___ , as with the honeybee . Psilotopsida is a ___MASK31___ of ferns or fern - like plants , considered to be one of the three classes of eusporangiate ferns . It should not be confused with the obsolete ___MASK31___ Psilophytopsida . As circumscribed by Smith " et al .", 2006 , Psilotopsida contains ___MASK1___ families , Psilotaceae and Ophioglossaceae , placed in orders Psilotales and Ophioglossales , respectively . The affinities of these ___MASK1___ groups have long been unclear and a close ___MASK42___ between them has only recently been confirmed through molecular systematic studies . Some studies ___MASK50___ that Psilotopsida is the sister - group to all other ferns ( including Marattiaceae and Equisetaceae ), but others indicate that Equisetaceae is more basal . Deoxyribonucleic ___MASK75___ ( DNA ) is a ___MASK68___ that carries the genetic instructions used in the growth , development , functioning and reproduction of all known living organisms and many viruses . DNA and RNA are nucleic acids ; alongside proteins , lipids and complex carbohydrates ( polysaccharides ), they are one of the four major types of macromolecules that are essential for all known forms of life . Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix . In ___MASK17___ , a ___MASK81___ ( abbreviated sp ., with the plural form ___MASK81___ abbreviated spp .) is the basic unit of ___MASK100___ and a taxonomic rank . A ___MASK81___ is often defined as the largest group of organisms in which two individuals can produce fertile ___MASK27___ , typically by sexual reproduction . While this definition is often adequate , looked at more closely it is often problematic . For example , in a ___MASK81___ complex , the boundaries between closely related ___MASK81___ become unclear or disappear altogether . Other ways of defining ___MASK81___ include similarity of DNA , morphology , or ecological niche . The presence of locally adaptive traits may further subdivide ___MASK81___ into infraspecific taxa such as subspecies . A pteridophyte " sensu lato " is a vascular ___MASK60___ ( with xylem and phloem ) that reproduces via spores , and therefore was a ___MASK49___ of the former and now invalid ___MASK74___ denominated Pteridophyta ; the denomination " sensu stricto " presently only has informal use to denominate a monilophyte ( fern ) or lycophyte , or simply and only a monilophyte . Because pteridophytes produce neither flowers or seeds , they are also denominated " cryptogams ". 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 now an invalid ___MASK74___ . In ecology , a niche is a ___MASK95___ with a ___MASK69___ of meanings related to the ___MASK33___ of a species living under specific environmental conditions . The ecological niche describes how an ___MASK97___ or population responds to the distribution of resources and competitors ( for example , by growing when resources are abundant , and when predators , parasites and pathogens are scarce ) and how it in turn alters those same factors ( for example , limiting access to resources by other organisms , acting as a food source for predators and a consumer of prey ). " The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [ and ] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts ".