''Takakia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of two species of mosses known from western North America and central and eastern

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

. The genus is placed as a separate

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

, order and

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

among the mosses. It has had a history of uncertain placement, but the discovery of sporophytes clearly of the moss-type firmly supports placement with the mosses.

Discovery

''Takakia'' was discovered in the

Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...

and described by

William Mitten William Mitten (30 November 1819 – 20 July 1906), was an English pharmaceutical chemist and authority on bryophytes who has been called "the premier bryologist of the second half of the nineteenth century". He built up a collection of some ...

in 1861. It was originally described simply as a new

liverwort The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of ...

species (''

Lepidozia ''Lepidozia'' is a genus of liverwort The Marchantiophyta () are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells ...

ceratophylla'')Renzaglia, K. S., K. D. McFarland, & D. K. Smith. 1997. Anatomy and ultrastructure of the sporophyte of ''Takakia ceratophylla'' (Bryophyta). ''American Journal of Botany'' 84(10): 1337–1350. within an existing genus, and it was thus long overlooked. The discovery of similar odd plants in the mid-20th century by Dr. Noriwo Takaki (1915–2006) in Japan sparked more interest. The many unusual features of these plants led to the establishment in 1958 of the species ''Takakia lepidozioides'', in a new genus ''Takakia'', named to honor the man who rediscovered it and recognized its unique characteristics. The species originally described by Mitten was subsequently recognized by Grolle as belonging to this new genus, and accordingly renamed ''Takakia ceratophylla''. All of the plants originally collected lacked any reproductive structures; they were sterile

gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...

plants. Eventually, plants with archegonia were found, which resembled the archegonia found in mosses. Fertile plants bearing

antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...

and sporophytes were first reported in 1993 from the

Aleutian Islands The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...

, and both structures were clearly of the form found in primitive mosses. This discovery established ''Takakia'' as a genus of moss, albeit an unusual one. In

, ''Takakia'' has since been found in

Sikkim Sikkim (; ) is a state in Northeastern India. It borders the Tibet Autonomous Region of China in the north and northeast, Bhutan in the east, Province No. 1 of Nepal in the west and West Bengal in the south. Sikkim is also close to the Silig ...

(in the

), North Borneo,

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

, and Japan. In North America, the genus is found in the

and

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

.Hong, Won Shic. 1987. "The Distribution of Western North American Hepaticae. Endemic Taxa and Taxa with a North Pacific Arc Distribution". ''The Bryologist'' 90 (4): 344–361. It occurs in a variety of local habitats, from bare rock, to moist humus, and grows at elevations ranging from

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...

to the

subalpine Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial f ...

Description

''Takakia'' is the oldest known extant genus of land plants. They secrete a microbe-harboring

mucilage Mucilage is a thick, gluey substance produced by nearly all plants and some microorganisms. These microorganisms include protists which use it for their locomotion. The direction of their movement is always opposite to that of the secretion of m ...

to establish a diverse

microbiome A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably wel ...

containing microbes associated with

nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

and mycorrhiza.Microbiome and related structural features of Earth’s most archaic plant indicate early plant symbiosis attributes
/ref> The plant's Japanese name (''nanjamonja-goke'') "impossible moss" reflects this.Schofield, W. B. 1985. ''Introduction to Bryology'', pages 143–154. (New York: Macmillan). . It was believed to have the lowest known

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

count (''n''=4) per cell of any

land plant The Embryophyta (), or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes () have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sist ...

,Schuster, Rudolf M. 1966. ''The Hepaticae and Anthocerotae of North America'', volume I, pages 262–263. (New York: Columbia University Press). but some plants of the small Australian daisy ''Brachyscome dichromosomatica'' are now known to have a count of ''n''=2.Carter C.R. 1978. Taxonomy of the ''Brachycome lineariloba'' complex (Asteraceae). ''Telopea'', volume 5, pages 387–393. From a distance, ''Takakia'' looks like a typical layer of moss or

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

e on the rock where it grows. On closer inspection, tiny shoots of ''Takakia'' grow from a turf of slender, creeping rhizomes. The green shoots which grow up from the turf are seldom taller than 1 cm, and bear an irregular arrangement of short, finger-like leaves (1 mm long). These leaves are deeply divided into two or more filaments, a characteristic not found in any other moss.Buck, William R. & Bernard Goffinet. 2000. "Morphology and classification of mosses", pages 71–123 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press). . Both the green shoots and their leaves are very brittle. Unlike in other

bryophyte The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited in s ...

s, the egg-producing archegonia and sperm-producing

are not surrounded by perichaetial leaves or other protective tissues. Instead, the gametangia are naked in the angle formed between the stem and the vegetative leaves. The sporophyte develops a long stalk ending in an elongated spore capsule. The capsule contains a central columella over and around which the spores are produced. When the sporophyte is mature, the capsule ruptures along a single spiral slit to release the spores.

Classification

References

External links

* J. R. Spence & W. B. Schofield. 2005. ''Bryophyte Flora of North America''
Takakiaceae
{{Taxonbar, from=Q80293 Moss genera Takakiopsida