Takakia
Encyclopedia
Takakia is a genus
of two species of moss
known from western North America
and central and eastern Asia
. The genus is placed as a separate family
, order
and class
among the mosses. It has had a history of uncertain placement, but the discovery of sporophyte
s clearly of the moss-type firmly supports placement with the mosses.
and described by Mitten in 1861. It was originally described simply as a new liverwort
species (Lepidozia
ceratophylla) within an existing genus, and it was thus long overlooked. The discovery of similar odd plants in the mid-20th century by Dr. Takaki 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
plants. Eventually, plants with archegonia
were found, which resembled the archegonia found in mosses. Fertile plants bearing antheridia
and sporophyte
s were first reported in 1993 from the Aleutian Islands, 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 Asia
, Takakia has since been found in Sikkim
(in the Himalayas
), North Borneo
, Taiwan
, and Japan
. In North America
, the genus is found in the Aleutian Islands and British Columbia
. It occurs in a variety of local habitats, from bare rock, to moist humus, and grows at elevations ranging from sea level
to the subalpine
.
s. The plant's Japanese name (nanjamonja-goke) "impossible moss" reflects this. It was believed to have the lowest known chromosome
count (n=4) per cell of any land plant
., but some plants of the small Australian daisy Brachyscome dichromosomatica are now known to have a count of n=2.
From a distance, Takakia looks like a typical layer of moss or green algae on the rock where it grows. On closer inspection, tiny shoots of Takakia grow from a turf of slender, creeping rhizome
s. 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. Both the green shoots and their leaves are very brittle.
Unlike in other bryophyte
s, the egg-producing archegonia
and sperm-producing antheridia
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.
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...
of two species of moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
known from western North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
and central and eastern Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
. The genus is placed as a separate family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
and class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
among the mosses. It has had a history of uncertain placement, but the discovery of 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 clearly of the moss-type firmly supports placement with the mosses.
Discovery
Takakia was discovered in the HimalayasHimalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
and described by Mitten in 1861. It was originally described simply as a new liverwort
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
species (Lepidozia
Lepidozia
Lepidozia is a genus of liverwort in family Lepidoziaceae. It contains the following species :* Lepidozia azorica, Buch & Perss....
ceratophylla) within an existing genus, and it was thus long overlooked. The discovery of similar odd plants in the mid-20th century by Dr. Takaki in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
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
Gametophyte
A 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....
plants. Eventually, plants with archegonia
Archegonium
An archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
were found, which resembled the archegonia found in mosses. Fertile plants bearing antheridia
Antheridium
An antheridium or antherida is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
and 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 were first reported in 1993 from the Aleutian Islands, 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 Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, Takakia has since been found in Sikkim
Sikkim
Sikkim is a landlocked Indian state nestled in the Himalayan mountains...
(in the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
), North Borneo
North Borneo
North Borneo was a British protectorate under the sovereign North Borneo Chartered Company from 1882 to 1946. After the war it became a crown colony of Great Britain from 1946 to 1963, known in this time as British North Borneo. It is located on the northeastern end of the island of Borneo. It is...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
, and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. In North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, the genus is found in the Aleutian Islands and British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
. It occurs in a variety of local habitats, from bare rock, to moist humus, and grows at elevations ranging from sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
to the subalpine
Subalpine
The subalpine zone is the biotic zone immediately below tree line around the world. Species that occur in this zone depend on the location of the zone on the Earth, for example, Snow Gum in Australia, or Subalpine Larch, Mountain Hemlock and Subalpine Fir in western North America.Trees in the...
.
Description
Takakia is not only unusual among mosses, but among all living plantPlant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s. The plant's Japanese name (nanjamonja-goke) "impossible moss" reflects this. It was believed to have the lowest known chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
count (n=4) per cell of any land plant
Embryophyte
The land plants or embryophytes, more formally Embryophyta or Metaphyta, are the most familiar group of plants. They are called 'land plants' because they live primarily in terrestrial habitats, in contrast with the related green algae that are primarily aquatic. The embryophytes include trees,...
., but some plants of the small Australian daisy Brachyscome dichromosomatica are now known to have a count of n=2.
From a distance, Takakia looks like a typical layer of moss or green algae on the rock where it grows. On closer inspection, tiny shoots of Takakia grow from a turf of slender, creeping rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s. 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. Both the green shoots and their leaves are very brittle.
Unlike in other bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s, the egg-producing archegonia
Archegonium
An archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
and sperm-producing antheridia
Antheridium
An antheridium or antherida is a haploid structure or organ producing and containing male gametes . It is present in the gametophyte phase of lower plants like mosses and ferns, and also in the primitive vascular psilotophytes...
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
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...
develops a long stalk ending in an elongated spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
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
family Takakiaceae
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| The classification of Takakia, and its phylogenetic Phylogenetics In biology, phylogenetics is the study of evolutionary relatedness among groups of organisms , which is discovered through molecular sequencing data and morphological data matrices... position among the mosses. |
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External links
- J. R. Spence & W. B. Schofield. 2005. Bryophyte Flora of North America: Takakiaceae