Charophyta () is a
paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
group of
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
green algae
The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...
, called charophytes (), sometimes treated as a
division,
yet also as a
superdivision.
The terrestrial plants, the
Embryophyta emerged deep within Charophyta, possibly from terrestrial unicellular charophytes, with the class
Zygnematophyceae as a
sister group
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
.
With the Embryophyta now
cladistically placed in the Charophyta, it is a synonym of
Streptophyta
Streptophyta (), informally the streptophytes (, from the Greek ''strepto'' 'twisted', for the morphology of the sperm of some members), is a clade of plants. The composition of the clade varies considerably between authors, but the definition e ...
.
The sister group of the charophytes are the
Chlorophyta
Chlorophyta is a division of green algae informally called chlorophytes.
Description
Chlorophytes are eukaryotic organisms composed of cells with a variety of coverings or walls, and usually a single green chloroplast in each cell. They are ...
. In some charophyte groups, such as the
Zygnematophyceae or conjugating green algae,
flagella
A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
are absent and sexual reproduction does not involve free-swimming flagellate sperm. Flagellate sperm, however, are found in
stoneworts (
Charales
Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Depending on the treatment of the genus '' Nitellopsis'', living (extant) species are placed into either one family ( ...
) and
Coleochaetales, orders of parenchymatous charophytes that are the closest relatives of the land plants, where flagellate sperm are also present in all except the
conifers
Conifers () are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All e ...
and
flowering plants
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
.
Fossil stoneworts of early
Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
age that are similar to those of the present day have been described from the
Rhynie chert
The Rhynie chert is a Lower Devonian Sedimentary rock, sedimentary deposit exhibiting extraordinary fossil detail or completeness (a Lagerstätte). It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield ...
of Scotland.
[ Somewhat different charophytes have also been collected from the Late Devonian (Famennian) Waterloo Farm lagerstätte of South Africa. These include two species each of '']Octochara
''Octochara'' is a genus of fossil charophyte (aquatic green alga) from the Famennian (Late Devonian). It is one of two genera of charophyte described from the Waterloo Farm lagerstätte in southern Africa. It and ''Hexachara'', from the same loc ...
'' and '' Hexachara'', which are the oldest fossils of Charophyte axes bearing in situ oogonia
An oogonium (: oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes.
In the mammalian fetus
Oogonia are formed in lar ...
.
The name comes from the genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
'' Chara'', but the finding that the Embryophyta actually emerged in them has ''not'' resulted in a much more restricted meaning of the Charophyta, namely to a much smaller side branch. This more restricted group corresponds to the Charophyceae.
Description
The Zygnematophyceae, formerly known as the Conjugatophyceae, generally possess two fairly elaborate chloroplast
A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
s in each cell, rather than many discoid ones. They reproduce asexually by the development of a septum between the two cell-halves or semi-cells (in unicellular forms, each daughter-cell develops the other semi-cell afresh) and sexually by conjugation, or the fusion of the entire cell-contents of the two conjugating cells. The saccoderm desmids and the placoderm or true desmids, unicellular or filamentous members of the Zygnematophyceae, are dominant in non-calcareous, acid waters of oligotrophic or primitive lake
A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...
s (e.g. Wastwater), or in lochans, tarns and bogs, as in the West of Scotland, Eire, parts of Wales and of the Lake District.
''Klebsormidium
''Klebsormidium'' is a genus of filamentous charophyte green algae comprising 20 species. The name was proposed in 1972 to resolve confusion in application and status of ''Hormidium'' and was given for the German botanist Georg Klebs, Georg Albre ...
'', the type of the Klebsormidiophyceae, is a simple filamentous form with circular, plate-like chloroplasts, reproducing by fragmentation, by dorsiventral, biciliate swarmers and, according to Wille, a twentieth-century algologist, by aplanospores. Sexual reproduction is simple and isogamous (the male and female gametes are outwardly indistinguishable).[
The ]Charales
Charales is an order of freshwater green algae in the division Charophyta, class Charophyceae, commonly known as stoneworts. Depending on the treatment of the genus '' Nitellopsis'', living (extant) species are placed into either one family ( ...
(Charophyceae), or stoneworts, are freshwater and brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...
algae with slender green or grey stems; the grey colour of many species results from the deposition of lime on the walls, masking the green colour of the chlorophyll. The main stems are slender and branch occasionally. Lateral branchlet
A branch, also called a ramus in botany, is a stem that grows off from another stem, or when structures like veins in leaves are divided into smaller veins.
History and etymology
In Old English, there are numerous words for branch, includ ...
s occur in whorls at regular intervals up the stem, they are attached by rhizoids to the substrate.[Bryant 2007, J. The Stoneworts (Chlorophyta, Charales) in Guiry, M.D., John, D.M., Rindi, F. and McCarthy, T.K (Ed) ''New Survey of Clare Island Volume 6: The Freshwater and Terrestrial Algae''. Royal Irish Academy. ] The reproductive organs consist of antheridia and oogonia
An oogonium (: oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes.
In the mammalian fetus
Oogonia are formed in lar ...
, though the structures of these organs differ considerably from the corresponding organs in other algae. As a result of fertilization, a protonema is formed, from which the sexually reproducing algae develops.
A new terrestrial genus found in sandy soil in the Czech Republic
The Czech Republic, also known as Czechia, and historically known as Bohemia, is a landlocked country in Central Europe. The country is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the south ...
, ''Streptofilum'', may belong in its own class due its unique phylogenetic position. A cell wall
A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...
is absent, instead the cell membrane
The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
consists of many layers of specific scales. It is a short, filamentous and unbranched algae surrounded by a mucilaginous sheath, which often disintegrates to diads and unicells.
Reproduction
The cells in Charophyta algae are all haploid
Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...
, except during sexual reproduction, where a diploid unicellular zygote is produced. The zygote becomes four new haploid cells through meiosis, which will develop into new algae. In multicellular forms these haploid cells will grow into a 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 se ...
. In embryophytes (land plants) the zygote will instead give rise to a multicellular sporophyte
A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...
.
Except from land plants, retention of the zygote is only known from some species in one group of green algae; the coleochaetes. In these species the zygote is corticated by a layer of sterile gametophytic cells. Another similarity is the presence of sporopollenin in the inner wall of the zygote. In at least one species, it receives nourishment from the gametophyte through placental transfer cells.
Classification
Charophyta are complex green algae that form a sister group to the Chlorophyta
Chlorophyta is a division of green algae informally called chlorophytes.
Description
Chlorophytes are eukaryotic organisms composed of cells with a variety of coverings or walls, and usually a single green chloroplast in each cell. They are ...
and within which the Embryophyta emerged. The chlorophyte
Chlorophyta is a division (botany), division of green algae informally called chlorophytes.
Description
Chlorophytes are eukaryotic organisms composed of cells with a variety of coverings or walls, and usually a single green chloroplast in ea ...
and charophyte green algae and the embryophytes or land plants form a clade called the green plants or Viridiplantae
Viridiplantae (; kingdom Plantae '' sensu stricto'') is a clade of around 450,000–500,000 species of eukaryotic organisms, most of which obtain their energy by photosynthesis. The green plants are chloroplast-bearing autotrophs that play impo ...
, that is united among other things by the absence of phycobilin
Phycobilins (from Greek: '' (phykos)'' meaning "alga", and from Latin: ''bilis'' meaning "bile") are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads (though not in green a ...
s, the presence of chlorophyll a and chlorophyll b
}
Chlorophyll ''b'' is a form of chlorophyll. Chlorophyll ''b'' helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll ''a'' in polar solvents because of its carbonyl group. Its color is green, and it primarily ...
, cellulose in the cell wall and the use of starch
Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...
, stored in the plastids, as a storage polysaccharide. The charophytes and embryophytes share several traits that distinguish them from the chlorophytes, such as the presence of certain enzymes (class I aldolase, Cu/Zn superoxide dismutase
Superoxide dismutase (SOD, ) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide () anion radical into normal molecular oxygen (O2) and hydrogen peroxide (). Superoxide is produced as a by-product of oxy ...
, glycolate oxidase, flagellar peroxidase
Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides, and should not be confused with other ...
), lateral flagella (when present), and, in many species, the use of phragmoplasts in mitosis
Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...
. Thus Charophyta and Embryophyta together form the clade Streptophyta
Streptophyta (), informally the streptophytes (, from the Greek ''strepto'' 'twisted', for the morphology of the sperm of some members), is a clade of plants. The composition of the clade varies considerably between authors, but the definition e ...
, excluding the Chlorophyta.
Charophytes such as ''Palaeonitella cranii'' and possibly the yet unassigned '' Parka decipiens'' are present in the fossil record of the Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
. ''Palaeonitella'' differed little from some present-day stoneworts.
Cladogram
There is an emerging consensus on green algal relationships, mainly based on molecular data. The Mesostigmatophyceae (including ''Spirotaenia'', and Chlorokybophyceae) are at the base of charophytes (streptophytes). The cladograms below show consensus phylogenetic relationships based on plastid genomes and a new proposal for a third phylum of green plants based on analysis of nuclear genomes.
Mesostigmatophyceae s.l. in the cladograms corresponds to a clade of a narrower circumscription, Mesostigmatophyceae s.s., and a separate class Chlorokybophyceae, as used by AlgaeBase
AlgaeBase is a global species database of information on all groups of algae, both seaweed, marine and freshwater algae, freshwater, as well as sea-grass.
History
AlgaeBase began in March 1996, founded by Michael D. Guiry, Michael Guiry. Text ...
.
The Mesostigmatophyceae are not filamentous, but the other basal charophytes (streptophytes) are.
References
External links
*
{{Life on Earth
Green algae phyla
Algae phyla