43-642: Zygnematophyceae (or Conjugatophyceae ) is a class of green algae in the paraphylum streptophyte algae, also referred to as Charophyta , consisting of more than 4000 described species. The Zygnematophyceae are the sister clade of the Embryophyta (land plants). Common members of the Zygnematophyceae include the filamentous algae Spirogyra and Mougeotia , as well as desmids , which are microscopic algae characterized by symmetrical and elaborately ornate cells. The body plan of Zygnematophyceae
86-468: A desmid is often divided into two symmetrical compartments separated by a narrow bridge or isthmus, wherein the spherical nucleus is located. Each semi-cell houses a large, often folded chloroplast for photosynthesizing . One or more pyrenoids can be found. These form carbohydrates for energy storage. The cell-wall, of two halves (termed semicells), which, in a few species of Closterium and Penium , are of more than one piece, has two distinct layers,
129-458: A group of microscopic, mostly single-celled algae in the class Zygnematophyceae. Within the desmids, a distinction is typically made between "saccoderm" and "placoderm" desmids. Saccoderm desmids, corresponding to the family Mesotaeniaceae in the order Zygnematales , consist of cells that are unconstricted at the middle, lack median suture lines, and do not have mucilage-secreting pores in the cell wall. Meanwhile, placoderm desmids, corresponding to
172-414: A group of photosynthetic, eukaryotic organisms that include species with haplobiontic and diplobiontic life cycles. The diplobiontic species, such as Ulva , follow a reproductive cycle called alternation of generations in which two multicellular forms, haploid and diploid, alternate, and these may or may not be isomorphic (having the same morphology). In haplobiontic species only the haploid generation,
215-469: A multicellular gametophyte. All land plants have a diplobiontic common ancestor, and diplobiontic forms have also evolved independently within Ulvophyceae more than once (as has also occurred in the red and brown algae). Diplobiontic green algae include isomorphic and heteromorphic forms. In isomorphic algae, the morphology is identical in the haploid and diploid generations. In heteromorphic algae,
258-631: A single cell. The shape of the chloroplast may be star-shaped (in Zygnema ), ribbon-shaped (in Spirogyra ), or elaborately lobed and dissected. In some taxa, particularly Mougeotia , the chloroplast is able to move in response to different light conditions. In the Zygnematophyceae, cell walls are composed of three layers: one outer layer consisting of mucus, a primary wall consisting of microfibrils , and an innermost layer of cellulosic microfibrils . Some species shed their primary wall and retain only
301-590: A single family Desmidiaceae , most classifications recognize three to five families, usually within their own order, Desmidiales. The Desmidiales comprise around 40 genera and 5,000 to 6,000 species , found mostly but not exclusively in fresh water . In general, desmids prefer acidic waters (pH between 4.8 and 7.0), so many species may be found in the fissures between patches of sphagnum moss in marshes. As desmids are sensitive to changes in their environments, they are useful as bioindicators for water and habitat quality. The term "desmid" typically refers to
344-468: Is a unicellular, isogamous charophycean alga group that is the closest unicellular relative to land plants. Heterothallic strains of different mating type can conjugate to form zygospores . Sex pheromones termed protoplast-release inducing proteins (glycopolypeptides) produced by mating-type (-) and mating-type (+) cells facilitate this process. The green algae, including the characean algae, have served as model experimental organisms to understand
387-461: Is simple, and the group appears to have gone through a secondary loss of morphological complexity. The most basal members are unicellular, but filamentous species have evolved at least five times, and a few species form colonies. Each cell contains a single nucleus . The chloroplasts of the Zygnematophyceae are large, typically axile but sometimes parietally located, and contain one or several pyrenoids . One or several chloroplasts may be present in
430-433: The (green) plants (with chloroplasts ) the red algae (with rhodoplasts) and the glaucophytes (with muroplasts). Green algae are often classified with their embryophyte descendants in the green plant clade Viridiplantae (or Chlorobionta ). Viridiplantae, together with red algae and glaucophyte algae, form the supergroup Primoplantae, also known as Archaeplastida or Plantae sensu lato . The ancestral green alga
473-584: The Closterium peracerosum–strigosum–littorale complex. Furthermore, the gene models of Mesotaenium endlicherianum have been updated. Green algae The green algae ( sg. : 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 ( Embryophytes ) have emerged deep in
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#1732786914199516-497: The gametophyte is multicellular. The fertilized egg cell, the diploid zygote , undergoes meiosis , giving rise to haploid cells which will become new gametophytes. The diplobiontic forms, which evolved from haplobiontic ancestors, have both a multicellular haploid generation and a multicellular diploid generation. Here the zygote divides repeatedly by mitosis and grows into a multicellular diploid sporophyte . The sporophyte produces haploid spores by meiosis that germinate to produce
559-507: The supralittoral zone , is terrestrial and can in the Antarctic form large carpets on humid soil, especially near bird colonies. Green algae have chloroplasts that contain chlorophyll a and b , giving them a bright green colour, as well as the accessory pigments beta carotene (red-orange) and xanthophylls (yellow) in stacked thylakoids . The cell walls of green algae usually contain cellulose , and they store carbohydrate in
602-1094: The Charophyte alga as a sister of the Zygnematophyceae . Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae . The green algae include unicellular and colonial flagellates , most with two flagella per cell, as well as various colonial, coccoid (spherical), and filamentous forms, and macroscopic, multicellular seaweeds . There are about 22,000 species of green algae, many of which live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds. A few other organisms rely on green algae to conduct photosynthesis for them. The chloroplasts in dinoflagellates of
645-723: The Mesostigmatophyceae, Chlorokybophyceae and spirotaenia are only more conventionally basal Streptophytes. The algae of this paraphyletic group "Charophyta" were previously included in Chlorophyta, so green algae and Chlorophyta in this definition were synonyms. As the green algae clades get further resolved, the embryophytes, which are a deep charophyte branch, are included in " algae ", "green algae" and " Charophytes ", or these terms are replaced by cladistic terminology such as Archaeplastida , Plantae / Viridiplantae , and streptophytes , respectively. Green algae are
688-1146: The Zygnematales were found to be paraphyletic with respect to the Desmidiales, and so it was split up. As of 2023, five orders and two subclasses are recognized: the Spirogloeales in Spirogloeophycidae, and the Serritaeniales, the Zygnematales , the Spirogyrales, and the Desmidiales in Zygnematophycidae. Class Zygnematophyceae A phylogeny of the families of Zygnematophyceae is presented below: Spirogloeaceae Serritaeniaceae Zygnemataceae Mesotaeniaceae Spirogyraceae Gonatozygaceae Closteriaceae Peniaceae Desmidiaceae Members of
731-548: The Zygnematophyceae are common in nearly all freshwater habitats, particularly filamentous genera such as Spirogyra and Mougeotia . Some Spirogyra species can tolerate disturbed habitats. On the other hand, desmids (the Desmidiales) often prefer bogs, peatlands, and lakes. Vegetative cells of the Zygnematophyceae are fragile and usually not preserved, but the zygospores are resistant to decay and can become fossilized. The Zygnematophyceae have been recorded from at least
774-619: The Zygnematophyceae takes place through a process called conjugation . Unusually, the gametes lack flagella , and they also lack centrioles which suggest that flagella were not secondarily lost. This lack of flagella sets the Zygnematophyceae apart from nearly all groups of algae, except for red algae and cyanobacteria (also known as blue-green algae, if they are classified as such). The gametes are scarcely differentiated from vegetative cells. In conjugation, cells or filaments of opposite sex line up, and tubes form between corresponding cells. The male cells then become amoeboid and crawl across
817-545: The basis for their classification. The largest among them may be visible to the unaided eye. Desmids possess characteristic crystals of barium sulphate at either end of the cell which exhibit continuous Brownian motion . The function of these crystals is completely unknown. Many desmids also secrete translucent, gelatinous mucilage from pores in the cell wall that acts as a protecting agent. These pores are either, as in Micrasterias , uniformly distributed across
860-606: The canal passes. This is termed the pore-organ. The canals are no doubt in all cases occupied by threads of mucilage in process of excretion. At the inner surface of the wall they terminate in lens- or button-shaped swellings, while from the outer end of the pore-organ there sometimes arise delicate radiating or club-shaped masses of mucilage through which the canal passes and which appear to be more or less permanent in character. In most cases, however, these are absent or only represented by small perforated buttons. Desmids most commonly reproduce by asexual fission . During cell division,
903-456: The cell-wall but always appear to be absent in the region of the isthmus, or, in highly ornamented forms, as many genera of Cosmarium , grouped symmetrically around the bases of the spines, warts and so on with which the cell is provided. In the inner layer of the wall the pore is a simple canal, but in the outer, except in Closterium , the canal is surrounded by a specially differentiated cylindrical zone, not composed of cellulose, through which
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#1732786914199946-413: The class Chlorophyceae undergo closed mitosis in the most common form of cell division among the green algae, which occurs via a phycoplast . By contrast, charophyte green algae and land plants (embryophytes) undergo open mitosis without centrioles . Instead, a 'raft' of microtubules, the phragmoplast , is formed from the mitotic spindle and cell division involves the use of this phragmoplast in
989-605: The families and genera in the Desmidiales: The family Gonatozygaceae is sometimes included within the Peniaceae , reducing the number of families from four to three. A fifth family Mesotaeniaceae was formerly included in the Desmidiales, but analysis of cell wall structure and DNA sequences show that the group is more closely related to the Zygnemataceae , and so is now placed together with that family in
1032-410: The female, or sometimes both cells crawl into the connecting tube. The cells then meet and fuse to form a zygote , which later undergoes meiosis to produce new cells or filaments. As in land plants, only the female passes its chloroplasts on to the offspring. The Zygnematophyceae is monophyletic . Traditionally, it has been known to contain two orders, the Zygnematales and Desmidiales . However,
1075-427: The form of starch . All green algae have mitochondria with flat cristae . When present, paired flagella are used to move the cell. They are anchored by a cross-shaped system of microtubules and fibrous strands. Flagella are only present in the motile male gametes of charophytes bryophytes, pteridophytes, cycads and Ginkgo , but are absent from the gametes of Pinophyta and flowering plants . Members of
1118-435: The fungal species that partner in lichens cannot live on their own, while the algal species is often found living in nature without the fungus. Trentepohlia is a filamentous green alga that can live independently on humid soil, rocks or tree bark or form the photosymbiont in lichens of the family Graphidaceae . Also the macroalga Prasiola calophylla (Trebouxiophyceae) is terrestrial, and Prasiola crispa , which live in
1161-584: The genus Lepidodinium , euglenids and chlorarachniophytes were acquired from ingested endosymbiont green algae, and in the latter retain a nucleomorph (vestigial nucleus). Green algae are also found symbiotically in the ciliate Paramecium , and in Hydra viridissima and in flatworms . Some species of green algae, particularly of genera Trebouxia of the class Trebouxiophyceae and Trentepohlia (class Ulvophyceae ), can be found in symbiotic associations with fungi to form lichens . In general
1204-402: The heat of late summer. As their environment dries out, asexual V. carteri quickly die. However, they are able to escape death by switching, shortly before drying is complete, to the sexual phase of their life cycle that leads to production of dormant desiccation-resistant zygotes . Sexual development is initiated by a glycoprotein pheromone (Hallmann et al., 1998). This pheromone is one of
1247-525: The inner composed mainly of cellulose, the outer is stronger and thicker, often furnished with spines, granules, warts et cetera. It is made up of a base of cellulose impregnated with other substances including iron compounds, which are especially prominent in some species of Closterium and Penium and is not soluble in an ammoniacal solution of copper oxide. Desmids assume a variety of highly symmetrical and generally attractive shapes, among those elongated, star-shaped and rotund configurations, which provide
1290-521: The innermost layer. The cell wall may be variously decorated with striations, granules, or spines. In the Desmidiales, there are pores in the cell wall which allow the cell to extrude a layer of mucilage for protection. Several Zygnematophyceae contain genes involved in protection from desiccation that appear to have been derived by horizontal gene transfer from bacteria; the genes are found in plants, Zygnematophyceae, and bacteria , but no other organisms. The genes may have helped to enable plants to make
1333-402: The land plants ( Embryophyta ) emerged. Desmids consist of single-celled (sometimes filamentous or colonial) microscopic green algae. Because desmids are highly symmetrical, attractive, and come in a diversity of forms, they are popular subjects for microscopists , both amateur and professional. The desmids belong to the class Zygnematophyceae . Although they are sometimes grouped together as
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1376-461: The light microscope. This process is called conjugation and occurs for example in Spirogyra . Sex pheromone production is likely a common feature of green algae, although only studied in detail in a few model organisms. Volvox is a genus of chlorophytes . Different species form spherical colonies of up to 50,000 cells. One well-studied species, Volvox carteri (2,000 – 6,000 cells) occupies temporary pools of water that tend to dry out in
1419-490: The mechanisms of the ionic and water permeability of membranes, osmoregulation , turgor regulation, salt tolerance , cytoplasmic streaming , and the generation of action potentials . Desmidiales Closteriaceae Desmidiaceae Gonatozygaceae Peniaceae Desmidiales , commonly called the desmids ( Gr. desmos , bond or chain), are an order in the Charophyta , a division of green algae in which
1462-475: The middle Devonian period, and before the Carboniferous period, all the major groups had diverged. Fossils of zygospores are indicators of warming spring conditions and shallow, stagnant mesotrophic habitats. The first genomes published for Zygnematophyceae were Mesotaenium endlicherianum and Spirogloea muscicola . Since then, genomes have been published on Penium margaritaceum , Zygnema spp., and
1505-587: The morphology and size are different in the gametophyte and sporophyte. Reproduction varies from fusion of identical cells ( isogamy ) to fertilization of a large non-motile cell by a smaller motile one ( oogamy ). However, these traits show some variation, most notably among the basal green algae called prasinophytes . Haploid algal cells (containing only one copy of their DNA) can fuse with other haploid cells to form diploid zygotes. When filamentous algae do this, they form bridges between cells, and leave empty cell walls behind that can be easily distinguished under
1548-417: The most potent known biological effector molecules. It can trigger sexual development at concentrations as low as 10 M. Kirk and Kirk showed that sex-inducing pheromone production can be triggered experimentally in somatic cells by heat shock . Thus heat shock may be a condition that ordinarily triggers sex-inducing pheromone in nature. The Closterium peracerosum-strigosum-littorale (C. psl) complex
1591-755: The order Zygnematales . However, the Zygnemataceae may have emerged in the Mesotaeniaceae . Desmids are found in freshwater habitats all over the world, but strongly prefer bogs, mires, and other nutrient-poor wetlands. They generally have strict ecological requirements: most species prefer waters with low amounts of dissolved calcium and magnesium, low salinity levels, and somewhat acidic pH. In waters with higher amounts of nutrients, desmids rapidly become outcompeted . Desmid species are generally found attached to aquatic vegetation, such as Utricularia , or tychoplanktonic ; that is, free-floating in
1634-530: The order Desmidiales, consist of cells with two symmetrical halves, and mucilage-secreting pores in the cell wall. Here, the term "desmids" and "placoderm desmids" will be used interchangeably to refer to the Desmidiales. The structure of these algae is unicellular , and lacks flagella . Although most desmid species are unicellular, some genera form chains of cells, called filaments. A few genera form non-filamentous colonies, with individual cells connected by threads or remnants of parent cell walls. The cell of
1677-413: The production of a cell plate . Photosynthetic eukaryotes originated following a primary endosymbiotic event, where a heterotrophic eukaryotic cell engulfed a photosynthetic cyanobacterium -like prokaryote that became stably integrated and eventually evolved into a membrane-bound organelle : the plastid . This primary endosymbiosis event gave rise to three autotrophic clades with primary plastids:
1720-597: The transition to life on land. A new subclass called Spirogloeophycidae, represented by the species Spirogloea muscicola , was established after the unicellular subaerial algae, resembling a "gelatinous blob", was rediscovered on a rock close to a river bank near Cologne in 2006, after first being discovered in France in 1845. The Zygnematophyceae are able to reproduce both asexually and sexually. Asexual reproduction takes place via fragmentation, cell division , akinete formation, or parthenospores. Sexual reproduction in
1763-470: The two halves of a cell separate, and each half develops into a new cell. After division, a cell may be asymmetric since the recently formed half is smaller than the original half. In adverse conditions, desmids may reproduce sexually through a process of conjugation , which are also found among other closely related taxa in the Zygnematophyceae . Sexual reproduction is rare, and many species have never been observed sexually reproducing. Classification of
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1806-477: The water column after being disturbed. Although the Desmidiales are cosmopolitan, a number of species appear to be restricted to continents or biogeographical realms ; this is likely because desmids have strict ecological requirements and do not produce resting spores , making successful dispersal less likely. Therefore, they can be grouped into several regions each with their own characteristic desmid floras. The Indo-Malayan to North Australian realm, for example,
1849-963: Was a unicellular flagellate. The Viridiplantae diverged into two clades. The Chlorophyta include the early diverging prasinophyte lineages and the core Chlorophyta, which contain the majority of described species of green algae. The Streptophyta include charophytes and land plants. Below is a consensus reconstruction of green algal relationships, mainly based on molecular data. Palmophyllophyceae (prasinophyte clade VI) Prasinodermophyceae Ulvophyceae Chlorophyceae Trebouxiophyceae Chlorodendrophyceae Pedinophyceae Prasinophytes Clade VIIA Prasinophytes Clade VIIC Pycnococcaceae Nephroselmidophyceae Mamiellophyceae Pyramimonadales Mesostigmatophyceae Spirotaenia Chlorokybophyceae Streptofilum Klebsormidiophyceae Charophyceae Coleochaetophyceae Zygnematophyceae Mesotaeniaceae s.s. Embryophyta (land plants) The basal character of
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