micrasterias micrasterias micrasterias is a unicellular green alga of the order desmidiales. its species vary in size reaching up to hundreds of microns. micrasterias micrasterias furcata scientific classification (unranked): viridiplantae (unranked): charophyta class: zygnematophyceae order: desmidiales family: desmidiaceae genus: micrasteriasc.agardh ex ralfs type species micrasterias furcatac.agardh ex ralfs species see text. micrasterias displays a bilateral symmetry, with two mirror image semi-cells joined by a narrow isthmus containing the nucleus of the organism. this dual semi-cell structure is unique to the group of green algae to which micrasterias belongs. each semi-cell contains a single large chloroplast, the site of photosynthesis for micrasterias. chloroplasts within micrasterias contain chlorophyll a and chlorophyll b and the enzymes required for photosynthesis. the sugar created is used to provide energy for the organism or, if not used, taken up by many small round pyrenoids which are embedded in the chloroplast. they convert the sugar to a starch for storage. micrasterias can produce both asexually and sexually. asexual reproduction occurs via mitosis. when this occurs the genetic material of micrasterias is duplicated and two small semi-cells grow between the original semi-cells, gradually increasing in size. sexual reproduction occurs through a process called conjugation whereby two organisms come together and fuse their haploid cells to form a diploid zygote. this zygote typically forms a thick protective wall which can allow the organism to remain dormant for many months to survive cold winters and long droughts. when adequate conditions resume, the zygospore will germinate, undergo meiosis, and produce new haploid algal cells. description micrasterias species are symmetrical and generally consist of two flattened, identical portions called semicells that are almost entirely filled with chloroplasts, with a nucleus that lies at the center where the two semicells are joined together. the gaps between the two semicells are joined by an isthmus. each semicell is further divided into a polar lobe and two lateral lobes. these lobes can be further subdivided up to the fourth order. some species, such as micrasterias laticeps, have a very different morphology, with unbranched lobes. except for a single filament-forming species, micrasterias foliacea, it is found as single cells. as is common in the green algae, the chloroplasts of micrasterias contain pyrenoids. two species of micrasterias have different morphologies to species traditionally placed in this genus, but molecular phylogenetic analyses demonstrate that they are embedded within micrasterias. micrasterias ralfsii (formerly classified as cosmarium ralfsii) has no lobes, and the cells are smoothly ellipsoidal in outline. micrasterias dickiei (formerly classified as staurodesmus dickiei) is triradiate in polar view instead of flattened, and has three spines on each semicell. similar genera micrasterias is generally easy to identify due to its shape and typically large size. the genus pseudomicrasterias has been split off from the genus micrasterias, and as of 2023, contains 2 species, formerly known as micrasterias arcuata. they have a similar morphology to the simpler species of micrasterias, but molecular phylogenetic analyses show that they are not related. the genus prescottiella contains a single species, prescottiella sudanensis, formerly known as micrasterias sudanensis. it is distinguished from micrasterias in that its semicells are not identical, making the cell asymmetrical along one axis; the spines of one semicell curve towards the isthmus, while the spines of the other semicell curve away. species accepted species micrasterias rotata micrasterias comprises the following species: micrasterias abrupta west & g.s.west micrasterias adscendens nordstedt micrasterias africana (f.e.fritsch & f.rich) coesel & van geest micrasterias alata wallich micrasterias ambadiensis (grönblad & a.m.scott) kurt föster micrasterias americana ehrenberg ex ralfs micrasterias anomala w.b.turner micrasterias apiculata meneghini ex ralfs micrasterias archeri coesel & m.dingley micrasterias bangladeshensis a.k.islam & haroon micrasterias bewsii fritsch & m.f.rich micrasterias bicoronata a.kenins micrasterias borgei willi krieger micrasterias bourrellyana j.a.rino micrasterias brachyptera lundell micrasterias ceratofera joshua micrasterias compereana neustupa, st'astný & skaloud micrasterias conferta lundell micrasterias croasdaleana c.e.m.bicudo & l.sormus micrasterias crux-africana f.j.cohn micrasterias crux-melitensis ralfs micrasterias cunningtonii g.s.west micrasterias decemdentata (nägeli) w.archer micrasterias denboeri coesel & van geest micrasterias denticulata brébisson ex ralfs micrasterias depauperata nordstedt micrasterias dickiei (ralfs) škaloud et al. micrasterias divisa willi krieger micrasterias echinata p.e.brandham micrasterias elegans (w.west & g.s.west) coesel & van geest micrasterias elongata (schmidle) coesel & van geest micrasterias euastriellopsis bharati micrasterias excavata (nordstedt) c.e.m.bicudo & l.sormus micrasterias fimbriata ralfs micrasterias foersteri thomasson micrasterias foliacea bailey ex ralfs micrasterias furcata c.agardh ex ralfs micrasterias groenewaldii claassen micrasterias hardyi g.s.west micrasterias hieronymusii schmidle micrasterias horrida c.e.taft micrasterias incisa ralfs micrasterias inflata c.bernard micrasterias integra nordstedt micrasterias jejuensis h.s.kim micrasterias jenneri ralfs micrasterias johnsonii west & g.s.west micrasterias khasiae w.b.turner micrasterias koreana h.s.kim micrasterias laticeps nordstedt micrasterias lebrunii oye micrasterias ledouxii a.m.scott & croasdale micrasterias lundii bourrelly micrasterias lux joshua micrasterias madagascariensis coesel micrasterias mahabuleshwarensis j.hobson micrasterias moebii (o.borge) west & g.s.west micrasterias muricata bailey ex ralfs micrasterias nordstedtiana wolle micrasterias nordstedtii thomasson micrasterias nylstromica claassen micrasterias oscitans ralfs micrasterias papillifera brébisson ex ralfs micrasterias pinnatifida ralfs micrasterias piquata r.k.salisbury micrasterias prescottiana c.e.m.bicudo & l.sormus micrasterias pseudotorreyi wolle micrasterias quadridentata (nordstedt) grönblad micrasterias quadriverrucosa (thomasson) c.e.m.bicudo & l.sormus micrasterias radians w.b.turner micrasterias radiosa ralfs micrasterias ralfsii (brébisson ex ralfs) škaloud et al. micrasterias rotata ralfs micrasterias sanctipaulensis c.e.m.bicudo & l.sormus micrasterias schmidleana coesel & van geest micrasterias schweickerdtii m.i.claassen micrasterias schweinfurthii cohn micrasterias semiradiata brébisson ex kützing micrasterias sexpinata (irénée-marie & hilliard) h.croasdale & g.w.prescott micrasterias simplex børgesen micrasterias spinosa h.s.kim micrasterias stauromorpha w.b.turner micrasterias subaequalis grönblad micrasterias subdenticulata (nordstedt) willi krieger micrasterias subincisa willi krieger micrasterias suboblonga nordstedt micrasterias subtruncata a.i.lobik micrasterias tetraptera west & g.s.west micrasterias thomasiana w.archer micrasterias torreyi bailey micrasterias triangularis wolle micrasterias tropica nordstedt micrasterias truncata brébisson ex ralfs micrasterias verrucosa bisset micrasterias zeylanica f.e.fritsch species names with uncertain taxonomic status the status of the following species is unresolved: micrasterias aculeata m.rostock micrasterias berganii h.v.hauge micrasterias bicaudata (a.k.h.braun ex kützing) kuntze micrasterias bioctonaria g.rabenhorst micrasterias boryana (p.j.f.turpin) ehrenberg micrasterias boryi kützing micrasterias braunii (c.w.nägeli ex kützing) kuntze micrasterias comperei r.s.ganem & p.a.c.senna micrasterias complecta c.g.t.preuss micrasterias convoluta (a.k.j.corda) kuntze micrasterias cordae a.braun micrasterias coronula ehrenberg micrasterias cruciata kützing micrasterias crucigenia kützing micrasterias decemdentatum (c.w.nägeli) w.archer micrasterias denticula istvanfy micrasterias duplex (meyen) kützing micrasterias ecornis ehrenberg micrasterias eichleri schmidle micrasterias enneactis ehrenberg micrasterias extendens w.b.turner micrasterias falcata corda micrasterias floridensis r.k.salisbury micrasterias galeata borge micrasterias ghibellina meneghini micrasterias granulata h.c.wood micrasterias halis raciborski micrasterias hamata (wolle) f.c.e.børgesen micrasterias heliactis kützing micrasterias heptactis ehrenberg micrasterias hermanniana reinsch micrasterias hexactis ehrenberg micrasterias hexagona g.w.grant micrasterias hexagonalis f.steinecke micrasterias kangofurinensis n.woodhead & r.d.tweed micrasterias lacerata kützing micrasterias margaritifera (p.j.f.turpin) l.a.brébisson & p.godet micrasterias mbugensis e.m.lind micrasterias melitensis g.g.a.meneghini micrasterias mohii (borge) authority unknown micrasterias multifida wolle micrasterias napoleonis (p.j.f.turpin) kützing micrasterias nordstetiana wolle micrasterias oblonga ehrenberg micrasterias ornamentalis o.borge micrasterias paradoxa kützing micrasterias platyptera w.b.turner micrasterias polonica (b.eichler & r.gutwinski) west & g.s.west micrasterias polycyclia g.rabenhorst micrasterias pseudofurcata wolle micrasterias quadragies-cuspidata (corda) ralfs micrasterias renicarpa (turpin) kützing micrasterias ricciaeformis c.agardh micrasterias robusta west & g.s.west micrasterias rosula kützing micrasterias selenaea kützing micrasterias senaria ehrenberg micrasterias simplex (meyen) kützing micrasterias simplex wolle micrasterias simplex kurt förster & f.eckert micrasterias sinuata l.a.brébisson micrasterias siolii a.m.scott & croasdale micrasterias sphaerastrum kützing micrasterias staurastrum kützing micrasterias subfimbriata wolle micrasterias sublagoensis kurt förster & f.eckert micrasterias tetracera kützing micrasterias tricera kützing micrasterias tricyclia ehrenberg micrasterias trigemina e.h.p.a.haeckel micrasterias upsaliensis (cleve) w.archer phylogenetics modern molecular phylogenetics suggest the following relationships (not all accepted species are included): micrasterias clade a a1 micrasterias truncata micrasterias ralfsii micrasterias semiradiata a2 micrasterias decemdentata micrasterias laticeps a3 micrasterias zeylanica micrasterias truncata var. pusilla a4 micrasterias furcata micrasterias pinnatifida micrasterias dickiei a5 micrasterias ceratofera micrasterias crux-melitensis pro parte micrasterias radians var. bogoriensis a6 micrasterias crux-melitensis pro parte micrasterias radians var. evoluta clade b micrasterias anomala micrasterias apiculata clade c micrasterias brachyptera micrasterias fimbriata micrasterias rotata micrasterias doveri clade d micrasterias thomasiana micrasterias denticulata micrasterias jenneri clade e triploceras clade f micrasterias tropica clade g micrasterias foliacea micrasterias radiosa var. swainei micrasterias tetraptera micrasterias conferta micrasterias radiosa var. radiosa micrasterias novae-terrae micrasterias papillifera clade h micrasterias hardyi micrasterias americana micrasterias mahabuleshwarensis micrasterias muricata staurastrum (outgroup) even though triploceras was recovered as embedded within micrasterias, there was low statistical support for this placement, so it remains a separate genus. habitat and distribution as with other desmids, micrasterias grows in freshwater habitats. it prefers oligotrophic to mesotrophic lakes and bogs, often associated with aquatic plants. freshwater microalgae, along with other microscopic organisms, are often presumed to be cosmopolitan in distribution (see the baas becking hypothesis). however, many desmids are an exception to this, likely because of their high morphological complexity allowing for easier identification, and the fact that they mostly do not form resting spores that would allow for wider dispersal. in particular, a number of micrasterias species are restricted to certain biogeographical realms or continents. for example, micrasterias muricata appears to be endemic to north america, while micrasterias ceratofera is restricted to southeast asia and northern australia.