{{Short description|Genus of algae}} {{Automatic taxobox | taxon = Eremosphaera | authority = De Bary, 1858 | subdivision_ranks = Species | type_species = ''Eremosphaera viridis'' | type_species_authority = De Bary<ref name=AlgaeBase>{{AlgaeBase genus|id=43432|name=Eremosphaera|access-date=2025-01-31}}</ref> | image = Eremosphaera viridis.jpg | subdivision = * ''Eremosphaera antillana'' * ''Eremosphaera eremosphaeria'' * ''Eremosphaera gigas'' * ''Eremosphaera minor'' * ''Eremosphaera oocystoides'' * ''Eremosphaera tanganyikae'' * ''Eremosphaera viridis'' * ''Eremosphaera yanshanensis'' }}
'''''Eremosphaera''''' is a genus of green algae in the family Oocystaceae.<ref>See the NCBI [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=163306 webpage on Eremosphaera]. Data extracted from the {{cite web | url=https://ftp.ncbi.nih.gov/pub/taxonomy/ | title=NCBI taxonomy resources | publisher=National Center for Biotechnology Information | access-date=2007-03-19}}</ref> It was first described by Heinrich Anton de Bary in 1858, who thought it was a desmid. Since then, many authors have debated its classification,<ref>{{cite journal|doi=10.1086/328166 |title=New or Little Known Unicellular Algae. II. Eremosphaera Viridis and Excentrosphaera |date=1901 |last1=Moore |first1=George Thomas |journal=Botanical Gazette |volume=32 |issue=5 |pages=309–324 |url=https://www.biodiversitylibrary.org/part/223105 }}</ref> until its modern placement in the family Oocystaceae.<ref name=AlgaeBase/>
''Eremosphaera'' is widely distributed in freshwater habitats around the world.<ref name=AlgaeBase/> Most species of ''Eremosphaera'', including the type species ''E. viridis'' are associated with ''Sphagnum'' bogs, which are characteristically acidic<ref name=Matthews>{{cite journal | date = 2016 | last1=Matthews | first1=Robin A. | title=Freshwater Algae in Northwest Washington, Volume II, Chlorophyta and Rhodophyta | url= https://cedar.wwu.edu/cedarbooks/1/ | journal = A Collection of Open Access Books and Monographs | publisher = Western Washington University | doi=10.25710/fctx-n773 }}</ref> and associated with desmids. A few species prefer alkaline habitats, such as ''Eremosphaera minor'' which grows in alkaline soil.<ref>{{cite journal|title=''Eremosphaera tanganyikae'' sp. nov. (Trebouxiophyceae), a new species from Lake Tanganyika|first1=Maya|last1=Stoyneva|first2=Georg|last2=Gärtner|first3=Christine|last3=Cocquyt|first4=Wim|last4=Vyverman|journal=Belgian Journal of Botany|volume=139|issue=1|date=2006|pages=3–13|jstor=20794590}}</ref> Because of its large size, it is used as a model organism to study cell physiology.<ref name=AlgaeBase/>
The genus name comes from the Greek roots ''eremos'', meaning "solitary", and ''sphaira'', meaning "ball".<ref name=CarolinaLucidKey>{{cite web|url=https://fmp.conncoll.edu/Silicasecchidisk/LucidKeys3.5/Keys_v3.5/Carolina35_Key/Media/Html/Eremosphaera_Main.html|title=Eremosphaera|first1= Hannah|last1= Shayler|first2=Peter A.|last2=Siver|work=Carolina Lucid Key to Freshwater Algae|publisher=Connecticut College | date=2004 |access-date=2025-02-04 }}</ref>
==Description== ''Eremosphaera'' consists of relatively large cells which are solitary or in clusters of two to four, with or without a mucilaginous envelope. Cells are spherical to ellipsoidal 23–130 × 20–120 μm, with a thick cellulosic cell wall up to 1 μm thick. Some species are thickened at the poles, while one species (''Eremosphaera oocystoides'') has spicules covering the surface. The cytoplasm is filled with a large central vacuole with radial strands of cytoplasm which connect the nucleus to its periphery. The cytoplasm may have numerous oil droplets, granules, or calcium oxalate crystals. The central nucleus is about 5 to 31 μm in diameter, with up to five nucleoli. Each cell has many parietal (sometimes radial) chloroplasts; the chloroplasts are discoid, with one to three pyrenoids.<ref name=AlgaeBase/>
Asexual reproduction occurs via the formation of autospores; two to four are produced per sporangium and these are released through a rupture in the parental cell wall.<ref name=AlgaeBase/> Sexual reproduction has only been documented in on species, ''E. viridis'', and is oogamous and homothallic. Sixteen to 64 sperm cells produced in an antheridium, and are biflagellate, spherical and lack plastids or a stigma. Egg cells are similar in morphology to autospores; when fertilized, zygotes produced thickened walls.<ref name=AlgaeBase/>
==Classification== ''Eremosphaera'' is classified in the subfamily Eremosphaeroideae of the family Oocystaceae, along with ''Oocystaenium'' and ''Excentrosphaera''.<ref name=Komarek_Fott>{{cite book | title= Chlorophyceae (Grünalgen), Ordnung Chlorococcales | last1=Komárek | first1=J. | last2=Fott | first2=B. | date=1983 | publisher= E. Schweizerbart'sche Verlagsbuchhandlung | series=Das Phytoplankton des Süßwassers | language=German | pages=1044 }}</ref> The subfamily is distinguished by having relatively large cells, many chloroplasts, and a smooth cell wall. It is unclear whether it is monophyletic, since phylogenetic studies often find it as a basal evolutionary grade to the rest of Oocystaceae.<ref name=Stenclova>{{cite journal|doi=10.1111/jpy.12581 |title=Molecular and morphological delimitation and generic classification of the family Oocystaceae (Trebouxiophyceae, Chlorophyta) |date=2017 |last1=Štenclová |first1=Lenka |last2=Fučíková |first2=Karolina |last3=Kaštovský |first3=Jan |last4=Pažoutová |first4=Marie |journal=Journal of Phycology |volume=53 |issue=6 |pages=1263–1282 |pmid=28833138 |bibcode=2017JPcgy..53.1263S }}</ref>
Species are distinguished from each other based on details of morphology, namely the size and shape of the cells and their chloroplasts.<ref name=Komarek_Fott/> However, the genus is in need of taxonomic revision,<ref name=AlgaeBase/> and is not monophyletic as currently circumscribed.<ref name=Stenclova/>
==References==
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Category:Trebouxiophyceae genera Category:Oocystaceae Category:Freshwater algae Category:Model organisms