Microthamnion

{{Short description|Genus of algae}} {{Automatic taxobox | image=Microthamnion.jpg | image_caption=''Microthamnion'' sp. | taxon = Microthamnion | authority = Nägeli | type_species = ''Microthamnion kuetzingianum'' | type_species_authority = Nägeli ex Kützing<ref name=AlgaeBase/> | subdivision_ranks = Species | subdivision = * ''Microthamnion kuetzingianum'' }}

'''''Microthamnion''''' is a genus of green algae in the family Microthamniaceae.<ref>{{AlgaeBase taxon|name=''Microthamnion'' taxonomy|id=87976}}</ref><ref name=AlgaeBase>{{AlgaeBase genus|name=Microthamnion|id=42758}}</ref> It is found in freshwater habitats around the world, preferably with low levels of pollution;<ref name=AlgaeBase/> it is typically attached to solid substrates.<ref name=Matthews/>

==Description== ''Microthamnion'' consists of a microscopic, branched system of erect filaments. The filaments are uniseriate, with cylindrical cells; terminal cells are obtuse. Cells range from 1-5 μm wide and 2-15 times longer than wide.<ref name=Reder/> New branches form just underneath the cross-walls connecting cells. Cells are uninucleate (i.e. with one nucleus with a parietal chloroplast and no visible pyrenoids.<ref name=AlgaeBase/><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>

Reproduction occurs asexually via the formation of bottle-shaped zoospores, which are formed in vegetative cells that develop into sporangia. Typically this occurs in the terminal cells, but any cell except for the most basal may produce zoospores.<ref name=Reder/> The zoospores have two flagella and up to 32 are produced per sporangial cell.<ref name=John2014>{{cite book |editor-first1=John D.|editor-last1=Wehr|editor-first2=Robert G.|editor-last2=Sheath|editor-first3=J. Patrick|editor-last3=Kociolek |date= 2014 |edition=2 |title= Freshwater Algae of North America: Ecology and Classification |last1= John|first1=David M.| last2=Rindi |first2=Fabio |chapter= Chapter 8. Filamentous (Nonconjugating) and Plantlike Green Algae |url= |location= |publisher= Elsevier Inc. |page= |isbn=978-0-12-385876-4 }}</ref>

==Taxonomy== ''Microthamnion'' was first described by Carl Nägeli in 1849 in Friedrich Traugott Kützing's work ''Species algarum''. It is recognized as a well-defined genus, but its placement has varied. Initially placed in the family Ulotrichaceae, at times, it has been placed in Trentepohliaceae and Chaetophoraceae until finally being placed in its own family. Currently, it is placed within its own family and order in the class Trebouxiophyceae.<ref name=Reder>{{cite thesis|title=A case study of species delimitation with molecular methods: the algal genus Microthamnion (Microthamniales, Trebouxiophyceae)|last1= Reder|first1=T.|date=2019|location= Köln|publisher= Universität zu Köln|pages= i-xii, 1-109 |url=https://kups.ub.uni-koeln.de/10406/}}</ref>

The species-level taxonomy of this genus is unclear, since individuals display a wide range of morphological variation. Many names have been given to forms which may be mere growth forms and not taxonomically informative.<ref name=John2014/><ref name=AlgaeBase/> As a consequence, opinions on the number of species vary widely, ranging from as few as one very polymorphic species<ref>{{cite journal|doi=10.1016/S0003-9365(11)80269-1 |title=A Molecular and Morphological Analysis of Microthamnion (Chlorophyta, Microthamniales) |date=1993 |last1=John |first1=D.M. |last2=Bhoday |first2=R. |last3=Russell |first3=S.J. |last4=Johnson |first4=L.R. |last5=Gacesa |first5=P. |journal=Archiv für Protistenkunde |volume=143 |issue=1–3 |pages=33–39 }}</ref> to as many as fourteen putative species.<ref name=Reder/>

==References==

Category:Microthamniales Category:Trebouxiophyceae genera Category:Freshwater algae