{{short description|Genus of algae}} {{Automatic taxobox | taxon = Planctonema | authority = Schmidle | type_species = Planctonema lauterbornii | type_species_authority = Schmidle<ref name=AlgaeBase>{{AlgaeBase genus|id=43490|name=Planctonema|access-date=2025-02-05}}</ref> | subdivision_ranks = Species | subdivision = * ''Planctonema sp. M110-1'' * ''Planctonema sp. J45-9'' * ''Planctonema lauterbornii'' | synonyms = }}
'''''Planctonema''''' is a genus of green algae in the class Trebouxiophyceae.<ref>See the NCBI [https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=163319 webpage on Planctonema]. 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 is found in freshwater habitats as plankton,<ref name=AlgaeBase/> and is found worldwide. It is dominant in lakes during the summer and autumn months.<ref name=Liu>{{cite journal|doi= 10.1111/jpy.12551|title= Classification of ''Planctonema''-like algae, including a new genus ''Planctonemopsis'' gen. nov., a new species ''Planctonema gelatinosum'' sp. nov. and a reinstated genus ''Psephonema'' (Trebouxiophyceae, Chlorophyta)|date= 2017|last1= Liu|first1= Xudong|last2= Zhu|first2= Huan|last3= Liu|first3= Benwen|last4= Liu|first4= Guoxiang|last5= Hu|first5= Zhengyu|journal= Journal of Phycology|volume= 53|issue= 4|pages= 869–879|pmid= 28542872|bibcode= 2017JPcgy..53..869L}}</ref>
The classification of ''Planctonema'' has varied historically. It was originally described by Wilhelm Schmidle as a heterokont, and has also been placed in the family Ulotrichaceae. Molecular phylogenetic evidence has shown that ''Planctonema'' is closely related to members of the family Oocystaceae,<ref name=Liu/> and AlgaeBase places ''Planctonema'' in Oocystaceae.<ref name=AlgaeBase/> However, it lacks the cell wall ultrastructure characteristic of the family.<ref name=Liu/>
==Description== ''Planctonema'' consists of short, uniseriate filaments surrounded in a common mucilaginous sheath. Individual cells. Individual cells are spaced apart equidistantly, or end-to-end in separate pairs; the space between cells is filled with mucilage. Cells are cylindrical, with a parietal, plate-like chloroplast without pyrenoids or starch. The nucleus is located in the median constriction of the chloroplast. At the ends of the cell poles are vacuoles containing conspicuous oil globules.<ref name=AlgaeBase/>
Vegetative reproduction occurs by the fragmentation of filaments. Sexual reproduction is unknown.<ref name=AlgaeBase/>
Similar genera include ''Psephonema'' (formerly considered to be synonymous with ''Planctonema''), and ''Planctonemopsis'', described in 2017. ''Psephonema'' has shorter cells than ''Planctonema'' (with a length–width ratio of 1.5–2, while ''Planctonemopsis'' has chloroplasts with pyrenoids).<ref name=Liu/>
==References== {{Reflist}}
{{Taxonbar|from=Q7200993}}
Category:Trebouxiophyceae genera Category:Freshwater algae Category:Oocystaceae
{{green algae-stub}}