{{Short description|Genus of single-celled organisms}} {{Italic title}} {{Automatic taxobox | image = Pinnularia major.jpg | image_caption = ''Pinnularia major'', {{Nowrap|specimen length 0.3 mm}} | taxon = Pinnularia | authority = Ehrenberg | subdivision_ranks = Species }}

'''''Pinnularia''''' is a genus of fresh water algae, more specifically a type of diatom.<ref>{{cite web|url=https://diatoms.org/genera/pinnularia |accessdate=20 June 2019 |title=Pinnularia - Ehrenberg 1843 |website=Diatoms.org}}</ref>

==Habitat== ''Pinnularia'' is a predominantly fresh-water algae usually found in ponds and moist soil.<ref>{{cite book |url=https://books.google.com/books?id=kwVHAQAAMAAJ&pg=PA37 |pages=37–38 |title=Pond-life: Algae and Allied Forms |author=T. Spencer Smithson |publisher=Swan Sonnenschein |year=1890}}</ref> They can also be found in springs, estuaries, sediments, and oceans. Members of this genus are most commonly found in {{convert|40|cm|in|abbr=on}} of water, at {{convert|5|°C|°F}}.{{Citation needed|date=January 2026}}

==External structure== thumb|''Pinnularia opulenta'' ''Pinnularia'' are elongated elliptical unicellular organisms. Their cell walls are composed chiefly of pectic substances on a rigid silica framework, and composed of two halves called thecae (or less formally, valves). These halves overlap like a Petri dish and its cover, the outer larger valve called Epitheca and the smaller called hypotheca. The margins of the two thecae are covered by a connecting band called a cingulum and all together are referred to as a frustule, and the whole cell is covered by a mucilaginous layer. The surface view is called valve view and band view is called girdle view.<ref>{{cite book |url=https://books.google.com/books?id=9y9TOUinTqoC&pg=PA382|page=382|title=Botany for Degree Students: Algae|author1=Vashishta B.R.|author2=Sinha A.K.|author3=Singh V.P.|publisher=S. Chand Publishing|year=2010|isbn=9788121935210|orig-date=First pub. 1960}}</ref>

==Internal structure==

The cytoplasm is arranged approximately in layers conforming to the shape of the cell's walls. A large central vacuole is present with the nucleus suspended in its centre by a transverse cytoplasmic bridge. Two chloroplasts are present along the sides of the cells, and contain chlorophyll a, c, beta-carotene and fucoxanthin pigments. One or two pyrenoids are usually present in each chloroplast, although like many heterokont algae, ''Pinnularia'' tend to store their energy as fat. The cytoplasm also contains chrysolaminarin and some volutin.{{Citation needed|date=January 2026}}

==Reproduction== thumb|''Pinnularia'' diatom during reproduction (cell division) {{Details|Diatom#Life-cycle}} ''Pinnularia'', like most diatoms, can reproduce by simple cell division. Nuclear division occurs by mitosis and cell divides into two parts. Each daughter receives one of the parent cell's thecae, which becomes that cell's epitheca. The cell then synthesizes a new hypotheca. Thus, one daughter is the same size as the parent, and one is slightly smaller. With subsequent generations, the average cell size of a ''Pinnularia'' population gradually becomes smaller. When a minimum average size is reached, auxospore formation occurs and sexual reproduction restores the population's average cell size.{{Citation needed|date=January 2026}}

==References== {{Reflist}}

==External links== [https://www.algaebase.org/search/species/detail/?tc=accept&species_id=31984 ''Pinnularia major'' (Kützing)]

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{{Heterokont}} {{Taxonbar|from=Q920264}} {{Authority control}}

Category:Diatom genera Category:Naviculales Category:Taxa named by Christian Gottfried Ehrenberg