Pediastrum Meyen, 1829

Lectotype species: Pediastrum duplex Meyen

Original publication: Meyen, F.J.F. (1829). Beobachtungen über einige niedere Algenformen. Nova Acta Physico-Medica Academiae Caesareae Leopoldino-Carolinae Naturae 14: 768-778, pl. XLIII [43].

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Description: Thalli colonial, comprising 4-64 (-128) celled coenobia, 15-400 &m diameter, arranged in a flat, circular to oval plate, one cell thick. If 16 or more cells, cells tend to be in concentric rings; each ring with definite number of cells; disc continuous or with perforations between cells. Ring development dependent upon zoospore behavior at coenobial formation. Cell 8-32 &m diameter, with highly variable shape, interior cells typically polyhedral with four to many sides; peripheral cells similar or with one or two horn-like processes. Peripheral cells often with bristles not found in central cells. Cells walls smooth, finely reticulate or highly granulate. Cells multinucleate; diffuse chloroplast single and parietal; pyrenoid one or more per cell. Asexual reproduction mostly via coenobial formation after production of biflagellate zoospores. Every cell in colony capable of coenobial formation but this rarely synchronous. Zoospores released from parental cell wall in vesicle that persists throughout period of swarming and shortly after new coenobium formed. Vesicle derived from inner cell wall layer of parental cell. Zoospore number species specific and also dependent on physiological condition of cells. Vesicle release usually occurs shortly after daybreak and zoospores swim freely within vesicle before arranging themselves in flat plate when movement stops and cells assume adult shape. Asexual reproduction by thick-walled resting spores in P. simplex, these developing in old cultures. Spores spherical, 8-50 &m and orange with roughened cell walls. After transfer to fresh medium spores turn green and produce zoospores. Cells in initial coenobium spherical; peripheral cells with one or two processes. Normal cell morphology returns with subsequent coenobial production. Sexual reproduction in Pediastrum infrequently reported; life history of P. simplex similar to Hydrodictyon reticulatum. Isogamous, spindle-shaped, biflagellate gametes 2.5-8 &m smaller than zoospores but formed similarly. Gametes with single chloroplast and eyespot; gametes align in parallel or posterior to posterior. Following syngamy spherical zygote increases in size and develops biflagellate zoospores released through opening in cell wall. After free-swimming stage zoospores develop into solitary Tetraedron-like cells that increase in size and then undergo zoospore formation and coenobial production as in asexual reproduction. Ultrastructurally, gametes of P. duplex, similar to Hydrodictyon, with mating structure or 'apical cap'. Pediastrum planktonic, virtually ubiquitous and often abundant in permanent or temporary freshwater pools; from arctic to tropical climates throughout the world. Phosphorus physiology studied in P. duplex. Bristles present on some species; these develop from prongs of peripheral cells and can exceed 100 &m in length. Bristles in tufts of up to 80 hexagonal tubules with specific substructure. Bristle removal results in rapid colony sinking. Cells walls unusual among green algae in having a significant component of silicon; walls also with crystalline component of D-glucose and D-mannose units organized in non-microfibrillar network of interwoven chains of rings.Species distinguished based on cell size and shape, especially peripheral cells, and colony morphology.

Information contributed by: D. Garbary & T. Harper. The most recent alteration to this page was made on 2012-07-10 by Michael Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Most recent taxonomic treatment adopted: Tsarenko, P.M. (2011). Sphaeropleales. In: Algae of Ukraine: diversity, nomenclature, taxonomy, ecology and geography. Volume 3: Chlorophyta. (Tsarenko, P.M., Wasser, S.P. & Nevo, E. Eds), pp. 280-355. Ruggell: A.R.A. Gantner Verlag K.-G..

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Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

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Citing AlgaeBase
Cite this record as:
Michael Guiry in Guiry, M.D. & Guiry, G.M. 10 July 2012. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 21 November 2024