Euastrum Ehrenberg ex Ralfs, 1848

Lectotype species: Euastrum ansatum Ehrenberg ex Ralfs

Original publication: Ralfs, J. (1848). The British Desmidieae The drawings by Edward Jenner, A.L.S. pp. [i]-xxii, [i], [1]-226, 35 pls. London: Reeve, Benham & Reeve, King William Street, Strand.

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Type designated in: Guiry, M.D. (2013). Taxonomy and nomenclature of the Conjugatophyceae (=Zygnematophyceae). Algae. An International Journal of Algal Research 28: 1-29.

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Description: Cells solitary, usually longer than broad, with deep median constriction (isthmus) shere semicell walls overlap. Apical view oval to elliptical (biradiate), often with broadened middle region (rare triangular forms known). Each semicell usually with distinct apical and lateral lobes; apical lobe with emarginate apex or apical incision. Cell wall smooth with scattered pores, or variously ornamented with granules, verrucae or short spinules. Usually one chloroplast per semicell with one or more pyrenoids. Nucleus in isthmus. Asexual reproduction by cell division and new semicell morphogenesis characteristic of Cosmarium-type desmids (see Cosmarium). Sexual reproduction by conjugation. Conjugating cells pair and form gelatinous envelope. Gametes fuse between gametangia. Mature zygospores globose to ellipsoidal with many short, acute spines or mamillate protuberances. Euastrum commonly collected from acidic, oligotrophic, aquatic habitats or from bogs. Several species cosmopolitan. Euastrum cannot be distinguished with absolute confidence from Cosmarium or Micrasterias; placement of certain taxa is arbitrary.

Information contributed by: J.F. Gerrath. The most recent alteration to this page was made on 2023-11-13 by M.D. Guiry.

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

Gender: This genus name is currently treated as neuter.

Most recent taxonomic treatment adopted: Guiry, M.D. (2013). Taxonomy and nomenclature of the Conjugatophyceae (=Zygnematophyceae). Algae. An International Journal of Algal Research 28: 1-29.

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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in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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M.D. Guiry in Guiry, M.D. & Guiry, G.M. 13 November 2023. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway.; searched on 22 February 2024

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