Placoneis Mereschkowsky, 1903

Lectotype species: Placoneis gastrum (Ehrenberg) Mereschkowsky

Original publication: Mereschkowsky, C. (1903). Über Placoneis, ein neues Diatomeen-Genus. Beihefte zum Botanischen Centralblatt 15(1): 1-30, pl. 1.

Type designated in: Cox, E.J. (1987). Placoneis Mereschkowsky: the re-evaluation of a diatom genus originally characterized by its chloroplast type. Diatom Research 2(2): 145-157.

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Description: Cells solitary, rectangular in girdle view, with a single H-shaped chloroplast. It consists of two elongated arms, connected by a narrow isthmus in the center of the valve. Valve outline variable, from linear-elliptic to lanceolate, apices acutely or broadly rounded, subcapitate, subrostrate, capitate or rostrate. Raphe often filiform, proximal raphe ends expanded and curved to the same or opposite sides. Distal raphe ends curved to the same side. In some species it seems that they are oppositely curved, but in SEM it is clear that one of the terminal fissures recurves and forms a hook-like ending. Intermissio present. Axial area usually narrow, central area variable. Isolated pores (stigmoids) may be present (up to four on the same valve). Their openings are round externally and round or oval internally. Striae uniseriate, sometimes shortened and more widely spaced in the central valve region. Areolae round externally and usually square internally. Areolae are occluded by pseudotectula.

Information contributed by: Mironov & al. 2024. The most recent alteration to this page was made on 2024-06-07 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 feminine.

Most recent taxonomic treatment adopted: Mironov, A., Glushchenko, A., Maltsev, Y., Genkal, S., Kuznetsova, I., Kociolek, J.P., Liu, Y. & Kulikovskiy M. (2024). Reassessment of pore occlusion in some diatom taxa with re-evaluation of Placoneis Mereschkowsky (Bacillariophyceae: Cymbellales) and description of two new genera. PeerJ 12(e17278): 1–62, 10 figures, 4 tables.

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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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in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.

Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=44201

Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 07 June 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 22 November 2024