Placoneis
Mereschkowsky 1903 Category: Symmetrical biraphid
TYPE SPECIES: Placoneis gastrum (Ehrenberg) Mereschkowsky
Image Credit: Ditmar Metzeltin
CLASS: Bacillariophyceae
ORDER: Cymbellales
FAMILY: Cymbellaceae
- Valve linear to lanceolate
- Ends sometimes rostrate to capitate
- Striae uniserate
- Stigmata present or absent
The valve outline of Placoneis is linear to lanceolate, sometimes with rostrate or capitate ends. The areolae are loculate and internally occluded. Areolae form uniseriate striae. The axial area is narrow. The proximal raphe ends are straight and slightly expanded externally. The plastid is large, distinct, and divided into two X-shaped plates.
Placoneis contains a number of species that grow in epipelic habitats of lakes and streams. It includes the former Placoneis exigua (Gregory) Mereschkowsky and its allies. The taxonomic position of the genus is unclear, as it has been suggested to hold naviculoid as well as cymbelloid and gomphonemoid affinities (Mann & Stickle 1995, Kociolek & Thomas 2010).
Cite This Page:
Spaulding, S., Edlund, M., and Metzeltin, D. (2009). Placoneis. In Diatoms of the United States. Retrieved May 22, 2013, from http://westerndiatoms.colorado.edu/taxa/genus/Placoneis
Contributor: Sarah Spaulding | Mark Edlund | Ditmar Metzeltin - January 2009
Reviewer: Sam Rushforth
Citations
Cox, E.J. (1987). Placoneis Mereschkowsky: the re-evaluation of a diatom genus originally characterized by its chloroplast type. Diatom Research 2: 145-157.
Cox, E.J. (2003). Placoneis Mereschkowsky revisited: resolution of several typification and nomenclatural problems, including the generitype. Bot. J. Linn. Soc. 141: 53–83. 10.1046/j.1095-8339.2003.00115.x
Jahn, R. (2004). Discovery of the type specimen of Pinnularia gastrum Ehrenberg, the type species of the genus Placoneis Mereschkowsky. Diatom Research 19: 229–234.
Kociolek, J.P. and Thomas, E.W. (2010). Taxonomy and ultrastructure of five naviculoid diatoms (class Bacillariophyceae) from the Rocky Mountains of Colorado (USA), with the description of a new genus and four new species. Nova Hedwigia 90:195-214. 10.1127/0029-5035/2010/0090-0195
Levkov, Z., Krstic, S., Metzeltin, D. and Nakov, T. (2007). Diatoms of Lakes Prespa and Ohrid: about 500 taxa from ancient lake system. Iconographia Diatomologica 16: 1-613.
Mann, D.G. and Stickle, A. (1995). Sexual reproduction and systematics of Placoneis (Bacillariophyta). Phycologia 34: 74-86.
Metzeltin, D. and Lange-Bertalot, H. (1998). Tropical diatoms of South America I: About 700 predominantly rarely known or new taxa representative of the neotropical flora. In: Lange-Bertalot, H. (ed.), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 5. Diversity-Taxonomy-Geobotany. Koeltz Scientific Books. Königstein, Germany, 5:695 pp.
Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.
May 1st, 2011 - correction of type species
The generitype had been posted as Placoneis exigua (Gregory) Mereschkowsky. Is was corrected to Placoneis gastrum (Ehrenberg) Mereschkovsky based on Cox (2003) and Jahn (2004).