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Placoneis explanata

(Hust.) Mayama in Mayama and Kawashima 1998      Category: Symmetrical biraphid
BASIONYM: Navicula explanata Hust. 1948

Placoneis anglophila


Placoneis gastrum

LM scalebar = 10 µm = 80 pixels.


Contributor: David R.L. Burge | Mark Edlund - June 2017
Length Range: 22-37 µm
Width Range: 8.5-11.4 µm
Striae in 10 µm: 10-12 at the valve center, 17-19 at the apices


Valves are linear-lanceolate, with weakly convex margins. Apices are rostrate and bluntly rounded. The axial area is linear and narrow. The central area is variable, from bow-tie to rectangular in shape. The raphe is straight and weakly lateral. The proximal raphe ends are weakly inflated. The distal raphe ends are deflected to opposite sides of one another. Striae are radiate and weakly curved at the center of the valve, becoming straight, parallel and finally, more dense at the apices. The striae on the primary side occur 11-12 in 10 µm and on the secondary side, 10-11 in 10 µm. The areolae are round to slightly apically elongate and occur 24-26 in 10 µm.

This taxon was originally described as Navicula explanata Hustedt (1948) and later transferred to Placoneis explanata (Hustedt) Mayama in Mayama and Kawashima (1998). Lange-Bertalot published a later homonym (Placoneis explanata (Hustedt) Lange-Bertalot in Rumrich et al. 2000 nom. illegit). The earlier name, P. explanata (Hustedt) Mayama in Mayama and Kawashima has priority.

Original Description

Basionym: Navicula explanata
Author: Hust. 1948
Length Range: 28-32 µm
Width Range: 9-11 µm
Striae in 10 µm: 12 in the valve center, 20 in the ends

Original Description

Original Images

Cite This Page:
Burge, D., and Edlund, M. (2017). Placoneis explanata. In Diatoms of the United States. Retrieved May 23, 2018, from

Species: Placoneis explanata

Contributor: David R.L. Burge | Mark Edlund

Reviewer: Sarah Spaulding


Cumming, B.F., Wilson, S.E., Hall, R.I. and Smol, J.P. (1995). Diatoms from British Columbia (Canada) Lakes and their relationship to salinity, nutrients and other limnological variables. Bibliotheca Diatomologica 31: 1-207.

Fallu, M.-A., Allaire, N. and Peinitz, R. (2000). Freshwater diatoms from northern Québec and Labrador (Canada). Species-environment relationships in lakes of boreal forest, forest-tundra and tundra regions. Bibliotheca Diatomologica 45: 1-200.

Foged, N. (1981). Diatoms in Alaska. Bibliotheca Phycologica, Band 53, J. Cramer, Vaduz, 317 pp.

Hofmann, G., Lange-Bertalot, H., and Werum, M. (2013). Diatomeen im Süßwasser-Benthos von Mitteleuropa: 2 Corrected Edition. Koeltz Scientific Books, Königstein, 908 pp.

Hustedt, F. (1948). Die Diatomeenflora diluvialer Sedimente bei dem Dorfe Gaj bei Konin im Warthegebiet. Schweizerische Zeitschrift für Hydrologie 11: 181-209. 10.1007/BF02503311

Mayama, S. and Kawashima, A. (1998). New combinations for some taxa of Navicula and Stauroneis, and avowed substitute for a taxon of Eunotia. Diatom 14: 69-71.

Moser, K.A., Smol, J.P. and MacDonald, G.M. (2004). Ecology and distribution of diatoms from boreal forest lakes in Wood Buffalo National Park, Northern Alberta and the Northwest Territories, Canada. The Academy of Natural Sciences of Philadelphia, Special Publication Number 22, 59 pp.

Rumrich, U., Lange-Bertalot, H. and Rumrich, M. (2000). Diatoms of the Andes. From Venezuela to Patagonia/Tierra del Fuego and two additional contributions. Lange-Bertalot, H. (ed.), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 9. Phytogeography-Diversity-Taxonomy. Koeltz Scientific Books, Königstein, Germany, 9:673 pp.

Links & ID's

Index Nominum Algarum (INA)

Original INA
Transfer INA

California Academy of Sciences (CAS)

Placoneis explanata CAS

North American Diatom Ecological Database (NADED)

NADED ID: 194007

Autecology Discussion

Placoneis explanata has been reported in North America from ponds in Alaska (Foged 1981), lakes in British Columbia (Cumming et al. 1995), Québec, Labrador (Fallu et al. 2000), Alberta and the Northwest Territories (Moser et al. 2004). It is also known from Utah and Connecticut (Patrick and Reimer 1966). The specimens illustrated here are from sediments of Moody Lake in Minnesota.

It has also been reported from lakes and rivers of Japan (Mayama and Kawishima 1998) and Europe (Hofmann et al. 2013).