• Category
  • Length Range
    22.3-37.2 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.


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).

Original Description

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

Original Images

Naexplanata  Originalimage
Naexplanata  Originaltext

Citations & Links



Cite This Page

Burge, D, and Edlund, M. (2017). Placoneis explanata. In Diatoms of North America. Retrieved August 18, 2018, from https://diatoms.org/species/placoneis_explanata


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Placoneis explanata from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.