• Category
  • Length Range
    7-20 µm
  • Width Range
    4-8.5 µm
  • Striae in 10 µm
  • Reported As
    Planothidium dubium (this site)



Valves are linear-elliptic, with narrowly subcapitate to capitate apices. The raphe valve has a linear axial area and transversely rectangular central area. The raphe is straight with expanded external proximal ends.

The rapheless valve has a narrow, linear axial area. The asymmetric central area on the rapheless valve contains a shallow depression on the internal valve surface. The striae are radiate throughout both valves.

Note that the historical concept of P. dubium (as Achnanthes lanceolata ssp. dubia (Krammer and Lange-Bertalot 1999)) included both taxa that are currently recognized as P. dubium and P. reichardtii. The specimens presented on this page conform to the description of P. reichardtii.

However, it is not clear if P. dubium is present in North America.


This taxon has been recorded in rivers, across a wide range of environmental conditions. It has been recorded in recent surveys of the western US.

Original Description

Valvae ad instar ellipticae ad lineari-ellipticas apicibus fere abrupte protractis subcapitatis vel paene capitatis (non elliptico-lanceolatae apicibus paulatim protractis substratis ad apiculatos). Longitudo 8-18 µm, latitudo 4-6.5 µm. Raphe et area axialis etiam striae vix differentes, sed area centralis areovalvarum semper angustius extendens. Depressio simplex vix (non caverna formans) in forma ferri equini formata sed magis in positu trianguli dilatata ad marginem versus. Microscopio electronico vix altera signa distinguenda. In loco typico associata cum P. dubium.

  • Author
    Lange-Bertalot and Werum 2004
  • Length Range
    8-18 µm
  • Width
    4-6.5 µm

Original Images

Planothidium Reichardtii Orig Ill2
Planothidium Reichardtii Orig Ill1
Planothidium Reichardtii Orig Desc


May 01, 2020 - Change of name

From 2011 until May 2020, this taxon appeared as Planothidium dubium (Grun.) Round and Bukht. on Diatoms of North America. - M. Potapova

Cite This Page

Potapova, M. (2011). Planothidium reichardtii. In Diatoms of North America. Retrieved May 18, 2024, from https://diatoms.org/species/planothidium_reichardtii


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Planothidium reichardtii 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.