• Category
  • Length Range
    19-24 µm
  • Width Range
    6.2-7.3 µm
  • Striae in 10 µm



Valves are lanceolate, with subrostrate apices. The raphe valve has a linear axial area. The central area is variable, from transversely rectangular to elliptic. The raphe is straight, with expanded external proximal ends. The rapheless valve has a linear-lanceolate axial area. The central area is asymmetric and contains a cavum on the internal valve surface. On both valves the striae are multiseriate and slightly radiate throughout.

This species was recently separated from Planothidium biporomum. That taxon differs by capitate apices.

Recent investigation shows that Planothidium biporomum has a more restricted distribution than the widespread P. incuriatum (Wetzel et al. 2013). These taxa have been confused in surveys of North America. Further work will clarify the records of each of these species.


This species was described from France. In North America, it was found in the EPA National Lakes Survey (2017).

Original Description

Planothidium incuriatum C.E. Wetzel, Van de Vijver & Ector sp. nov. (Figs 19-36, 51-89)

Light microscopy (Figs 19-36, 62-79): - Valves lanceolate to elliptic-lanceolate with convex margins and rostrate, protracted apices. Valve dimensions (n=30): length 18.0-25.4 µm, width 6.4-7.0 µm. Rapheless valve (Figs 19-27, 62-70). Axial area narrow, straight linear. Central area with a unilateral large horseshoe-shaped hyaline area with a cavum clearly visible. On the opposite side, striae either not shortened sometimes slightly shortened striae forming hence a small circular area (Fig. 24). Striae weakly radiate throughout the entire valve. Between 13 and 15 striae in 10 µm measured at the central part of the valve opposite to the unilateral expression. Raphe valve (Figs 18-36, 71-79). Axial area narrow, linear, widening near the central area. Central area rectangular to slightly rounded, bordered on each side by usually two up to three shortened striae. Raphe branches straight with expanded, drop-like proximal raphe endings. Distal raphe fissures unilaterally deflected. Striae radiate throughout the entire valve, 13-15 in 10 µm. Areolae not discernible in LM.

  • Basionym
    Planothidium incuriatum
  • Author
    Wetzel, Van de Vijver and Ector 2013
  • Length Range
    18-25.4 µm
  • Width
    6.4-7 µm
  • Striae in 10µm

Original Images

Planincuriatum  Orig

Cite This Page

Potapova, M. (2019). Planothidium incuriatum. In Diatoms of North America. Retrieved September 25, 2021, from https://diatoms.org/species/planothidium_incuriatum


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