• Category
  • Length Range
    11–16 µm
  • Width Range
    5.7–7.0 µm
  • Striae in 10 µm
  • Synonyms
    Planothidium stewartii (R.M.Patrick) Lange-Bert. in Krammer and Lange-Bert.



Valves are elliptic. Both valves have a linear axial area. The central area on the raphe valve is transapically rectangular, often reaching the valve margin. The central area on the rapheless valve is small and often asymmetric. The striae are radiate and biseriate. The raphe is straight, filiform and lacks terminal fissures. Distal external raphe ends are slightly expanded and straight. Proximal external raphe ends are expanded and sharply turned to one side. Areolae are round. There is a row of areolae on the valve mantle, with one areola at the end of each stria.


Platessa stewartii was shown to have preference for a low calcium content, while its conductivity optimum (based on a dataset of 2674 river samples from the USA) was 134 μm/cm (Potapova & Charles 2003).

Original Description

Valvae ellipticae, 16 μ longae, 7.5 μ latae, area axiali angusta, costis tenuibus 14 in 10 μ, serie duplici punctorum parvorum interpositu

  • Basionym
    Achnanthes stewartii
  • Author
    R.M.Patrick 1945
  • Length Range
    16 µm
  • Width
    7.5 µm
  • Striae in 10µm

Original Images

Orig Ill  Plstew
Orig Descr  Plstew

EMAP Assessment

EMAP Distribution

Planothidium Stewartii 40 Copy
Map 40

Response Plots

Planothidium Stewartii Copy

Cite This Page

Potapova, M. (2010). Platessa stewartii. In Diatoms of North America. Retrieved July 23, 2018, from https://diatoms.org/species/planothidium_stewartii


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