• Category
  • Length Range
    6-9 µm
  • Width Range
    3.3-4.2 µm
  • Striae in 10 µm
    28-32 on raphe valve, 25-28 on rapheless valve



Valves are linear-elliptical, slightly constricted in the middle. The raphe valve has a linear axial area, which widens into a small circular or elliptical central area. The raphe is straight and lacks terminal fissures. Externally, the central and terminal raphe ends are very slightly expanded externally. Internally, the central raphe ends curve toward opposite sides internally. The rapheless valve has a large rhomboid axial area. The central area is usually not differentiated from the axial area on rapheless valve. Striae are radiate on both valves and interrupted at the valve margin. Striae number 28-32 in 10 µm on raphe valve and 25-28 in 10 µm on rapheless valve . One row of areolae is present on the mantle of both valves. The external openings of the areolae are square or rectangular.


Original Description

Schalen linear-elliptisch mit parallelen bis schwach konkaven Seiten und breit gerundeten Enden, 6-8 μ lang, 3.5-4 μ breit. Raphenlose Schalen mit breit linearer Pseudoraphe, Transapikalstreifen kurz, sehr wenig radial, 26-28 in 10 μ. Raphenschale mit feiner, fadenförmiger Raphe mit einander genäherten Zentralporen, Axialarea sehr eng, um den Mittelknoten kaum erweitert; Transapikalstreifen 30-34 in 10 μ, in der Mitte kräftiger als vor den Polen, senkrecht zur Mittellinie oder nur wenig radial, besonders vor den Polen.

  • Basionym
    Achnanthes didyma
  • Author
    Hust. 1933
  • Length Range
    6-8 µm
  • Width
    3.5-4 µm
  • Striae in 10µm

Original Images

Orig Ill 1
Orig Descr 3

Cite This Page

Potapova, M. (2010). Psammothidium didymum. In Diatoms of North America. Retrieved May 20, 2024, from https://diatoms.org/species/psammothidium_didymum


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