• Category
  • Length Range
    4.9-8.5 µm
  • Width Range
    3.5-4.0 µm
  • Striae in 10 µm



Valves are elliptical to linear-elliptical. The raphe valve has a linear axial area and a small transversely elongated central area formed by one to three shortened striae on each side. The raphe is straight, without terminal fissures. The central and terminal raphe ends are slightly expanded externally. The central raphe ends curve toward opposite sides internally. The rapheless valve has a linear-lanceolate or narrowly rhomboid axial area, and a small transversely elongated central area. Striae are radiate on both valves, 27-31 in 10 µm, interrupted at the valve margin. One row of areolae is present on the mantle of both valves. External openings of the areolae on the raphe valve are large, square or rectangular, occasionally elongated. Such openings on the rapheless valve are usually small, circular to silt-like. Internal openings of the areolae on the faces of both valves are square, on the mantle they are elliptical.


Original Description

Valve oval with rounded ends about 7 μ long and 3 μ wide. Raphe valve with straight delicate raphe and approximate central pores, longitudinal space narrow lanceolate, central space wanting, striae radiate throughout about 33 in 10 μ the central one on each side being curtailed. Rapheless valve with lanceolate pseudo-raphe and no central space, striae less radiate than those of the complementary valve about 30 in 10 μ.

  • Basionym
    Achnanthes curtissima
  • Author
    J.R.Carter 1963
  • Length Range
    7 µm
  • Width
    3 µm
  • Striae in 10µm

Original Images

Or Ill001 1
Or Descr001 1

EMAP Assessment

EMAP Distribution

Achnanthes Curtissima 40 Copy
Map 40

Response Plots

Achnanthes Curtissima

Cite This Page

Potapova, M. (2010). Psammothidium curtissimum. In Diatoms of North America. Retrieved April 06, 2020, from https://diatoms.org/species/psammothidium_curtissimum


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