• Category
  • Length Range
    154-231 µm
  • Width Range
    40-49 µm
  • Striae in 10 µm
  • Synonyms
    Navicula dilatata Ehrenb. 1843
    Schizonema dilatatum (Ehrenb.) Kuntze 1898



Valves are large and lanceolate, with gently cuneate apices. Five or more narrow longitudinal lines are present on the valve margin. The valve face is nearly flat. The central area is transapically elliptic and broad. The central area is up to 1/3 of the valve width.

Striae are evenly spaced and composed of distinct areolae. Striae are weakly radiate to parallel at the central valve (0-5°). Striae become more convergent at the apices (18-26°). Striae may be oblique near the center and toward the apices.

The raphe is an oblique slit, becoming filiform near the proximal raphe ends. Proximal raphe ends are small and tightly hooked in opposite directions. The angle of deflection of the proximal raphe end varies from ~90° to ~180°.

In SEM, the areolae are small round to elliptic and weakly recessed (Hamilton et al. 2015). Renilimbia are identifiable around the axial areolae. Areolae form interconnected chambers inside the valve wall, and fine criba are present inside the areolae (Hamilton et al. 2015).


This taxon is present in low conductivity and soft water habitats. They have been found co-occurring with species of acidophilic genera, including species of Eunotia and Iconella (formerly reported as Stenopterobia spp.). Neidium species grow unattached and are found in benthic or wetland habitats. These specimens were collected from Paulsen Mine in Cook County, MN, and Parker Dam State Park in Clearfield County, PA. The Paulsen Mine site contained significant populations of N. amphigomphus and N. fossum.

Other distributional and ecological records include several wetland sites in the northeast around Adirondack Park in New York State (Hamilton et al. 2019). Significant co-occurrence with N. amphigomphus, N. fossum, N. tumescens, and other Neidium species indicate that N. dilatatum shares habitats with these species and may have a similar distribution.

Ehrenberg originally described a population of dilatatum within a high-altitude soil sample by a colleague, Dr. Thirke. The location is described as "Dshimil-bashi hilltop" in German, at approximately 9,000 feet in elevation (Ehrenberg 1843) in the Turkish region of Bithynia (formerly Asia Minor).

LB1335 105 1 35 6 internal
Credit: Andrew Burgess
Internal view of N. dilatatum apex showing the helictoglossa. Scale bar = 10 μm.
LB1335 105 1 35 6
Credit: Andrew Burgess
Comparison view of the same valve showing the distal raphe end with the helictoglossa out of focus. Scale bar = 10 μm.

Original Description

140. N. dilatata, magna a dorso elliptico-lanceolata, lateribus leviter convexis, longitudinaliter lineolatis, apicibus obtusis

  • Basionym
    Navicula dilatata
  • Author
    Ehrenb. 1843
  • Length Range
    164-264 µm
  • Width
    39-56 µm
  • Striae in 10µm

Original Images

Navicula dilatata Ehren orig image 1854 pl4section2 Smithfield Rhode Islandfig9
Navicula dilatata Ehren orig image 1854 pl4section1 Stratfordfig5
Navicula dilatata Ehren orig image 1854 pl3section2 Andowerfig5
Neidium dilatatum orig image

Cite This Page

Burgess, A. (2023). Neidium dilatatum. In Diatoms of North America. Retrieved September 23, 2023, from https://diatoms.org/species/neidium-dilatatum


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