• Category
  • Length Range
    17.8-29.5 µm
  • Width Range
    5.0-5.8 µm
  • Striae in 10 µm
    13-16 at mid-valve; up to 18 at the apices



Valve outline is broadly clavate and lanceolate, with a broadly rounded headpole and narrower footpole. The striae are weakly radiate and uniseriate, becoming more radiate at the footpole. The axial area is broad. A stigma is located in the central area. The raphe is straight and lateral, with external proximal raphe ends dilated and bending slightly.

In the SEM, the striae are composed of distinctive C-shaped areolae.

A number of species of Gomphonema with a broad axial area are found in eastern and southeastern rivers. In past surveys, this taxon has likely been confused with G. entolejum Lange-Bertalot (as shown in Lange-Bertalot and Krammer 1987, Pl. 40, Figs 18-19) and G. clevei (as shown in Hustedt 1937-1939, Pl. 27, Figs 15-18). Gomphonema incognitum has C-shaped areolae (visible in SEM), which are not found in G. entolejum or G. clevei.


Gomphonema incognitum was described from eastern Nepal, so it has an unexpected disjoint distribution in rivers of the southeast U.S. It has been verified in samples from Georgia, North Carolina and Alabama. All of the sites where it occurs the southeast are low in nutrients and considered least-impacted sites.

Original Description

Valvae late clavatae-lancolatae verticibus obtuse rotundatis, polis basalibus aliquantum minus late rotundatis. Longitudo 17-39 mm, latitudo 4-6.5 mm. Raphe leniter lateralis, fissuris externis undulatis. Extrema centralia externa internaque aspectabilia, extrema interna in eadem partem declinata. Area universalis late rhombico-lanceolata, stigma solitaria prope nodulum centralem posita. Striae transapicales curtae modice radiate, sub polos magis radiatae, in media parte valvarum parallelae, 14-16 in 10 mm. Puncta striatum plerumque tenuissime vel indistincte discernanda. Frustula aspectu cincturae paulo cuneiformia. Puncta vel alterae structurae in limbis vacant.

  • Author
    E.Reichardt, Jüttner and E.J.Cox 2004
  • Length Range
    17-39 µm
  • Width
    4-6.5 µm
  • Striae in 10µm

Original Images

Gomp Incognitum Orig Desc Plate1
Gomp Incognitum Orig Desc Plate2
Gomp Incognitum Orig Desc Text

Cite This Page

Bishop, I. (2016). Gomphonema incognitum. In Diatoms of North America. Retrieved June 21, 2024, from https://diatoms.org/species/gomphonema_incognitum


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