• Category
  • Length Range
    37.2-81.3 µm
  • Width Range
    6.5-10.3 µm
  • Striae in 10 µm
  • Synonyms
    Navicula bisulcata Lagerst. 1873
    Schizonema bisulcatum (Lagerst.) Kuntze 1898



Valves are linear and elongate, with rounded apices. A longitudinal canal is present along each valve margin. The valve face is flat. Areolae are elongate along the transapical axis.

Striae are parallel to slightly oblique across the valve face, becoming convergent near the apices. The angle of the striae differs at the apices, with the more strongly converging striae occurring on opposite sides of the raphe at each apex. The central area is oval to rhombic. Voigt discontinuities are subtle, when present.

Proximal raphe ends are long and reflexed in opposite directions toward the valve margins (~100°). Proximal raphe ends tend to extend to the edge of the central area. Specimens commonly display a single irregular raphe end, pointing anywhere from 0° to 180°.

The axial area expanded asymmetrically near apices. The raphe is an oblique slit.

Internally, valves bear a rectelevatum. Helictoglossae are robust, and are noticeably larger than those of Neidium capsulare. Lacinia are difficult to resolve.

The specimens documented in the Rocky Mountains of Colorado conform well to the original description of Lagerstedt (1873). This taxon, however, may have been confused with other similar taxa historically. In European literature, it has been included within a broad morphological species concept (Lange-Bertalot et al. 2017).

A number of Neidium taxa have similar linear, elongate valve margins. Particular attention should be paid to the valve outline, width, and proximal raphe ends.


This taxon is typical of in alpine habitats in Colorado, particularly seeps and springs. It was found growing in association with Microcostatus krasskei, as well as taxa in the genera Psammothidium and Pinnularia. This species appears to prefer habitats rich in decaying plant material.

N bisulcatum live
Credit: Lane Allen
Live cell of N. bisulcatum
James Peak North Face Pool2
Credit: Lane Allen
A small spring where Neidium bisulcatum, Microcostatus krasskei, Psammothidium, and Pinnularia can be found.
Neidium bisulcatum Initial Valve from Allenspark, CO
Credit: Lane Allen
An extremely large specimen that must have recently undergone sexual reproduction.

Original Description

Frustulum a fronte lineare, marginibus levissime concavis, apicibus rotundatis vel cuneato-rotundatis; a latere rectangulare, angulis rotundatis. Nodulus centralis oblongus; noduli terminales rotundati. Linea media e lineis duabus rectis composita. Striæ et transversales et longitudinales inconspicuæ. Area longitudinalis linearis, circa nodulos dilatata. Sulci longitudinales duo, marginibus paralleli. Color frustuli exsiccati pallide lutescens. Long. 40-70 µ. Lat. 8-9 µ.

Spetsb. Parrys ö; Brandewije B. Liefde B. Smeerenberg B. Amsterdam ön; Dansk ön; Kobbe B. Isfjorden; Nordfjorden; Cap Thordsen (sötvatten); Advent B. Green Harbour.

Beer. Eil. (jord och mossa)

Denna art är närmast beslägtad med de till gruppen Limosæ Grun. Hörande arter. Den utmärkes isynnerhet genom de två längsgående fårorna. Synes stå nära N. alpestris Grun. som dock saknar sådana fåror.

  • Basionym
    Navicula bisulcata
  • Author
    Lagerst. 1873
  • Length Range
    40-70 µm
  • Width
    8-9 µm

Original Images

Neidium bisulcatum original image2
Neidium bisulcatum original description1

Cite This Page

Allen, L. (2022). Neidium bisulcatum. In Diatoms of North America. Retrieved September 26, 2023, from https://diatoms.org/species/neidium-bisulcatum


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