• Category
  • Length Range
    45-75 µm
  • Width Range
    10.3-13.5 µm
  • Striae in 10 µm



Valves are lanceolate, narrowing gradually to weakly protracted and rounded ends. The axial area is narrow, widening gradually into an irregularly rounded but nearly symmetric central area. The raphe is weakly lateral. Externally, the raphe is positioned close to the edge of the axial area from the poles to the central area, where the raphe is positioned in the middle of the axial area. The proximal raphe ends are relatively distant and terminate in curved, trumpet shaped pores. The pores are deflected to the primary side of the valve. The raphe sternum and central nodule are positioned above the valve surface. The central nodule is half again wider than the raphe sternum. The sternum is typically asymmetric, with one flat and one convex side, or it may be symmetric with both sides convex. The distal raphe fissures are hooked. Striae are radiate and more widely spaced and somewhat bent near the central area. The striae become parallel to weakly convergent at the ends. Areolae in the striae are distinct and number 24-28 in 10 µm.


Navicula flatheadensis is known only from four headwater lakes in the Flathead River Basin of northwest Montana. These lakes have alkaline pH (range 7.1-8.3) and low concentrations of dissolved solids (range 90-250 µS/cm). Navicula flatheadensis shares some of these same habitats with N. subconcentrica.

Original Description

Valves lanceolate with gradually attenuated and rounded ends. Length 45-75 μm, width 10.3-13.5 μm. Axial area narrow, widening into a rounded central area. Raphe sternum laterally expanded in the center. Raphe weakly lateral, outer raphe fissure runs close to the edge of the axial area from the poles to near the central area, where it returns to the midline. Central raphe fissures nearly straight, ending in small cup-shaped pores that are widely separated (Figure 1G, I). Distal raphe fissures curved, concave toward the secondary side. Striae radiate and somewhat bent, becoming parallel to weakly convergent at the ends, 10-12 in 10 μm, more widely spaced about the central area. Areolae distinct, 24-28 in 10 μm, visible in LM.

  • Author
    Bahls 2011
  • Length Range
    45-75 µm
  • Width
    10.3-13.5 µm
  • Striae in 10µm

Original Images

Nflat Origimage
Nflat Origdesc

Cite This Page

Bahls, L. (2011). Navicula flatheadensis. In Diatoms of North America. Retrieved July 13, 2024, from https://diatoms.org/species/navicula_flatheadensis


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