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Navicula flatheadensis

L.L.Bahls 2011      Category: Symmetrical biraphid

Navicula escambia


Navicula freesei

LM scalebar = 10 µm = 40 pixels.


Contributor: Loren Bahls - December 2011
Length Range: 45-75 µm
Width Range: 10.3-13.5 µm
Striae in 10 µm: 10-12


Valves are lanceolate, narrowing gradually to weakly protracted and rounded ends. The axial area is narrow, widening gradually into an irregularly rounded but nearly symmetrical central area. The raphe is weakly lateral. External raphe fissures run close to the edge of the axial area from the poles to the central area, where they return to mid-valve, giving them a bowed appearance. Proximal raphe ends are relatively distant and terminate in curved, trumpet shaped pores that are deflected to the primary side of the valve. The raphe sternum and central nodule appear to have relief. The central nodule is half again wider than the raphe sternum and typically asymmetrical, with one flat and one convex side, or it may be symmetrical with both sides convex. Distal raphe fissures are hooked. Striae are radiate, more widely spaced and somewhat bent near the central area, becoming parallel to weakly convergent at the ends. Areolae in the striae are distinct and number 24-28 in 10 µm.

Original Description

Author: L.L.Bahls 2011
Length Range: 45-75 µm
Width Range: 10.3-13.5 µm
Striae in 10 µm: 10-12

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.

Original Images

Cite This Page:
Bahls, L. (2011). Navicula flatheadensis. In Diatoms of the United States. Retrieved May 23, 2018, from

Species: Navicula flatheadensis

Contributor: Loren Bahls

Reviewer: Marina Potapova


Bahls, L.L. (2011). Three new species of Navicula (Bacillariophyta) from Oregon and Montana and a review of diatom endemism in the Northwest. Northwest Science 85 (4): 517-526.

Lange-Bertalot, H. (2001). Navicula sensu stricto, 10 genera separated from Navicula sensu lato, Frustulia. Diatoms of Europe 2: 1-526.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

North American Diatom Ecological Database (NADED)


Autecology Discussion

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). N. flatheadensis shares some of these same habitats with N. subconcentrica, with which it is easily confused.


Lake Winona, Glacier National Park, Montana: type locality for Navicula flatheadensis.

Credit/Source: E. William Schweiger, National Park Service