Lange-Bertalot 2001 Category: Symmetrical biraphid
BASIONYM: Navicula subconcentrica Lange-Bertalot 2001
Contributor: Loren Bahls - November 2011
Length Range: 36-58 µm
Width Range: 8.5-10.6 µm
Striae in 10 µm: 10-12
Valves are lanceolate and narrow gradually to weakly protracted acutely rounded ends, or apices narrow abruptly to form protracted, subcapitate ends. The axial area is narrow and widens gradually to a small, more or less rhombic central area. The raphe sternum and central nodule appear raised in relief. The central nodule is half again wider than the raphe sternum and has flat or occasionally concave sides. The raphe is weakly lateral and nearly straight along the valve midline. Proximal raphe ends are nearly straight and relatively close together. Raphe pores are distinct and deltoid in shape. Terminal raphe fissures are hooked, the hooks opening toward the secondary side. The striae are strongly radiate throughout and become parallel only at the poles. Areolae in the striae are distinct and number 24-27 in 10 µm.
Basionym: Navicula subconcentrica
Author: Lange-Bertalot 2001
Length Range: 40-64 µm
Width Range: 9-10 µm
Striae in 10 µm: 10.5-12.0
Valves lanceolate, gradually narrowing to weakly protracted acutely rounded ends, length 40-64 microns, breadth 9-10 microns. Raphe slightly sinuous, weakly lateral with distinct central pores in a comparatively narrow position. Axial area (very) narrow distally widening gradually to a small central area with various outlines due to some irregularly shortened median striae. Striae rather strongly radiate, some short ones in subpolar position parallel or very indistinctly convergent, 10.5-12/10 microns; lineolae arranged as in Navicula concentrica but less coarse than in that species, c. 27-29/10 microns. SEM (Fig. 30: 12): Sternum relief-like prominent on the valve outside, expanded in the centre. Central pores short, drop-like, not hooked and only slightly deflected to the secondary valve side.
Lange-Bertalot, H. (2001). Navicula sensu stricto, 10 genera separated from Navicula sensu lato, Frustulia. Diatoms of Europe 2: 1-526.
There are 13 records of Navicula subconcentrica in the Montana Diatom Collection, most of them from lakes and ponds in the Canadian Rockies Ecoregion (Glacier and Waterton Lakes National Parks), where it prefers alkaline waters (mean pH = 8.2) of modest conductivity (mean SC = 315 µS/cm). Common diatom associates of N. subconcentrica in the Northern Rockies are Sellaphora parapupula, Navicula schadei, Navicula wildii, Placoneis explanata, Navicula jaagii, Cymbella transilvanica, Cymbella laevis v. lata, Fragilaria capucina v. austriaca, Cymbopleura inaequalis, Encyonopsis descripta, Cymbella frigida, and Neidium apiculatum. Lange-Bertalot (2001) described this species from material collected in an oligotrophic chalk-rich lake in Bavaria.
Governor Pond, Glacier National Park, Montana: home of Navicula subconcentrica
Credit/Source: Loren Bahls