(Brébisson) W. Smith 1856 Category: Symmetrical biraphid
BASIONYM: Navicula polyonca Brébisson in Kützing 1849
Contributor: Loren Bahls - March 2012
Length Range: 68-80 µm
Width Range: 8.9-10.3 µm
Striae in 10 µm: 10-12
Valves are rhombic-lanceolate with a triundulate outline, the middle expansion is wider than the distal ones. Apices are capitate and rounded. The axial area is very wide and lanceolate in shape. The central area is a transverse fascia. In some populations, there are one or two short striae on the secondary side of the fascia. The raphe is lateral. Proximal raphe ends are curved to the primary side. Terminal raphe fissures are shaped like question marks. Striae are very short and radiate in the middle, becoming longer and strongly convergent towards the apices.
With their shorter striae, less swollen middles, and broad axial areas with distinct markings, the specimens pictured above belong to P. polyonca var. stidolphii. Thanks to Paul Hamilton for this observation.
Basionym: Navicula polyonca
Author: Brébisson in Kützing 1849
Length Range: µm
Striae in 10 µm:
Krammer, K. (1992). Die Gattung Pinnularia in Bayern. Hoppea 52: 1-308.
Krammer, K. (2000). The genus Pinnularia. The Diatoms of Europe. Diatoms of Inland Waters and Comparable Habitats 1: 1-703.
Krammer, K. and Lange-Bertalot, H. (1986). Bacillariophyceae. 1. Teil: Naviculaceae. In: Ettl, H., J. Gerloff, H. Heynig and D. Mollenhauer (eds.) Süsswasserflora von Mitteleuropa, Band 2/1. Gustav Fisher Verlag, Jena. 876 pp.
Kützing, F.T. (1849). Species Algarum. Lipsiae. F.A. Brockhaus, 922 pp.
Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.
Smith, W. (1856). Synopsis of British Diatomaceae. John Van Voorst, London 1856. 2: 107pp., pls. 32-60, 61-62, A-E.
Pinnularia polyonca has been found in two small lakes and a floating-mat fen in western Montana. All three sites have abundant vascular plant growth. The pH of these sites ranges from 6.73 to 7.41 and specific conductance ranges from 22 to 257 µS/cm.
Skinner Lake, Beaverhead National Forest, Montana: home of Pinnularia polyonca.
Credit/Source: Loren Bahls