Krammer 2000 Category: Symmetrical biraphid
BASIONYM: Pinnularia nodosa var. percapitata Krammer 2000
Contributor: Loren Bahls - March 2014
Length Range: 43-70 µm
Width Range: 7.7-10.6 µm
Striae in 10 µm: 10
Valves are linear with triundulate margins. In the largest specimens, the central undulation is wider than the distal undulations. Apices are distinctly capitate. Axial areas are about one-third the valve width and become wider from the apices towards the valve center. The central area is a bilateral fascia. The surface of the valve is mottled along either side of the raphe, continuing into the central area. The raphe is straight. Proximal raphe ends are bent to one side and terminate in small tear-shaped pores. Distal raphe fissures are shaped like question marks. Striae are weakly radiate at the valve center, becoming strongly convergent at the apices.
Basionym: Pinnularia nodosa var. percapitata
Author: Krammer 2000
Length Range: 47-61 µm
Width Range: 9-10 µm
Striae in 10 µm: 8-10
Krammer, K. (2000). The genus Pinnularia. The Diatoms of Europe. Diatoms of Inland Waters and Comparable Habitats 1: 1-703.
The specimens of P. nodosa var. percapitata observed are from streams, ponds and small lakes in the northern Rocky Mountains of Montana. At these locations pH ranged from 6.10 to 7.78 and specific conductance ranged from 22 to 169 µS/cm. Water quality preferences of this variety appear to be similar to those of the nominate variety: low to moderate electrolyte content and low pH, most commonly found in peaty bogs and in springs (Krammer 2000).
Indian Meadows Research Natural Area, Helena National Forest, Lewis & Clark County, Montana: home of Pinnularia nodosa var. percapitata.
Credit/Source: Loren Bahls