Guide to Pinnularia alabamae
- Valves large, linear, with inflated middle
- Apices subcapitate to cuneate
- Axial area 1/4–1/3 valve width
- Longitudinal line present
- Spines occasional
The valves are large, linear, with an inflated middle part and subcapitate-cuneate apices. The axial area is linear and about 1/4–1/3 of the valve width. The striae are crossed by two longitudinal lines: one transects the striae about 4–7 μm from axial area, while another line is positioned 2–5 μm from the valve margin - sometimes not visible with LM. Spines are occasionally present on the valve face-mantle junction, located between the striae.