Stephanodiscus niagarae can be distinguished from S. reimeri by the areola density; 11-20 vs 8-12 in 10 µm, respectively. These two species can also be distinguished by the size and shape of the areolae. While S. niagarae has small, round areolae, S. reimeri has unusually shaped trapezoidal to sub-hexagonal areolae. Stephanodiscus alpinus has comparatively large, hyaline interfascicles (costae), each with a spine at the valve face margin. In contrast, S. reimeri has a marginal spine at the end of every 2-3 costae. Compared to S. reimeri, S. superiorensis is smaller (39-72 µm), only slightly arched in the valve center, and has spines on every third or fourth costa.

LM scalebar = 10 µm
Stephanodiscus reimeri LM3 Stephanodiscus reimeri LM7 Stephanodiscus reimeri LM6 Stephanodiscus reimeri LM1 Stephanodiscus reimeri LM4
35-120 µm

Stephanodiscus niagarae

Ehrenb. 1845

Ill2011 41  Steph Niagarae6 Ill2011 41  Steph Niagarae5 Ill2011 41  Steph Niagarae2 Ill2011 41  Steph Niagarae3 Ill2011 41  Steph Niagarae
21-70 µm

Stephanodiscus alpinus

Hust. in Hub.-Pest. 1942

Stephanodiscus alpinus LM3 Stephanodiscus alpinus LM7 Stephanodiscus alpinus LM2 Stephanodiscus alpinus LM11 Stephanodiscus alpinus LM6 Stephanodiscus alpinus LM5 Stephanodiscus alpinus LM4
13.8-30.8 µm
Striae in 10 µm
12-14 fascicles

Also compare to

Stephanodiscus superiorensis

Stoermer and E.C.Ther.