Stephanodiscus hantzschii has nearly flat valves and finer areolae. Stephanodiscus agassizensis and S. oregonicus have fascicles that become at least triseriate at the valve margin. Spines are often absent from marginal interfascicles in S. agassizensis.

LM scalebar = 10 µm
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

Stephanodiscus oregonicus

(Ehrenb.) Håk. 1986

Stephanodiscus oregonicus LM7 Stephanodiscus oregonicus LM6 Stephanodiscus oregonicus LM5 Stephanodiscus oregonicus LM4 Stephanodiscus oregonicus LM3 Stephanodiscus oregonicus LM2 Stephanodiscus oregonicus LM1
13.0-25.6 µm
Striae in 10 µm
Fascicles 3-4

Stephanodiscus hantzschii

Grunow in Cleve and Grunow 1880

Stephanodiscus hantzschii LM7 Stephanodiscus hantzschii LM4 Stephanodiscus hantzschii LM3 Stephanodiscus hantzschii LM6 Stephanodiscus hantzschii LM1
11.8-20.3 µm
Striae in 10 µm
6-9 fascicles based on circumferential count

Also compare to

Stephanodiscus agassizensis

Håk. and H.J.Kling