Achnanthidium kranzii is similar to A. minutissimum in valve shape and size, but can be distinguished from A. minutissimum by the curved terminal raphe fissures that are usually visible in LM. In addition, A. kranzii has wider valves (on average), a large rectangular central area on the raphe valve and a distinct rhomboid, or apically elliptical, central area on the rapheless valve.