Frustulia esandalliae is one of only a handful of Frustulia species with capitate apices. It is easily separated from F. amosseana and F. spicula by its larger size. It is very similar in size and shape to F. alfinitosilviae but has a wider, more elliptic and less linear central area (3.0-5.1 μm wide, not 1.5-2.0 μm wide) and more closely spaced areolae (24-26 in 10 μm, not 17-20 in 10 μm).