Fragilaria vaucheriae and F. recapitellata have wider, shorter valves. Fragilaria vaucheriae, F. recapitellata, and F. capucina have wider, alternate striae. The central areas of large valves of F. vaucheriae and short valves of F. capucina can be entirely hyaline. Fragilaria vaucheriae and F. capucina have rostrate apices with only one rimoportula per valve. Ulnaria ulna has a central area that is bilateral and not expanded and may contain ghost striae.