Dark brown, angular spots with gray flecks.

Close-up of the underside of the leaf showing dark brown, angular spots with gray flecks.

One infected area of leaf where dark brown, spore-producing bodies ("pycnidia") can be seen within the spots.

Close-up of infected area with dark brown, spore-producing bodies ("pycnidia").

Dark-field observation of long, thin spores of a species of the fungus Septoria.

Long, thin spores of a species of the fungus Septoria.