The scanning-electron microscope was used to examine the cortical surface of 123 species of lichens in 12 genera of the lichen family Parmeliaceae. Two general types of cortex were found, one consisting of exposed hyphae and one with the hyphae covered by a thin polysaccharide epicortex. The epicorticate species fell into two groups, one with a tightly appressed continuous epicortex and one with a more loosely associated pored epicortex. Type of epicortex is a constant character at the genus and section level and appears to have considerable usefulness in the taxonomy of the family.
