The term stratified, when used in reference to a lichen, refers to a lichen that exhibits partitioning of algal and fungal partners within the thallus (contrast with non-stratified).
Stratification is displayed in this cross section of Tuckermannopsis orbata. The dense top layer is the upper cortex (fungal cells); just below is the more loosely packed photobiont layer (interwoven with fungal hyphae). Below the photobiont layer is the fungal medulla, which shows as loose, webby material. (Electron micrograph A. Fischer--1/2011)