Light micrograph of a section through the lobe of Peltigera aphtosa, through a Cephalodium. The thallus is dotted with cephalodia, which contain one of the two symbionts, a cyanobakterium, species Nostoc, identifiable by the olive-green color. Nostoc is located inside the Cephalodia in small clusters. The other symbiont, a green alga genus Coccomyxa, is located under the surface of the lobe in a thin, continuous layer, seen at the left of the image. Microscopic contrast method : oblique brightfield with fluorescence overlay. Magnification 380x when printed at 10 centimetres wide.