Cladonia didyma is a fruticose lichen, commonly known as southern soldiers, belonging to the family Cladoniaceae, which include fungal symbionts under the Ascomycota phylum with characteristic red ascocarps containing sexually reproductive asci.

Variation of micro physiological features include  presence or absence of  a medulla or cortex, and surface textures that can be grooved, smooth, or velvety.

[5][6][9] Among the many phenotypes of C. didyma, two major chemotypes have been defined by the presence of either didymic or thamnolic acid and are observed within different habitat types.

[9] Analysis of C. didyma metabolites has found antioxidant compounds as well as others within chemical families associated with defense responses related to oxidative stress and UV exposure.

[10] Cladonia didyma has a wide distribution and can be found on nearly every continent and oceanic region[11] under various environmental conditions, at sea level and altitudes as high as 3400 meters,[3][5][9] and habitats ranging from mesic to xeric forests.