Some marks on leaves are caused not by animals, but by microbes such as fungi or bacteria. On living plants, fungal leaf spots and blights often become more common during wet seasons because moisture promotes spore germination and growth. These infections can produce a wide range of patterns, from tiny speckles to large discolored patches, sometimes with diffuse edges or a halo-like ring. Unlike chewing damage, microbial lesions usually do not show clear “bite” margins or repeated, mandible-shaped notches. Instead, they tend to look like tissue discoloration or decay spreading across the leaf surface, sometimes following veins or appearing as many similar spots scattered across the leaf. In fossil leaves, it can be difficult to diagnose microbial infection with certainty because preservation and mineral staining can mimic discoloration, so researchers consider the overall pattern, consistency across specimens, and preservation context when making interpretations. Well-known modern examples include powdery mildew, rust fungi, and anthracnose, which produce white coatings, rust-colored spots, or dark necrotic lesions on leaves. In addition, sap-feeding insects such as aphids and leafhoppers can transmit plant viruses, meaning that insect feeding and microbial infection may occur together. Such combined interactions suggest that complex plant–insect–microbe relationships may also have deep roots in the fossil record.