The cork warts on leaves of plants appear to be a response to mechanical injuries or pathogen penetrations. Many of Gnetum species regularly form cork warts on leaf surfaces and stems. We have searched anatomy, morphology and development of cork warts and also estimated evaluation of probable influence to its origin by phylloplane fungi. Leaves of two species of Gnetaceae family G. gnemon and G. montanum have been investigated for anatomical and morphological studies of cork warts and for mycological research. Herbarial specimens of 13 Gnetum species have been searched. We have successfully extracted 15 species of phylloplane ascomycetes that appear to influence negatively on continuity of leaf epidermis and being able to existing as parasites as well. The most frequent species were Cladosporium cladosporioides which became a dominant indicating 100% of frequency index and representatives of Fusarium and Phoma genera. The frequency index of latter numbered 36 and 20% correspondingly. Five species of Penicillium ascomycetes were also determined as frequent. Cork warts have been found in 13 species of Gnetum that grow in natural environment. Cells in local areas of epidermis and subepidermal layers proliferate periclinally during cork wart development in leaves of G. gnemon and G. montanum. As a result, the layer of high compactly packaged cells emerges. Tannins inside cell compartments and suberinization of cell walls were indicated for cork warts. It emphasizes a defensive function of the structures. Cork warts appear to originate like "Patches" on the surfaces of leaves of evergreen gnetum plants.