• (1) Obconicum chaerophylli - Octaviania borziana
• (2) Octaviania brisbanensis - Oidium papillatum
• (3) Oidium parthenii - Omphalia stellata
• (4) Omphalia straminea - Opegrapha amphotera
• (5) Opegrapha angulosa - Opegrapha unicolor
• (6) Opegrapha urosperma - Ophiovalsa trichispora
• (7) Ophiovalsa valsoides - Ovularia simplex
• (8) Ovularia sommeri - Ozonium aureum