Pilzgattungen: Obeliospora [3 Taxa], Obolarina [1 Taxon], Obstipipilus [1 Taxon], Obstipispora [1 Taxon], Ocellaria [7 Taxa], Ocellularia [212 Taxa], Ochroconis [45 Taxa], Ochrolechia [204 Taxa], Ochropsora [28 Taxa], Ocotomyces [6 Taxa], Octaviania [3 Taxa], Octavianina [3 Taxa], Octospora [41 Taxa], Octosporella [2 Taxa], Odontia [22 Taxa], Odontia [12 Taxa], Odonticium [3 Taxa], Odontiopsis [1 Taxon], Odontodictyospora [2 Taxa], Odontotrema [14 Taxa], Odontura [2 Taxa], Oedemium [4 Taxa], Oedocephalum [26 Taxa], Oedothea [1 Taxon], Ohleria [7 Taxa], Oidiodendron [81 Taxa], Oidiopsis [52 Taxa], Oidium [1987 Taxa], Ojibwaya [4 Taxa], Oligonema [7 Taxa], Oligoporus [2 Taxa], Oligostroma [35 Taxa], Olivea [34 Taxa], Oliveonia [1 Taxon], Ollula [1 Taxon], Olpidiopsis [10 Taxa], Olpidium [34 Taxa], Olpitrichum [8 Taxa], Ombrophila [25 Taxa], Omega [5 Taxa], Ommatospora [1 Taxon], Ommatosporella [1 Taxon], Omnidemptus [2 Taxa], Omphalia [32 Taxa], Omphalia [9 Taxa], Omphalina [45 Taxa], Omphalopsis [15 Taxa], Omphalospora [5 Taxa], Omphalotus [7 Taxa], Oncobasidium [2 Taxa], Oncopodiella [3 Taxa], Oncopodium [23 Taxa], Oncospora [46 Taxa], Oncosporomyces [2 Taxa], Onychophora [1 Taxon], Onygena [9 Taxa], Oomyces [1 Taxon], Oospora [26 Taxa], Oothecium [14 Taxa], Opegrapha [8 Taxa], Opegrapha [324 Taxa], Operculella [5 Taxa], Ophiobolus [139 Taxa], Ophioceras [14 Taxa], Ophiociliomyces [6 Taxa], Ophiocordyceps [5 Taxa], Ophiodothella [55 Taxa], Ophiognomonia [4 Taxa], Ophiomassaria [4 Taxa], Ophionectria [60 Taxa], Ophioparodia [1 Taxon], Ophiosphaerella [17 Taxa], Ophiostoma [322 Taxa], Ophiostomella [3 Taxa], Ophiovalsa [19 Taxa], Oplophora [2 Taxa], Oramasia [2 Taxa], Orbicula [4 Taxa], Orbilia [281 Taxa], Orbiliaster [2 Taxa], Ordus [2 Taxa], Oreophylla [1 Taxon], Oropogon [13 Taxa], Orphanocoela [1 Taxon], Orthobellus [1 Taxon], Osmoporus [80 Taxa], Ossicaulis [13 Taxa], Osteina [5 Taxa], Ostracoderma [4 Taxa], Ostreichnion [5 Taxa], Ostreola [6 Taxa], Ostropa [17 Taxa], Ostropella [4 Taxa], Oswaldoa [7 Taxa], Otidea [8 Taxa], Otthia [123 Taxa], Otthiella [1 Taxon], Oudemansiella [65 Taxa], Ovularia [186 Taxa], Ovulariopsis [91 Taxa], Ovulinia [1 Taxon], Oxydothis [12 Taxa], Oxyporus [128 Taxa], Ozonium [43 Taxa]