Mae gan lawer o ffyngau berthynas symbiotig bwysig ag organebau o'r rhan fwyaf os nad pob [[Teyrnas (bioleg)|teyrnas]].<ref name="Aanen2006" /Perotto1997><ref{{cite namejournal | vauthors="Nikoh2000"Perotto /><refS, nameBonfante P | title="Perotto1997"Bacterial associations with mycorrhizal fungi: close and distant friends in the rhizosphere | journal=Trends in Microbiology | volume=5 | issue=12 | pages=496–501 | date=December 1997 | pmid=9447662 | doi=10.1016/S0966-842X(97)01154-2 }}</ref> Gall y rhyngweithiadau hyn fod yn gydfuddiannol neu'n elyniaethus eu natur, neu yn achos ffyngau cymesurol nid ydynt yn amlwg o unrhyw fudd nac anfantais i'r gwesteiwr.<ref name="Arnold2003"Hube2004>{{cite journal | vauthors=Hube B | title=From commensal to pathogen: stage- and tissue-specific gene expression of ''Candida albicans'' | journal=Current Opinion in Microbiology | volume=7 | issue=4 | pages=336–41 | date=August 2004 | pmid=15288621 | doi=10.1016/j.mib.2004.06.003 }}</ref><ref name="Paszkowski2006" /><ref{{cite namejournal | vauthors="Hube2004"Paszkowski U | title=Mutualism and parasitism: the yin and yang of plant symbioses | journal=Current Opinion in Plant Biology | volume=9 | issue=4 | pages=364–70 | date=August 2006 | pmid=16713732 | doi=10.1016/j.pbi.2006.05.008 }}</ref>
