The correct plural for Oncidium and Cymbidium is -dia, but using -ums in normal language is laos normal practice among biologists... as per Phalaenopsis.. I am not sure, but I know that the director of the molecular genetics Dept. at the Botanical Garden in Berlin would say "Phalaenopsis" and would not worry at all... (she just mentioned that 1 minute ago on the phone

)
she also laughed about me for asking
