This may sound like a dumb question, but is the plural form of genera ending in -ium actually -ia (example, Oncidia or Cymbidia) when you are referring to more than one individual plant of these genera. How about Phalaenopses for more than one phal? Any ideas?
Not dumb at all. I'm not sure either. I've always said Cymbidiums or Oncidiums, and I avoid using the plural of Phalaenopsis all together. Let's hear from an expert...
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 )
Oncidia is the plural of Oncidium only if you are speaking or writing in Latin. It would be wrong to use it in a sentence written in English. Oncidiums is appropriate but actually incorrect usage as well (but nobody realy cares). The correct phrases would be "species of Oncidium" or "hybrids of Oncidium". And as an aside, "Oncidium species" is also technically wrong because it implies that the nature of a species in Oncidium is different than the nature of a species in some other genus since Oncidium becomes a modifier of species.