That ‘…ium’ sure sounds latin to me. Let’s check. Referring to Webster’s Collegiate Dictionary, Fifth Addition, copyright 1942, the word comes from latin, based on the words nasus (nose) + torquere (twist). “Nose-twist, in allusion to it’s pungency.” So there you have it. An old Roman nose twister. Nasturtium.
But Wait! I live in modern America. The good old U.S.A., where a great deal of our communal attention is engaged with big events which happen stadiums across the country. Yes, stadiums. When the Indianapolis Colts play football at home, they play in their own stadium. When they travel, they play in various other stadiums. No one says they play in other stadia. (Well, actually….. I do! But don’t tell anyone.)
So really, it is OK. Call these little beauties nasturtiums. Or call them nasturtia. But please, whichever you call them, know that you have a choice.