Was that my original guess? I don't recall that. I sometimes sing "amaranthus" but I don't have reason to think it was misremembered from anything in particular – how about "Oculatus"? I can decipher the Latin meaning or "aronatus" if it was supposed to mean something, but beyond that I don't know its origin.

Incidentally, there were many mentions of an "Alba Oculata" in botanical books of the period, described as "white with a blue eye," but that was a type of Phlox Drummondii. It's another possibility, though not a bright blue to my eye.