Hi again Janet, Thanks for the memory jog. I think you're referring to an Invalid (abbreviation=I.) name. I've run across that myself although I can't recall precisely which plants.
edit.
I think this is an example: Arisaema robustum f. atropurpureum T.Koyama in Ohwi, Fl. Japan, Rev. ed.: 300 (1965), nom. inval.
http://apps.kew.org/wcsp/named...