Cats have an exceptionally acute sense of smell/taste (also known as the vomeronasal organ). The floor licking is an example of this: something at that site is causing the licking, and you or me will never know the source unless the previous tenant enlightens us. Even washing the spot many times may not remove the mark.
Getting rid of a potentionally toxic plant is wise. When acquiring plants in the future, ask if they are animal friendly; always research the type of plant if you are not certain.
And while I don't think the plant caused the licking manifestation, I do believe that the plant could possibly have impacted your cat's appetite. Once the plant is gone, monitor your cat's appetite. Hard to say if your cat likes apartment living, but try to make it comfortable--lots of interesting quiet places to hide, give lots of attention and affection, allow for stimulation (a window seat is always a favorite spot from which to watch the world.)
Dr. Van Lienden
Dr. Raymond Van Lienden DVM
The Animal Clinic of Clifton
12702 Chapel Road, Clifton
Virginia, U.S.A. 20124