Karpas

Question

With regard to using a banana for karpas, I saw that you quoted your father as saying "batlah daato etzel kok adam" I don't understand. Does he mean that most people don't regard a banana as a vegetable? But why is this significant -- if the berakahah is ha-adamah, why shouldn't it be good for karpas? Or does he meant that people coming to his seder will think he's crazy!