I always thought Potato was a seed. Accorrding to book I am reading by Steiner, it is a root.

Steiner: One thing you can see from this is that the science of the spirit we work with here recognizes the true nature of materialism. Materialism does not know anything about the world of matter; the science of the spirit recognizes the potato in particular as the real creator of materialism. . . . And people must clearly understand that if they eat too many potatoes their midbrain will wither away and it is even possible that their senses also suffer from eating too many potatoes.