It never shocks me to learn that a colleague of mine has been misinformed about the true classification of the potato. The potato is in fact a legume. A legume is plant that is able to fix nitrogen from the air and put it into the soil. A colleague of mine informed me that a potato is a plant that can do this. thus, it is classified as a legume, not as a vegetable. The following source, Godsfried's Dictionary correctly defines the potato as a legume.