potato

yes,potato is kind of vegetable,in other words,all of the vegetable are plants.potato ia a kind of plant.so it is also a kind of vegetable.and the potato is consider as a root of the plant,other similar of the potato are: spinach; carrot; sweet potato.etc.

Yes, it is. The definition of a vegetable is not very scientific but rather traditional. The following is a list of vegetable from wiki and as you can see, potato is one of them:
http://en.wikipedia.org/wiki/List_of_vegetables

Yes, potato is a kind of vegetable.