I've been playing so much AC lately I started calling them turnips today too!
Parsnips are LOVED by Pam if you are working on trying to boost friendship with her. I like the gifts she sends me. Early game batteries, yes, please.
They are very gold efficient for energy in the early game. One parsnip sells for 35 gold or can be eaten for 25 energy. Normally, anything better than a 2 to 1 ratio gold-energy is more efficient to eat for energy than sell, assuming you need the energy.