Answer: what potatoes and tomatoes share in common is that both are both (are related to nightshade).
Step-by-step explanation:
Both Tomatoes and potatoes belong to the same family called NIGHTSHADE. Nightshade is also called Solanum.
Potatoes are tubers which are harvested yearly. potatoes are actually the swollen part of the stem of the perennial Solanum tuberosum. As the potato plant grows, its compound leaves manufacture starch that is transferred to the ends of its underground stems (or stolons).
Tomatoes are fruits which are usually grown in the tropics as a perennial plant but in other areas it is mostly grown as a annual plant. Tomato is also a member of the genus Solanum within the family Solanaceae.
Although potatoes are tubers and tomatoes are fruits, the similarities between the two relate to genes that control important traits like disease resistance and metabolism.