The crop that provided nourishment to the growing population of Europe and eventually led to tragedy in Ireland when people became overly dependent on it was Potatoes. During their time period, they didn't have anything else to grow in their farms, until their discovered potatoes. Potatoes was one of the main crops they grew to help feed them. Because it helped feed them, it allowed for them to grow their population because they have a food source that can keep them full without worrying about starvation. In Ireland, they depended on it too much, the only thing they ate was potatoes, and that was it. As soon as something happens to the production of potatoes, they would all freak out because it is one of the things they thought they needed to survive, and that's what caused the tragedy in Ireland because they couldn't get more potatoes. They evolved around potatoes and depended on it way too much, when there were other sources to nourish their hunger