Potatoes

Solanum tuberosum is quite an amazing plant for agriculture. It's native to Chile/Peru (Inca lands), but can be grown in the wet marshlands of east Texas, the dry deserts of California, the high mountains of Japan, the hot African savannah, the freezing tundra of Siberia, and the grasslands of Ireland. Most other plants couldn't withstand that kind of climatic variation. It is nutritious and the natives describe its origins as a gift from their very gods. You could live for two weeks on it and a minor protein source like a swig of milk, albeit not well. And all but one part of it is utter poison.
I'm speaking, of course, of the common potato. Between it and milk, one would only be deficient in molybdenum, which can be supplemented back with a bit of oatmeal.
I think we should grow potatoes in space. Why? Practice. If we want to send a mission to Mars or farther, we'd either need three months of food packed and weighing down the whole mission (More weight needs more fuel), or we can grow our own en-route. And plants are an excellent absorber of carbon dioxide and other things we humans need filtered from the air.
I also think we should experiment with potato genetics. Potato blights have ruined many-a-harvest because the farmer was growing a monoculture that was all equally susceptible to the disease.