And that's only the plants themselves. Things get even more complicated when you look at recipes, when we have them at all (there is at least one Roman cookbook, for what it's worth). Pasta was not, perhaps, invented by the Chinese (that seems to be a fairly recent legend), but no one was eating spaghetti bolognese, back when the tomato was unknown less than five thousand miles from Bologna.
What does this have to do with writing, you wonder? Quite a lot, actually. Not everyone likes to describe food in fantasy (I've gotten through The Sign of the Sibyl without a meal more elaborate than "duck breast with rice, steamed greens, and wine"), but some go on at length. George R.R. Martin is a famous example, and there's a fair bit of food even in the Narnia books (Edmund and Turkish delight; Shasta eating butter for the first time; the three lords of Telmar at Ramandu's table).
Food, like clothing, weapons, armor, religious rituals, and government bureaucracies, can help set the feel of the fantasy story, that elusive element in world-building that lets you describe the setting and the characters and their customs in a series of swift strokes. Enough such strokes, and you have (if you're good at it) built up a picture of a whole imaginary world, or at least the parts of it that we as readers need to see. The kind of food you portray should thus fit the rest of the setting of the story, and give it the proper texture.
Food, like clothing, weapons, armor, religious rituals, and government bureaucracies, can help set the feel of the fantasy story, that elusive element in world-building that lets you describe the setting and the characters and their customs in a series of swift strokes. Enough such strokes, and you have (if you're good at it) built up a picture of a whole imaginary world, or at least the parts of it that we as readers need to see. The kind of food you portray should thus fit the rest of the setting of the story, and give it the proper texture.