Potato
Potatoes, root vegetables domesticated in the Andes mountains of South America, spread across the world before the collapse. While civilization practiced monoculture, breeding countless identical potato plants, collapse led to the rediscovery and spread of many traditional Andean varieties. Gardening communities across the Fifth World continue to grow and enjoy them, although the hotter and wetter climate means some communities have more difficulty growing them than others.
#Human relations
People of the Fifth World use potatoes for food much as people do now. They must always cook the potato to neutralize the toxins the raw tuber contains. Methods of preparation for the potato include boiling, mashing, and sticking in stews.
#Potato People
A community specializing in relationship with potatoes will invariably practice a certain amount horticulture, and therefore live in settled villages for at least part of the year. They may place such importance on potatoes due to living in a rocky, high-altitude, or soil-depleted region where other plants don't grow as easily. Such people may split their time between growing potatoes and hunting mountain-loving wild animals, such as sheep and goats.
A community specializing in relationship with potatoes will take great care to keep their potato crop genetically diverse, to protect against blight or dramatic weather. They may gather with their fellow potato-growing neighbors and trade for different varieties. A community may take particular pride in its own unique varieties, adapted perfectly to the specific microclimates in their territory. They will likely also use different varieties for different purposes, for example having one variety that they use for mashing, another they use for baking, and yet another that they think of primarily as medicine (due to its relatively high levels of antioxidants, e.g.).
A community specializing in relationship with potatoes may have developed that relationship in response to the Rusting Age. During that time, warlords rose up in many places to fill the niche left empty by fallen states. A local warlord may have demanded tribute from this community and the others around it. In response, this community may have determined that growing potatoes, rather than wheat or corn, could provide calories that the warlord's tax collectors couldn't see or collect as effectively. Long after a changing climate forced this community to practice more horticulture and less intensive agriculture, they may fondly remember how the potato helped them hide from the warlord until his empire, too, collapsed.
On the other hand, a community specializing in relationship with potatoes may trade that relationship back even longer. Regardless of where the community lives now, maybe their ancestors lived as peasants in Ireland, Eastern Europe, or other places where peasants ate mainly potatoes in the centuries after the Columbian Exchange. Or maybe they trace their relationship with potatoes all the way back to their beginning: to the Quechua and other indigenous peoples of the Andes mountains.
Towards the end of the Fourth World, it became popular to slice potatoes into long strips and deep-fry them. This method of preparation has become much more difficult in the Fifth World, but a community determined to preserve it can still do so -- with a good deal of work. Such devotion will require a community to maintain a certain infrastructure -- a clay oven in which to boil water, a pot to place inside of it, and a kind of mesh basket that can withstand the heat of boiling oil. They may have kept some of these things from the old world, lovingly keeping them in good working order, or found a way to craft what they needed from what they had around them. They will also need a large amount of fat (most likely animal fat). Because of this investment, a community may only deep-fry potatoes rarely, perhaps at an annual festival where many different communities can come together and enjoy the rare taste. Of course, once they have started deep-frying, they will likely not stop at potatoes, with festival-goers enjoying the challenge of frying anything and everything they can think of.