Sweet potato
The sweet potato plant grows as a flowering vine with a large tuberous root. The root varies in color, ranging from white to orange to red to purple. Originally domesticated in South America, Polynesians spread it across the Pacific Islands. Most adapted to historically tropical regions of North and South America, humans of the Fourth and Fifth World spread it further and further from the equator as the globe warmed. It flourishes all around the world, but rarely flowers in places that get less than 11 hours of sunlight.
#Human relations
People of the Fifth World enjoy the sweet potato tuber cooked in a wide variety of different ways: roasted, mashed, fried, and often mixed with a sweetener (such as honey) for a dessert. People also enjoy the young leaves and shoots as a nutritious vegetable.
People in South America often use red sweet potatoes and lime juice to dye cloth.
#Specialization
A community that specializes in relationship with sweet potatoes will invariably tend towards horticulture, and therefore live in settled villages at least part of the year. Often these communities practice swidden cultivation, growing different guilds of plants at different stages and moving around the jungle in a regular cycle. They likely grow sweet potatoes in traditional "banana circles" with banana, cassava, lemongrass, and taro.
A community specializing in relationship with sweet 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 tubers, 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 sweet potato helped them hide their food stores from the warlord until his empire, too, collapsed.
A community specializing in relationship with sweet potatoes may trace its ancestry to the Pacific Islanders who originally domesticated and spread the tuber. Or they may trace descent from sweet potato-loving people who once lived in the American Southeast. During collapse, as a result of climate change, the American Southeast and many small islands in the Pacific flooded, scattering these places' inhabitants across the world. They may still tell stories of how their ancestors fled the floods, taking care to bring sweet potatoes with them to plant in their new homes. The sweet potato, as a staple that kept their ancestors alive in difficult times, will likely hold great importance to them.