Cassava
A woody shrub native to South America, cassava normally refers to this plant's starchy tuberous root. Prior to collapse, humans spread cassava across the tropical world. As the earth warmed, they brought different varieties into former temperate zones.
#Human usage
People who live in horticultural villages in the Fifth World frequently grow cassava as a staple food.
Cassava comes in both sweet and bitter varieties. Bitter cassava varieties deter pests, but contain more of the toxins that necessitate proper preparation of the root before eating. Horticulturalist communities will generally only eat bitter cassava in cases of food insecurity.
A person may simply cook sweet cassava to eliminate its toxins. But to make bitter cassava safe to eat, they must peel and grate the cassava root, then soak the gratings in water for four days to allow leaching and fermentation to take place, then cook it thoroughly (until soft). Boiling in water works well, but one must discard the water afterward.
People of the Fifth World make cassava into a wide variety of dishes, including breads and cakes (from cassava flour) and alcoholic beverages.
#Specialization
A community that specializes in relationship with cassava will invariably live in settled horticultural villages. They will likely practice slash-and-burn agriculture, growing different guilds of plants at different stages and moving around the jungle in a regular cycle. They will typically grow cassava in traditional "banana circles" with banana, lemongrass, sweet potato, and taro.