Its British colonizers grew robusta and arabica, but much of that stopped during decades of conflict that forced people from their homes and made it hard to farm. Coffee trees require regular care such as pruning and weeding and take at least three years to yield fruit.

Catherine Bashiama runs her fingers along the branches of the coffee tree she's raised from a seedling, searching anxiously for its first fruit buds since she planted it three years ago. When she grasps the small cherries,

The bean native to South Sudan and a handful of other African countries has deep roots, thick leaves and big trunk help it thrive in extreme conditions where other coffees cannot.

Earth's warming climate is causing problems for big coffee producers everywhere and some are looking to excelsa, a rarely cultivated species that may stand up better to drought and heat. Excelsa is native to South Sudan and a handful of other African countries.