The Holy Greens
Scattered across the world are 13 Holy Greens, centered upon one of the Green Mothers. Most of them are habitable, the lone exception being Green 13.
Each Green is essentially an independent city-state that is self-governed. For the most part they are autonomous, but each Green is heavily influenced by the Church. Leaders must be sanctioned by the Church, and leaders who ignore the word of the Church face sanctions and even excommunication or exile.
The size and population of each Green is typically dependent on the age of the Green Mother. As the oldest, Green One is several hundred miles in diameter, and hosts a population of several hundred thousand. Green 12, the youngest populated Green, only hosts a population of several thousand and stretches a mere 120 miles from end to end.
Green 13 is an anomaly. At only 16 years old, it already sports a size roughly equal to Green 1. The Green is also largely inhospitable, full of dangerous flora and fauna. Several expeditions have attempted to explore the Green, and all have failed.