Uthe 3

Uthe 3 was a planet once visited by the Fourth Doctor, Romana II and K9 Mark II. When they landed there, they found a world that was lush with vegetation, but whose population was living in underground bunkers. The Uthians believed that they were still in a state of war, and that the surface was uninhabitable due to Rad-Plague contamination. They believed this not because they had actually visited the surface, but because they merely accepted the word of their battle computer. The Doctor was able to free the people from their misconceptions by showing the computer a Uthanian scatterbud, a flower that grew uniquely on Uthe 3. Once the computer's logic was successfully disputed, the people began to repopulate the planet's surface.

The name of the planet was, according to the Doctor, pronounced like youth. (PROSE: Sweet Flower of Uthe)

Behind the scenes
The story indicates two demonyms for Uthe: Uthian for the people and Uthanian for the flower.