In reality, the arn were an artificially grown lifeform, and so had no actual birthplace. They believed, however, that they were born wild in birthing grounds and grew up in an idyllic woodland.
Using a metaphysical engine, Dorothea Ames, Quill and Ballon visited Arn Heaven on a mission to remove the arn from Quill's brain. Ballon needed the pheromones of an arn in order to carry out a successful operation. (TV: The Metaphysical Engine, or What Quill Did)