Cyrodiil is the largest province in Tamriel, stretching 2/3rds of the way across the continent both east-west and north-south. It should never have been described as a single biome, and jungles couldn't possibly exist in most of its terrain, but it was a mistake for Oblivion not to include jungles in the sections that should have had a warmer clime. Of course, Oblivion in general was hopelessly generic, re-using the same meadows, rolling hills, and forests across the vast territory of the Imperial Province rather than even managing to replicate the ecological diversity that Morrowind demonstrated just in the island of Vvardenfell, much less the greater variety that should have existed in the vast area of Cyrodiil.
