In the Futurama episode "Mars University" the Professor implies that there are no jungles on Earth.
Fry: Wow! The jungles on Mars look just like the jungles on Earth!
Professor: Jungles? On Earth? (wheezing, old man laughter)
But, in the episode "Debate 3012", while Fry, Leela, and Bender are going to Chris Traver's birthplace, they are making their way through what looks to be a jungle. Leela slices through the vegetation with a large knife in both episodes.
Also, if there are no jungles on Earth, why? Is it due to pollution, dehydration, deforestation? Anything?
I don't know if jungles appear in any other episodes, or if it's just a rainforest, but I just noticed this a few days ago.