The Plateau of the Beheaded (断首台の丘) in the Demon World.
Mount Roraima in South America (tripoint of Venezuela, Guyana and Brazil).
I don't know if Togashi was inspired by Mount Roraima, but I think those mountain plateaus are very similar.
It also seems that the design of the Gargantuan Okunen Tree, where the Demon World Tournament preliminary matches took place, was inspired by some species of Dracaena (dragon tree):
Okunenju. Literally: Super Giant Plant・Billion-year-old Tree (超巨大植物・億年樹)
Let's not forget the famous Mimosa pudica (touch-me-not) from the Demon World used by Youko Kurama against Karasu. As he explained, it is a plant indigenous to South America. But Karasu was not interested in gardening T_T
Demon World's Mimosa pudica (魔界のオジギソウ)
Mimosa pudica. Their leaves fold inward and droop when touched, defending themselves from harm, and re-opening a few minutes later.