"This is the portal between the flower garden in Toad Town and Flower Fields. The Wise Wisterwood, who's the elder of this fair land, watches over the area. Talk about a big tree!"
Flower Fields is a location in Paper Mario. After Mario had obtained the four Magical Seeds, Minh T. was able to plant the seeds in the Toad Town garden, which opened up the portal to Flower Fields. When Mario first entered through the portal, the door was connected to a large tree, Wise Wisterwood, which told Mario of the current state of the once peaceful and beautiful fields. A cloud-being named Huff N. Puff was said to have created dark clouds that covered the sky, which caused the Sun to have fallen out of it and to be holding a Star Spirit captive. In order to get to Master Huff N. Puff's hideaway on Cloudy Climb, Mario had to grow a seed that stretched all the way to the heavens. In order to do so, he needed to obtain the Magic Bean from Petunia, some Miracle Water from Lily, and some Fertile Soil from Posie.
It's the only area of the game without a Heart Block or a Toad House. There's also a flower called Tolielip here.