The Red Willow is a tree that appeared in The Monster and the Willow.
Red Willows grew in the back of the Island Turtle. Most of the willows looked like normal trees and grew in a spiral shape around their leader so that the free spaces between them formed a path leading anyone who landed on the turtle's back to the leader tree.
When the Winx went to the Black Mud Swamp after Flora moved there to prepare for her exams and find the Cheerful Gladiolus, they met the Water Nymphs who told them that there was an enormous monster in the Swamp which threatened them. The Nymphs explained to the Winx that they needed a plant called Zilith which they used to make their homes, and that it grew on an island at the center of the Swamp, but that the monster was a constant danger to them. So a nymph would sometimes volunteer to go to the island and pick Zilith leaves and shortly before the Winx went to the Swamp a nymph named Luzis went to pick some Zilith but she never came back.
The Winx decided to fight the monster, but it captured Musa and the Winx had to go underwater to save her. After saving Musa, the Winx landed on the island and went towards the Leader Red Willow. They nearly all fell asleep there except Tecna who found out that the Leader tree was giving off sleeping gas and created a bubble which woke Bloom up. And made the other Winx girls woke up. The Winx then made the bubble bigger and awoke Lusiz who had been in constant telepathic contact with the environment surrounding her and found the truth about the monster. She explained them that there was actually no monster but that in fact it was a giant sleeping and sleepwalking turtle which was asleep because of the Willow's gas and that when it moved in its sleep.
The Leader Willow then tried attacking the Winx but it was finally defeated by Bloom and Flora and the turtle moved away after letting the Water Nymphs picking Zilith leaves from its back. But the Nymphs only had some leaves and Flora used her rapid-growth formula to make more Zilith plants grow for the Nymphs, who gave her the Cheerful Gladiolus as a present.
The Leader Red Willow tree gives off sleeping gas that makes the nearby living creatures asleep.