Mudleaf

Source
3 mudleaf, in addition to 3 dizzyhead and 3 gloomberry, are required for the quest Swamp Bouquet, given by The Old Beldame, who is located in Swamp Witch's Hut.

You can pick mudleaf in Swamp Witch's Hut, or alternatively you can purchase them from Bokken at Oleg's Trading Post