any of a genus (Trillium) of perennial plants of the lily family, having an erect stem that bears a whorl of three leaves and a single flower with three green sepals and three petals that change color as they mature
See trillium in American Heritage Dictionary 4
(trĭlˈē-əm)
noun
Any of various plants of the genus Trillium, of North America, the Himalaya Mountains, and eastern Asia, usually having a cluster of three leaves and a variously colored, three-petaled flower. Also called birthroot, wake-robin.