Glabrous erect unbranched herbs, with short scarred rootstocks and 3 leaves whorled at the summit of the stem, subtending the sessile or peduncled solitary bractless flower. Solitary long-petioled leaves are sometimes borne on the rootstock. Perianth of 2 distinct series of segments, the outer 3 (sepals) green, persistent, the inner 3 (petals) white, pink, purple or sometimes greenish, deciduous or withering. Stamens 6, hypogynous; filaments short; anthers linear, mostly introrse. Ovary sessile, 3-6-angled or lobed, 3-celled; ovules several or numerous in each cavity; styles 3, stigmatic along the inner side. Berry many-seeded. Seeds horizontal. [Latin, in allusion to the 3-parted flowers and the 3 leaves.]

About 24 species of North America and Asia. Besides the following, some 7 others occur in southern and western North America. Known as Three-leaved Nightshade and Birthroot. Phyllody, i. e., the reversion of petals or sepals to leaves, is occasional, and the floral parts are sometimes in 4's. Type species: Trillium cernuum L.