Tanacetum, is a genus in the aster family, Asteraceae, with a wide distribution around the northern hemisphere. They have finely divided leaves and the flowers can be composed of both disc and ray florets (T. coccineum) or just disc florets (T. vulgare)
Thalictrum, is a large genus of around 120-200 species in the buttercup family, Ranunculaceae, distributed around temperate regions. Their defining characteristics are finely divided leaves and flowers without petals, but with long colorful stamens in loose clusters. Some species have coloured sepals. They usually prefer moist soil and varying amounts of shade.
Trillium is a genus of 50 species in the family Melanthiaceae. This genus has been moved around quite a bit in recent years. It belonged to the lily family (Liliaceae) and when that family was divided, Trilliums were moved to the family Trilliaceae, which now has been combined with the Melanthiaceae family. They are woodland plants native to N-America and Asia and prefer part shade and fertile, moist, humus rich soil.
Trollius is a small genus of around 30 species in the buttercup family, Ranunculaceae, distributed around temperate regions in the northern hemisphere, the greatest number of species in Asia. They grow in moist soil in their native habitats, but can grow in any garden soils.