Key to the genera of Trilliaceae 1a. Inflorescence composed of tepals (if outer perianth segments are green; shape and size of inner and outer segments are similar); phyllotaxy trimerous TRILLIDIUM 1b. Inflorescence composed of sepals and petals (shape and size of inner and outer segments always dissimilar); phyllotaxy trimerous to numerous 2 2a. Sepals white, showy; petals filiform (to 1[-2] mm wide) or absent KINUGASA 2b. Sepals green or purplish; petals filiform to broad (0.1-6 cm wide), or absent 3 3a. Phyllotaxy mostly trimerous with leaves (0.8-) 5-15 (-25) cm wide; petals (2-) 7-15 (-60) cm wide (if narrower, petals either white or pink, or plants sessile-flowered) 5 3b. Phyllotaxy mostly 4- to 11-merous with leaves (0.8-) 2-5 (-7) cm wide (rarely to 60 cm with fewer leaves and height to 1m or more); petals filiform 1-2 (-3) mm wide (rarely 5-6 mm) 4 4a. Rhizome slender, running; seeds without aril PARIS 4b. Rhizome thick; seeds with enclosing red or orange sarcotesta, or partial green aril DAISWA 5a. Petals generally spotted, ovate, frequently appearing clawed, leaves cordate to rounded, coriaceous PSEUDOTRILLIUM 5b. Petals not spotted, from ovate to obovate, leaves ovate to obovate, "herbaceous" or not coriaceous TRILLIUM