A genus of about 50 species, of e. North America, w. North America, and e. Asia (especially se. North America). The genus Trillium in our area is difficult and complex. Trillium is now usually separated from the Liliaceae (along with Eurasian genera such as Paris into the Trilliaceae (Zomlefer 1996, Kato et al. 1995, Kawano & Kato 1995, and others) or less drastically as part of the Melanthiaceae (Chase et al. 2000; Tamura et al. 2004). The subgeneric classification of the genus follows Lampley et al. (2022).
ID notes: Teratological forms are frequent in some species, as, for instance, leaves, sepals, and stamens in 2's or 4's, petals sepaloid, or sepals petaloid, and so forth. What are called “leaves” in Trillium are actually interpreted as bracts by some. Most species are slow-growing perennials; seedlings, juveniles, and depauperate or "tired" plants are one-leaved ("monilliums"), recognizable by the similar color, texture and venation of the single leaf to the three leaves of mature plants. In some species, such as Trillidium undulatum and taxa of the Trillium pusillum complex, individual plants remain in the single-leaf stage for long periods of time, and populations may consist largely of juvenile plants.
Ref: Bodkin & Reveal (1982); Bodkin & Reveal (1983); Case (2002) In Flora of North America Editorial Committee (2002a); Case & Case (1997); Chase et al. (2000); Farmer & Schilling (2002); Freeman (1975); Gaddy (2008); Kato et al. (1995); Kawano & Kato (1995); Lampley (2021); Lampley et al. (2022); Mitchell (1990); Patrick (1986); Patrick (1989) In Wofford (1989); Patrick (2007); Schilling et al. (2017); Schilling et al. (2019a); Schilling, Floden, & Farmer (2013); Tamura et al. (2004); Tamura In Kubitzki (1998a); Timmerman-Erskine, Dute, & Boyd (2002); Zomlefer (1996). Show full citations.