Key to the subgenera of Trillium 1 Flowers usually pedicellate; leaf uniformly green, usually not mottled ............................................................................................ 2 - Flowers sessile; leaf green usually with darker shades of green and silver mottling scattered over the surface4. T. subgen. Sessilia 2 Stigmas uniform (not tapered), united in a common style or at least basally connate; ovary at anthesis somewhat obscured by corolla and stamens and relatively less exserted, 3- or 6-angled, typically white, greenish white or green; petal with margins undulate, basally overlapping, pink or white aging to various pink shades or remaining white (T. nivale); adaxial petal venation not engraved; flower funnelform or at least with basally erect petals shallowly encircling ovary; leaf ovate, elliptic-ovate, ovaterhombic, ovate-lanceolate or oblong .................................................................................................................................................. 3 - Stigmas thicker basally and tapered above, separate; ovary at anthesis exposed, exserted or only slightly obscured, typically strongly 6-angled or ridged, generally dark red, to creamy white or white with red markings; petal with margins entire, separate or only slightly overlapping, if white, aging to brown; adaxial petal venation typically engraved; flower open, or widely agape, not funnelform; leaf shape rhombic, broadly elliptic, rhombic-ovate or lanceolate-elliptic (T. hibbersonii) ..........1. T. subgen. Trillium 3 Stigmas connate; leaf elliptic-ovate, ovate-lanceolate or oblong.................................................................. 3. T. subgen. Delostylis - Stigmas only basally connate; leaf ovate, elliptic-ovate or ovate-rhombic................................................ 2. T. subgen. Callipetalon

Published as part of Lampley, Jayne A., Gereau, Roy, Floden, Aaron & Schilling, Edward E., 2022, A revised subgeneric classification of Trillium (Parideae, Melanthiaceae), pp. 278-286 in Phytotaxa 552 (5) on page 280, DOI: 10.11646/phytotaxa.552.5.1, http://zenodo.org/record/6796567