Trillium sessile Linnaeus var. giganteum Hooker & Arnott, Bot. Beechey Voy., 402. 1840

Petals greenish white to deep red or purple, lacking any yellow pigments.

Flowering late winter--spring (late Feb--early or mid Apr). Variable habitat: edges, openings in and along ravines in redwood forest, thickets and tangles of cut-over forest, stream flats in deciduous woods, chaparral brushland, open wooded slopes on dunes, brushy islands in surprisingly open grasslands, but usually where soil remains moist most of the season; 0--600 m; Calif.

Trillium chloropetalum var. giganteum occurs in and around the San Francisco Bay region. The epithet “giganteum” is appropriate, considering this variety’s large size. In the populations that I have observed, it was more robust and generally larger than var. chloropetalum. Narrow-petaled forms of var. giganteum occasionally occur in mixed populations with the wider-petaled ones, and in a few places almost exclusively. J. D. Freeman (1975) suggested that these could represent the “undiluted” var. giganteum, free from influences of hybridization, as the type specimen has narrow petals.