Plant of the Week
Western White Trillium (Trillium ovatum var. ovatum)
By Mark Pistrang
All trillium species belong to the Liliaceae (lily) family and are rhizomatous herbs with unbranched stems. Trillium plants produce no true leaves or stems above ground. The “stem” is actually just an extension of the horizontal rhizome and produces tiny, scalelike leaves (cataphylls). The above-ground plant is technically a flowering scape, and the leaf-like structures are actually bracts subtending the flower. Despite their morphological origins, the bracts have external and internal structure similar to that of a leaf, function in photosynthesis, and most authors refer to them as leaves.
Trilliums are generally divided into two major groups: The pedicellate and sessile trilliums. In the pedicillate trilliums, either the flower sits upon a pedicel that extends from the whorl of bracts, “erect” above the bracts, or “nodding” recurved under the bracts. In the sessile trilliums there is no pedicel and the flower appears to arise directly from the bracts.
Western white trillium falls within the pedicillate group of trilliums, sporting a large white flower above the leaves that often changes to pink, purple, and even red with age! Flowers are typically seen from late February through April in coniferous and mixed coniferous-deciduous forests, alder thickets, and shrubby areas. Known from the Pacific Northwest, south to California, and inland to Idaho, Montana, and Wyoming, the western white trillium is the most widespread trillium in the western states.
For More Information
- PLANTS Profile - Trillium ovatum var. ovatum, Western white trillium
- Trillium ovatum var. ovatum in Flora North America
- Case, F.W., R.B. Case. 1997. Trilliums. Timber Press, Portland, OR.