Plant of the Week
Decumbent Trillium (Trillium decumbens)
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 aboveground 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.
The decumbent trillium is one of the sessile trilliums and is very similar in appearance to the more common Trillium cuneatum with the exception that upon first glance it seems to have no above ground “stem”. The rhizome of this species is often “s” shaped, arising from the ground several inches from where the leaves lay flat on the ground surface. Known only from a limited range in Alabama, Georgia, and Tennessee, this species often appears to have been “plucked” from its stem and laid flat on the ground along the side of a trail. Decumbent trillium typically blooms from mid-March through April and is found in mature deciduous woodlands or on thin, open rocky wooded slopes, adjacent to and along stream floodplains.
For More Information
- PLANTS Profile - Trillium decumbens, decumbent trillium
- Flora of North America: Trillium decumbens
- Case, F.W., R.B. Case. 1997. Trilliums, Timber Press, Portland, OR.