Woodland Plants: The Trillium
By Darcie McKelvey
One of the most familiar and beloved woodland wildflowers is the trillium. Most botanists believe that the trillium belongs to a separate family of plants called Trilliaceae. Its close relatives are the genus Paris and Trillidium, neither of which is native to North America. Five or six species of trillium are found in eastern Asia, seven species in western North America and 35 species in eastern North America.

Ontario is blessed with several different species of trillium, including Ontario’s provincial flower, the great white-flowered trillium (Trillium grandiflorum or “large-flowered” trillium). There is a certain simplistic elegance in three whorled leaves with a three-petaled flower (arising from the centre of the leaves). Trilliums grow from an underground rhizome, which often lies horizontally under the ground. Masses of roots extend downward from the rhizome.
Trillium grandiflorum (large-flowered trillium). Photo courtesy of Patrick Bunting.

Trillium grandiflorum is the showiest of all trilliums worldwide and is highly prized in Europe and Japan. It blooms in late April to early June. It opens after Trillium erectum, when the two are found together. The flowers are white, but fade to pink as it ages. It prefers well-drained soils in deciduous woods, particularly mature sugar maple and beech forests. Very rarely the flowers will be pink upon first blooming; this variation is called Trillium grandiflorum f. roseum.

Trillium cernuum (nodding trillium) has a smaller lavender-grey coloured flower, and the pedicel or stem is curved downward so that the flower is usually hidden. It prefers moist to swampy woodlands and is sometimes found with Canadian yew (Taxus canadensis).

Trillium erectum, or red trillium is also known as wake-robin, stinking Benjamin and Beth root. The flowers are dark maroon and usually appear in late April and May. This trillium prefers a more acid soil than Trillium grandiflorum. It is found in upland deciduous forests or mixed white pine deciduous forests. This trillium sometimes hybridizes with Trillium cernuum and a white variant has also been found.

Trillium undulatum or painted trillium requires a deep humus (6 inches or more), strongly acid (pH of 4-5), cool (e.g. shaded) soil. This is the most difficult eastern trillium to cultivate and the latest to bloom. Flower petals are narrower and are white coloured with red marks in the shape of the letter “V” in the centre. This species of trillium is generally found in second growth red maple (moist sites), birch and oak forests close to old white pine stumps.

Sometimes mutant plants with green striped petals are found in the Trillium grandiflorum species. These plants are diseased -- infected with parasitic mycoplasmas that cause the greening. As time passes, the mycoplasmas will cause deformity in the petals and eventually the death of the plant. Although sometimes erroneously prized for this aberrant colouring, these trilliums should be removed before the mycoplasmas can spread to affect an entire colony.

Cultivation of trilliums is slow, requiring seven years at a minimum from seed to flowering. Flowers are pollinated by ants, flies and beetles. The seeds are hydrophilic, requiring consistently moist conditions if they are to survive. The seeds do not germinate readily and can remain viable for many years provided they are in moist soil. Once the seed germinates, the first year’s focus is on the roots only. In its second year, the seedling will produce a single seed leaf. In the third year, the first true leaf will appear. Two or more additional years will be required before the plant produces the three-whorled leaves that we are familiar with.

Trilliums are sensitive to light and full sun exposure is detrimental. For this reason, selective lumber harvesting will not destroy a trillium colony, but clear-cutting will. Trillium flowers are a favourite source of food for deer, and repeated grazing will kill the plants.

Picking a trillium flower does not necessarily kill the plant, which depends on the green leaves for photosynthesis. Usually the pedicel or flower stem is fairly short, and damage will result if the green leaves are taken as well. The leaves cannot regenerate until the following year and this may not happen at all depending on the size of the rhizome.

The absolutely best book on trilliums is written by Frederick W. Case, Jr. and Roberta B. Case and is entitled Trilliums, (ISBN: 0-88192-374-5). It is very readable even though authoritative, and the pictures of the various species are breathtaking.

About the author: Darcie McKelvey is a native plant enthusiast who considers her entire 10-acre woodland to be a garden.

This article appeared in the Summer/Fall/ 2005 (Volume 40) edition of the S&W Report the newsletter of the Ontario Woodlot Association.

© Ontario Woodlot Association