The Pacific trillium (Trillium ovatum) brightens the early-season woodlands with distinctive, lily-like blooms. As spring gradually creeps up the mountainsides, it emerges in succession at increasingly higher elevations until as late as August, rendering it a familiar sight for several months throughout its range. As its name suggests, each trillium (literally, “tri-lily”) consists of exactly three bracts1Bracts are leaves that occur within or just below a flower cluster and often differ in size, form, and sometimes color from ordinary leaves., three sepals2Sepals are modified leaves that enclose a flower bud before it opens and are usually green., three petals, and three stigmas3A stigma is the organ at the tip of a flower’s female reproductive structure that receives pollen. It is typically connected to the ovary by a style. These three parts together comprise the pistil.. These are topped by a ring of six anthers.4An anther is a floral organ that produces pollen that contains a plant’s male reproductive cells. Together with the filament that attaches it to the flower, it comprises a stamen. (In rare instances, trilliums can bear these structures in multiples of more than three, in which case the anther count typically doubles that of the other components. See “Unusual Specimens” below for an example.) Botanists disagree on whether and where trilliums fall within the Liliaceae family or broader Liliales order, but it appears that they are only distantly related to the true lilies of the genus Lilium, despite their similarities.
Blooms
Pacific trillium blooms are variable in form and color. They typically face somewhat sideways in the direction of their light source, but can range from upright to dangling. The petals can be nearly oval, broadly triangular, or elongated and almost ribbon-like. Trillium scent, too, can range from sweet to pungently unpleasant, possibly an evolutionary attempt at attracting a diversity of pollinators, which are known to include bees, beetles, and moths. The most dramatic variation among trilliums is the transformation a single bloom can undergo as it ages, when it can fade from flawless white to shell pink, purple, or near red. This transition is thought to result from pollination and may serve as a subtle suggestion that pollinators go elsewhere for a treat, although many trilliums wither and go to seed without any significant color change. The incidence and intensity of color change appears to vary by population or location. Finally, the intricately veined texture of the petals, pleasing at any stage, also becomes more prominent as the bloom matures.
Plant Features
Given their unique structure, trilliums are a study in botanical terminology. They are perennials that sprout each year from rhizomes, which are thickened underground stems. Their unusual form is due in part to the fact that each trillium is not a “complete” plant, but rather only a scape5A scape is an inflorescence that rises from the ground with no or only basal leaves., or, leafless flower stalk. What appear to be leaves are actually leaf-like bracts that many plants use to protect flower buds as they develop. In the trillium’s case, the bracts enfold the delicate bloom as it emerges from the ground and then fan into a whorl at the base of its pedicel6A pedicel is the stem that connects an individual flower to the larger inflorescence.. In most plants, bracts are small and scale-like, but in trilliums, they have enlarged to such a size that they double as leaves for photosynthesis. In true evolutionary efficiency, no other components are needed. Of course, efficiency comes at a cost: if those three bracts are damaged or removed, the trillium’s ability to nourish itself through photosynthesis for the rest of the year is seriously impacted, as each rhizome typically grows only one scape per season. For this reason, trilliums should never be cut or picked.
Seed Capsules and Distribution
Even trillium seed dispersal is fascinating. Trillium fruits are ribbed, berry-like capsules, from which a number of seeds scatter — or are carried — when the capsules ripen and split open or are eaten. Trilliums are one of many plants that produce seeds that have fatty, external structures called elaiosomes, which seem to have the specific purpose of attracting ants and a few other insects and arachnids. Ants carry the seeds to their nests to eat the nutritious elaiosomes, after which they discard the seeds on their subterranean waste piles, where the seeds germinate in the fertile, well-aerated organic matter. Deer, too, love all parts of the trillium, and especially the seed capsules. Because the seeds can survive the trip through a deer’s digestive tract, they find new and fertile ground at the other end. This is thought to have contributed to the many trillium species’ broad distribution across North America after the last ice age, farther than the tiny legs of ants alone could have borne them in that time.
Range and Habitat
The Pacific trillium ranges throughout moist woodlands of the Pacific and Salish coasts from British Columbia to northern California and eastward into the Rocky Mountains. It is typically associated with conifer forest, but is also found in mixed woodland. (Note the specimen circled in the accompanying habitat photo.)
Subspecies and Other Species
The Pacific trillium is distinguished from other Western Washington trilliums by having solid-color bracts with no markings and by having a short pedicel (an individual flower stem) between the leaf bracts and the flower. (Other species are sessile, or, stemless, with the flower cupped directly in the juncture of the bracts, which are themselves sessile.) There are three quite similar varieties of the Pacific trillium, but only one, T. ovatum var. ovatum, grows in Western Washington, where all shown here were photographed.
The Pacific trillium bears a superficial resemblance to the vanillaleaf (Achlys triphylla), which also features tri-part leaves and shares the trillium’s range and habitat. However, the trillium can be distinguished by its entire (undivided and untoothed) bracts that always end in a point, unlike broad-ended, scalloped, and sometimes divided leaflets of the vanillaleaf. The trillium also produces a single bloom from the axil of its leaf bracts, whereas the vanillaleaf bears a cluster of multiple small flowers on a separate leafless scape. Finally, the bracts of the trillium do not exude a notable scent upon withering, as does the foliage of the vanillaleaf.
Gallery
Unusual Specimens
The accompanying photo features an unusual example of what appear to be two Pacific trilliums displaying enlarged, veiny sepals much more like leaf bracts than ordinary sepals. The blooms also appear correspondingly smaller. No nearby specimens were observed with this variation and the phenomenon does not appear consistent with any known species or variety of trillium in Western Washington. It is perhaps the result of a very localized mutation or infection.
As noted above, Pacific trilliums sometimes form with parts of greater than three each. The “pentillium” below sports nearly five complete leaf bracts and petals and nine anthers. (The tenth anther appears fused with the malformed petal.) No other nearby trilliums were observed with irregular numbers of components.
© 2023 Anthony Colburn. Images may not be used or reproduced in any form without express written consent.