Trillium ovatum
(Pacific trillium, western trillium, western white trillium, western wakerobin)

The Pacific trillium (Trillium ovatum) brightens the early-season woodlands with distinctive, lily-like blooms.  As spring gradually creeps up the mountainsides, they emerge in succession at increasingly higher elevations until as late as August, rendering them a familiar sight for several months throughout their 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 sepals (the leaf-like strips that encase the petals before they open), and three petals, arranged in whorls up its stem.  (In rare instances, trilliums can bear these structures in multiples of more than three.)  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.

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.

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 scape, or, 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.  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.

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.

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.)

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.

Unusual Specimen

Below is an unusual example of what appear to be Pacific trilliums sporting 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.

© 2023 Anthony Colburn. Images may not be used or reproduced in any form without express written consent.


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