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Sunday - May 16, 2010

From: Johannesburg, MI
Region: Midwest
Topic: General Botany
Title: Trillium phototropism
Answered by: Damon Waitt

QUESTION:

I'm SURE you haven't had this question before. I live in northern Michigan in a wooded subdivision where we have clouds of wild grandiflorum trilliums growing in the woods on either side of the road. Today I noticed a four-petaled trillium, which got me searching the net. My question has to do with something else I've noticed. Every day, 90 percent of the trilliums on the RIGHT side of the road "face" the road. At the same time, 90 percent of the trilliums on the LEFT side of the road "face" the road. I've decided they must have some kind of sun-tracking mechanism like sunflowers. (Only, of course, the trilliums are not seeking the sun but the lighter area of the open road.) They do this in the early spring even when the trees are virtually leafless. The mechanism seems to "work" for trilliums far into the woods, not just those within ten feet of the road. Every year I marvel at this, but am stumped to explain it. Can you help?

ANSWER:

Regarding the four-petaled Trillium flower it is not unusual to find variation in the number of floral parts. This phenomenon results from developmental instabilibity and it casuses meristic variation (variation in the number of parts). Both environmental and genetic factors can cause a deviation from the normal number of floral parts and it occurs at a low level throughout the plant world.

Now for part two of your question. You are quite observant to notice the solar tracking behaviour of the Trillium flowers. This phenomenon is called phototropism (light seeking growth) and it is common in the genus Trillium.

From the Image Gallery

White wake-robin
Trillium grandiflorum

Red trillium
Trillium erectum

Painted trillium
Trillium undulatum