Perhaps one of the largest yellow trillium (Trillium luteum) I've ever found at the nature center.
As a general rule, all trillium are very slow growing perennial wildflowers, only producing one leaf—and not the characteristic three leaves—until roughly six years old.
In time, a single plant may produce two flowers, years later three, years later four, etc. This one has twelve which should mean that the parent plant is decades old.
As are most woodland wildflowers, trillium are fragile. Do not attempt to transplant. It's a death sentence for the delicate thing. Death. Death. Death.
They are also one of several plants that rely on ants to spread their seeds once they ripen in the fall. So if you want one in your yard, invite an ant to do the planting.