Petal Sepal Confusion

How do plants keep petals and sepals separate? I found a trillium (Trillium ovatum) that doesn't.

This is a trillium, its three originally white petals fading pink in late spring. The petals rest on three pointed green sepals. Below the flower are three large photosynthetic organs, which I just learned are technically not leaves, but bracts!

And this is a trillium that looks to have merged its petals and sepals into one structure. Huh.

Stormwater

With lady and maidenhair ferns, inside-out flower, and red huckleberry adding their chords to the growing symphony, the wood is really greening, but the canopy is still open.

Just before sunset of this very rainy day, the golden hour lit the woods vivid; the air was calm and sweet, but through the leprechaun scene a thick muddy snake rushed to the Willamette.

Gathering water from the streets and roofs farther up the hill, the small creeks swelled with runoff, gathered momentum, and thundered through the park. 

Chewing the bank at every turn, the rushing stream sculpted its channel. I could actually hear small rocks caught in the water slamming the insides of a metal culvert.