Giant Trillium (T. chloropetalum), AKA giant wakerobin (!), has three leaves, three sepals, & three petals: three times three, a trillium. Wikipedia says that what look like leaves here are actually bracts, and the trillia have "no true aboveground leaves" (Trillium, 3/2016). These do look like leaves to me, even given their nice patterns.
Trillium are one of my favorite flowers. Thanks to Jerry Hearn for alerting me to the prolific trillium on Trail 2 at Jasper Ridge. If you want to see trillium at Jasper Ridge, Trail 2 is a good place, and now is a good time. Just watch out for poison oak.