The green stalk sticking out of the center of each flower is the pistil - the female naughty bits of the Western Wallflower. The pistil accepts pollen through its tip and uses it to fertilize its ovules, which reside at the base of the pistil and will eventually become seeds.
The white stalks surrounding each pistil are the stamens - the male naughty bits. They produce pollen for insects to distribute to the pistils of other flowers. With any luck, they'll be other flowers of the same species, though the stamen will never know. Life isn't that great for the stamens.
This Photo: Along Highway 41 near Chinquapin (the Glacier Point Road turnoff), late May