The Wood Poppy (Stylophorum diphyllum) is just starting to bloom in my large woodland garden. Its' yellow blooms light up my shade garden and it is hardy from Zone 3 to 10.
The flower is only partially open in this picture.
The flowers face upward when in full bloom, have four large petals and masses of stamens in the center. The leaves are large, deeply divided into lobed segments and grow from the base of the plant.
It will grow to a height of 1 1/2 feet tall in partial shade in a rich neutral to slightly acid soil. During periods of drought, the leaves may wither or turn yellow so mulching will help to retain moisture. The wood poppy readily self seeds, so you will have seedlings for transplant if you wish.
Although it is sometimes called celandine poppy, don't confuse it with the non-native and invasive celandine (Chelidonium majus), which looks very similar but behaves much more aggressively.
It will look wonderful combined with wild phlox (Phlox divaricata), white trillium (Trillium grandiflorum), twinleaf (Jeffersonia diphylla) or false Solomon's seal (Simlacina racemosa).
Consider it for your shade garden.