If you are building a rain garden in the shade, consider the celandine poppy.
It does well in dappled shade, tolerates moist soil, and spreads by itself. It can tolerate drought, although it may stop blooming and go dormant. But it will be back the following year.
It has attractive yellow flowers that bloom in spring and early summer. The foliage is also attractive.
However, don't confuse the celandine poppy (sometimes called the woodland poppy), with the greater celandine. You can distinguish the two most easily by their seed pods.
The woodland poppy (Stylophorum diphyllum) is native, while the greater celandine (Chelidonium majus) is a pesky invasive species.
Another good plant for shady rain gardens is wild geranium--with a pretty purple flower.
More about celandine poppy
Info from the WI Master Gardener Program
Comments on the invasive greater celandine by Steve Glass
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