Today I saw this little plant flowering in my garden.  I have no recollection of planting it (although that doesn't mean that I didn...

For the four years since I moved here, I've been wondering what this plant was that I inherited. It's planted next to my pond, ...

Can anyone help identify this plant?  It's appeared in a very shady spot in the garden, and I have no recollection at all of planting an...