I'll second Om's observation that it does just fine in full sun, if kept
watered.


I guess that's consistent with the fact that I hardly ever water mine!

But it really does thrive in the shade. I used to have periwinkles over
half the area, which were OK until fall, when they always declined. I
put some sprigs of Asiatic Jasmine in among them, and three years later
the periwinkles were gone and the jasmine had completely taken over.