Maybe I'm just late to the party--I never heard of a perennial begonia until a couple of weeks ago at the garden center. My friend who works there and recommended it brought my skeptical self to her house where a thriving begonia that she planted last year (Zone 5/6) basked in the shade. I'm excited to see if my newly planted specimen returns next year. Here is an article about it from Brooklyn Botanic Garden: https://www.bbg.org/article/hardy-begonia-summer-blooms-and-wonderful-foliage-in-the-shade