I don't know much about this Begonia - beyond that it is a species originally from China and came with the designation "b09". I seems VERY closely related to B. debaoensis, if not that species. The more i grow this, the more i'm quite convinced this is an example of that species. It even bears the distinguished single petal female flowers.
It is a fairly slow grower for me. Growth habit is quite flat to the media, and has a slowly creeping horizontal rhizome (with short-ish internodes between leaves). The foliage is heavily textured / almost corrugated. More details can be seen in the attached photos.
I grow it as a terrarium subject - very carefully watered so as not to keep it too wet.
Offered here as husky plants in 2 1/2-3" pots.
View Terrarium / Begonia Culture Sheet