No-name begonias

Begonia 'Helen Teupel', sold unlabeled

In an online begonia group that I frequent, not a day goes by that somebody doesn't post one or more photos of begonias they got from a friend, or purchased without any label, asking "what is it?"  These are often rex hybrids, one of the groups I most often see offered without any names in garden centers.  There's something about rex begonias that seduces people into buying them, but there's apparently also something about them that makes people lose their names.

Begonias and temperature

Begonia sizemoreae (female flowers)

With temperatures dropping and the growing season coming to an end, I was going through some old photos for a blog post I'm putting together and came across some photos of a plant I no longer grow, Begonia sizemoreae.  This recently described species from northern Vietnam is closely related to B. rex (and according to some botanists the two belong to the same species).  I picked up this plant on a whim at a local begonia society show and grew it for a few years; while it didn't turn out to be the least bit hardy, it did give me some interesting hybrids that survived a couple of warm winters in the ground and encouraged me to attempt more crosses.