B. 'Midnight Magic' (some sites have a similar one or the same one called Tita Corkscrew). I don't think it is classified as a rex but behaves like one with its affinity for mildew. Mine always comes down with a blight of mildew when I bring it into the basement for winter but a lot of begonias are like that. I usually cut off all the affected leaves and eventually start a spraying program. This is a begonia that is a survivor (not fussy like some).