This beautiful Begonia is from Ecuador, and is a IUCN threatened species. For me it has reached about 8″ tall, but it seems possible it could get taller with better care. I have mine growing in 100% clay, which it is liking overall, but sometimes goes through melting spells when it gets too large and the leaves come in contact with the surrounding plants and wood features of the terrarium. It does not like standing water on its leaves and should be treated with care, any rotting leaves should be removed promptly.
A different clone below, with no speckling and a slightly bluer, thicker, leaf.