I would LOVE anyone's help identifying this plant! I've had it for 5 years, and absolutely love it, but have no idea what it is! I tried to capture scale well, but may have failed. Large mature leaves can reach 25 - 30 cm at their widest points, and the petiole supporting each leaf can be 40 to 50 cm long. When well watered, the plant holds the leaves up, straight out towards the light. Flowers are white with pink near the edge of the petals. Grows REMARKABLY fast!
A HUGE thank you to all three of you! Using the answers you provided, I searched the internet and looked at pics from the various names you entered, ultimately the search querry (google) was "begonia rex alba". Third link down, "Tropical Plant List B" at glasshouseworks.com lead to a list of specimens with common names. Fourth or fifth one down "Begonia Immense" looked very similar. Google Images search for "Begonia Immense" produced many images from various sources that are very similar to identical with mine, at least to my untrained eye. So what would the latin name be? Begonia alba, rex variety? Thank you so much!
If it's a hybrid cultivar 'Immense' then that would be the entire second part of the name. Or if it's a species B. immense, then same situation.