I believe your begonia is B. fusca. Go to the International Database of Begoniaciae at this address:
ibegonias.filemakerstudio.com.au/browserecord.php?-action=browse&-recid=1951&-recnum=1&p=photo
This species is from Mexico - none I am aware of are from the Dominican Republic. It is classified as Rhizomatous, Giant Leaved, lobed. Leaves get to 12" or larger. If leaves do not get that large, let me know size and I'll try again.
