Some additional information that might pin down the ID:
Stem is bristly, not smooth, and the color is pale green.
Leaves are opposite, except at the top of the stem where some are alternate.
Leaf feels flimsy, but very rough to the touch on upper surface, smooth and minutely-haired on under surface. A mature leaf is 7" long and 3" across at widest part. Where the leaf narrows towards the stalk, there are very slender strips of leaf continuing down the stalk to where it joins the stem.
I counted the petals on two flowers, one had 16 petals, the other 18.
Is there any other information that would help?
