Tropicals & Tender Perennials: Can anybody help me identifying a tropical plant ?, 1 by bonitin

bonitin wrote:
Thank you for your respons Moodene and Erick.
Here some more information: it has a strong quadrangular stem, the leaves are implanted opposite and make new shoots in the inter nodes. Originaly it has tendency to grow bush-like, but I trained it to grow with one single stem, in order to save place, as I have so many babies to take care of and lack of space.
I send another picture of the underside of the leave which is grayish green. Hope that might help to identify it.