Alpiner, see if this helps:
http://www.marcellocatalano.com/indochina.html
Kevyn, is N. smilesii the only species that you're having problems with? Do you have a picture? If you know the plant's code, we can also know its origin, if it was from seed or if it was a clone (you can ask the code to your seller)... BE clones are selected for their vigour, while if it's a plant from seed you might have had some bad luck finding a weak individual... N. smilesii is a notoriously easy species to grow...