Italian Girl -

yes you can - by depositing pollen from one flower on the pistil of another. It will take you long time and you will get tons of small seeds that will take 6 months to grow so the look as Nematanthus again.

If you want to cross different varieties and get some interesting new babies - it is a noble cause.

If you want to get more plants of the same type - take cuttings and stick them in a loose humid soil - they root very fast.

Good Luck

Irina