Question
can i propagate acacias and poincianas by cuttings or should it be by seeds? and how?

Answer
I would definitely suggest propagation with cuttings.

Simply cut a tender shoot that is at least six inches long. Remove the lower sets of leaves. Dip the cutting in a rooting compound. You can purchase this product at any garden center. Stick the cutting one inch into a good potting mix. Be sure to thoroughly wet the soil prior to planting.  Finally, cover the pot with a clear piece of lightweight plastic. Place the pot in indirect sunlight on an east window sill or under fluorescent lighting. After two weeks, check to see if the plant has rooted by slightly pulling on the stem. If you feel resistance, remove the plastic covering and be sure to keep the soil moist. The plant should then be treated as any other seedling.  

Please write again if I can ever be of assistance.  

Regards,  

Mike