When this deciduous tropical tree is grown from seed, it will take three years or more to bloom. The seeds will cross-pollinate, so you aren’t guaranteed that the seed you collected from one specimen will bloom like it did. This is a long time to invest in a plant and not know if it will fit well in your landscape.
The dark purple-black growth that looks much like a thin eggplant is a Frangipani seedpod.
I have a few Frangipani volunteers growing in one bed right now, but had not seen the split seed pod before now. It looks more like a sculpture than seeds!
Due to the length to flower and cross-pollination of its seeds, I think this plant is best propagated from cuttings. The “cloned” plant bloom exactly like the parent. As I mentioned earlier, Frangipani has milky white sap. Allow at least a week for the cut end to dry before you plant it in dirt. Don't worry if you get busy or forget about it, the cutting will last a long, long time. Today I sent my daughter home to Austin with a couple of stems that have been scarring over since last fall.