According to desert-tropicals.com, it's propagated mostly by cuttings.

If it's like the Dicliptera resupinata, it will make a few seeds right at the base of the flower in the "head". After the flowers wilt, protecting the flower head with a nylon mesh will keep the darned finches from eating the seeds.

I don't know how hard it is to germinate.

I've never even noticed seed on mine, or seen any self-seeding going on.

They are very easy to propogate by taking cuttings. If you're getting regular rain, you can just stick the cuttings into the ground and they'll generally root and take off. I've made a whole new bed of them this way.

BTW, I always cut mine way back in the spring, and any other time they're looking lanky. If yours get sun, you may not need to do much pruning, and you'll probably get more blooms than I do.