Hi
Interesting plant in my area as it spreads like wildfire yet the hybrids type barely make a season Interestingly if I dig a hole or even lay mulch first thing that pops up is P. Always single and always white though the pink is short lived but will flower. SSome of the whites turn into shrubs and will flower for years . . Love the bi colored hybrids but have no luck at all. gary

There are some lovely cultivar colours but it's true, they often self-seed reverting to plainer colours, taller plants and smaller flowers.
The seed pods are longish and green, but turn brown pretty quickly and shed seed. I've attached a link to some nice closeups.
You can buy seed of distinctive colours - dark reds/purples and I've seen some "trailing" forms come out in nurseries here in Australia in the last few months.
I don't see why you can't try growing select forms from cuttings, probably semi-hardwood of older ones but why not try some tip cuttings in water as well and see how you go?

Here is a link that might be useful: scroll down for closeups of the seed pods

Thank you both, especially Alison. I think I now know why I have never seen any seeds. 1. the seed pod looks very like a flower bud. 2. I guess it's a bit like Busy Lizzie - as soon as it ripens it bursts open and scatters.
I've tried cuttings without success. i think they may need hormone. Will try again. - Ian.