I'm a newbie as well, and my knowledge on this subject is based only on observations of my own Jackmanii. The first year I planted my vine, I only had 4 petal flowers. Now in the vine's 3'rd year, it has produced both 4 petal, and 5 petal flowers ( and it has grown tremendously since it's first year as one scraggly looking vine, each year it comes back MUCH fuller than before. When I first adopted my clematis I thought maybe I would need to buy more than one plant for it to fill out the way I had hoped...ha ha). So, my very unscientific guess would be that age/maturity has a factor in the size of the flower/number of petals.
Heidi
7bDigitalV>I bought a Polish Spirit. The only difference I noted between a
Jackmanii and the Polish Spirit is that the Jackmanii photos always
>seemed to have four petals and PS had five. I've read that J. can have
>4-6. I also understand the PS is clasified as a J.
>
>The clematis I have has over 15 flowers but all have four petals.
>Is the number of petals 4 vs 5 vs 6 controlled by variety or
>environmental/fertilizer. I actually prefer the fuller look of a five
>or six petalled one.
>
>Sooo... is there a variety that tends to have more petals. Is if just
>a random thing? More petals when the plant is well established?
>
>
>DiGiTAL ViNYL (no email)
>Zone 6b/7, Westchester Co, NY, 1 mile off L.I.Sound
>1st Year Gardener
>
>