Clematis: Jackmanii: 4 petals or 6 petals?, 0 by Rocco

Rocco wrote:
I posted a picture of my 'square' jackmanii earlier and now my second one is blooming. Most of the blooms have four petals like the earlier photo but a few of the blooms have five petals. The blooms with five petals are quite a bit larger than the ones with four petals. My two jackmanii plants have bloomed for many years but I have never seen five petal blooms on either one. It is possible that this plant has produced these blooms before and I had never noticed.