Yellow Pimpernel

Yellow Pimpernel

Observation - Yellow Pimpernel - UK and Ireland. Description: Low growing plant with yellow flowers normally with 5 petals. How unusual is it to see a 6 petal version, there are at least two in the main picture but I can't see any on Google images?

Low growing plant with yellow flowers normally with 5 petals.
How unusual is it to see a 6 petal version, there are at least two in the main picture but I can't see any on Google images?