Polypodium vulgare dimorphic?

I noticed that Polypodium vulgare, which I saw in Denmark, seems to develop two distinct types of fronds. (1) Some have a somewhat triangular outline with slightly curved pinnae, while (2) others show a more rounded arrangement, with the pinnae extending almost orthogonally from the central vein. The second type lacks pinnation at the tip and has an elongated “central” pinnae (see 2nd image, not taken of this plant though), whereas the first type does.

This photo isn’t very representative. I should have taken a comparative image while I was still there.

I initially thought this fern might be dimorphic, but both frond types can bear sporangia, and according to the internet it is not considered dimorphic.

Does anybody why? I’m intrigued.