Ophioglossum vulgatum v O. azoricum

Ashley Basil and I have been looking at Ophioglossums in the New Forest with GPS locations provided by Alison Bolton

It is dificult to tell these small ferns apart and it seems that small O. vulgatum can look like O. azoricum
There are some useful pictures in the The illustrated field guide to ferns and allied plants of the British isles by Jermy, C. & Camus, J. on pages 21-23
I think it is instructive in order to identify these plants to dig them up and look at the structures below the ground
It seems to be fairly true that O. azoricum does come up in pairs whereas O. vulgatum does not