Maybe carthusiana this time?
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I believe that the pale scales are fairly reliable on mature fronds, especially when you combine this with the growth form and the erect, not arching, leaves.
The hybrid is not that common. I went in search of it last autumn in a dry wood. I picked a leaf from 15 Dryopteris carthusiana plants and 15 from D. dilitata plants, while particularly looking for intermediates. All leaves proved to be fertile with abundant spores.
"I believe that the pale scales are fairly reliable on mature fronds, especially when you combine this with the growth form and the erect, not arching, leaves."
Yes, I agree, though I raised the issue previously as the then posted photograph wasn't necessarily a mature frond. I also agree the present photograph is indeed carthusiana.
Yes, I have sometimes searched mixed colonies of the parents and failed to find any hybrids, but in other locations, usually damp, degraded woodland, edges of forestry plantations or after drainage, I may find large populations of the hybrid and little or no carthusiana - very much the situations described by Chris Page in his ferns book. In my own vice-county (Wigtownshire) I see more of the hybrid than D. carthusiana, but that may be a disinclination on my part to get my feet wet. D. carthusiana is quite good at hiding in longer vegetation.
All comments much appreciated - very helpful.
Lat/Lng: 52.2, -1.6
OS grid ref: SP3059