- Dear William,
So sorry to be so late in my reply. As usual, I'm up to the eyeballs - with Trichomanes speciosum at the moment.
Yes, Dick Roberts did say that there is considerable overlap between P. interjectum and P. cambricum. The reference is:
Watsonia 8: 2 July 1970. A revision of some of the taxonomic characters of Polypodium australe Fee. Incidentally, in the acknowledgements, he thanks one W. Elfyn Hughes for information on some of the localities. Does that ring a bell?
Yes, by all means send me a specimen or two of your problematical plants. I note that you can do chromosome counts, which is welcome news, but, as I'm sure that you know, in Polypodium this is complicated by the fact that all of the taxa about which there are usually questions, have the same number of bodies in the spore mother cells. P. interjectum has 111 bivalents. P. x font-queri has 111 univalents. P. x shivasiae has 37 bivalents and 74 univalents. P. x mantoniae has 74 bivalents and 37 univalents. So to distinguish between them by a chromosome count requires a very clear squash and the ability to determine just how many of the bodies present are bivalents and univalents.