Stumped on the hard shoulder

Apologies for bringing this post to the top, but it's an intriguing taxon worth bringing attention to (additional text shown yellow). Using the key to North American Didymodon I was taken on a pretty unambiguous journey to australasiae, a taxon which appears to be recognised in other parts of Europe as well as North America. The last part of the key identifies the key characters separating this species from umbrosus, which even with my limited experience, really looks very different and distinctions are clear. Interestingly David Holyoak's comments on Cornish material indicates that both australasiae and umbrosus occur there, both even confirmed by DNA. Given all this information I'm confused as to why australasiae is not included on the British list.

For the record the following additional images show the extra characters referred to in the key i.e. the bistratose margin towards the leaf tip (NB the proximal 2/3 of the margin is unistratose), strongly papillose cells, quadrate adaxial cells (presenta long the full length of the costa).

As can be seen below, the habitat was very mundane, the species occurring as patches in the outermost zone of colonised dirt (arrowed white, although I think my specimen came from the area indicated by the yellow arrow SN53100107). Direct associates in my sample include Didymodon tophaceus, Barbula unguiculata and Bryum dichotomum. PS. Thanks for the earlier comments, which prompted further examination of my sample.

Maybe it's just because I've had a long day but this one has me stumped. It was growing in the gritty debris of a roadside near Dafen, Llanelli, the most frequent associates including Cochlearia danica, Barbula unguiculata, Plantago coronopus, etc. Help please!