Saturday, 20 January 2018

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!


  1. Reflecting on it now, it looks like Didymodon tophaceus, but not typical in several ways. I'd still welcome any thoughts.

  2. Some of the leaves from the side look a bit Trichostomum crispulum like. Could this be a possibility?

    1. The leaves hardly change shape upon drying, which would rule out Tc

  3. My first thought was Didymodon tophaceus - it looks very similar to some I saw on the VC35 seawall. However, the hyaline base and resemblance to T. crispulum brings D umbrosus into the reckoning... I don't think it's that species, but it might be worth cutting some leaf cross-sections to see if the margin is bistratose.

  4. If it wasn't for the fact that typical tophaceus was present alongside, I may have recorded it as such, but there was definitely something different about it in the field that called out for closer scrutiny.

  5. Well done Barry. I believe that Tom Blockeel, David Holyoak and Jan Kucera have discussed Didymodon australasiae as a separate British species; it's mentioned in the Atlas too. I suggest you email Tom for his thoughts on the subject. Your plant seems to match the description very well, and is totally different to the D. umbrosus I have seen a few times on damp walls in south Wales. I wondered whether my VC35 roadside Didymodon (click umbrosus in the labels) might also be D australasiae, but the photos suggest not.