Sunday, 15 November 2015

Mumbles car park revisited - and a lesson learned

Mnium stellare centre-slightly left showing up as a
pale greyish patch with twiggy bits sticking out
Just before getting back in the car after a welcome tea break at the Seaside Cafe by Mumbles Pier, I noticed a nice patch of what I thought was Mnium marginatum and I collected a small sample to double check at home. The main associate was M. stellare and what looked like scattered shoots of Amblystegium serpens, though under the microscope I was struck by the prominent dentate margins on many leaves and I was excited to read that Smith states dentate margins at the widest part of the leaf is the best way to separate Conardia compacta from A. serpens! Unfortunately there were no gemmae on the scrappy material in my small sample and the only rhizoids were arising from just below the leaf insertion point (none found on leaf backs, a Conardia feature). I'm suspecting this is probably just toothy A.s. rather than C.c. but any opinions welcome. I'll take a closer look next time we call in for a cuppa...

What I initially thought was Mnium marginatum, when later examined under the microscope, proved to be just the older shoots of M. stellare. The reddish shoots with elongate leaves and apparent borders (in fact just stained marginal cells) contrasted with the fresh pale green egg-shaped leaves of the new growth - lesson learned.
old M. stellare leaves with darkened marginal cells


  1. In my experience the leaves of Amblystegium sepens are often distinctly toothed, just like the ones in your photo. The drawings in Smith (and Watson) are a bit misleading, although Smith does say that leaf margins can be denticulate.
    Mnium marginatum is a nice record there.

  2. Thanks Charles. It's probably the quality of the habitat that made me look a bit closer than usual and I think sometimes it's possible to look too hard! Anyway, I was very pleased with the Mnium, which was a nice addition to the list for this interesting face of damp Limestone, and which I'm sure still has more to offer.

  3. One of the key features that will separate Mnium marginatum from M. stellare is the leaf border of elongated cells (like most of the other Mniums). Also, in all the Mnium marginatum material I've seen, the upper leaves have the nerve reaching the leaf tip. In these features it resembles small Mium hornum more than Mnium stellare, but unlike Mnium hornum it has clearly decurrent leaf bases. All the Mnium marginatum I've seen has been growing in silty riverside (or canal side) locations. I think George has seen it in similar places on rivers in East Glam.
    The red coloration of your specimens is interesting. Old leaves of Mnium stellare go blue as they senesce. According to Smith this is due to 'the development of mnioindigen in the cytoplasm and cell sap'. Does anybody know where he got that information? It sounds like a blue pigment, although such things are extremely rare in nature. Blue colours are usually the result of complex diffraction mechanisms.

  4. Interesting as it was the red colour of the stem and costa that initially made me consider marginatum. There was no colour in the older leaves that I would describe as blue, although the younger leaves have a glaucous look to them. Perahps the older material had weathered beyond the blue stage?