Tuesday, 6 January 2015

Racomitrium confusion

I finished the readily identifiable queries from my Tarren y Gigfran excursion, and am now left with a pile of confusing Racomitrium samples! These are all from the sandstone block screes except the first one which was on the crag itself. Sorry for all the photos but hopefully it will help with Racomitrium queries more generally - best to click each one to enlarge it to see more detail.

1: I think this is R. aquaticum: no hair points, fairly blunt leaf tips, dark green colour, slightly papillose cells, margins plane above, recurved below.  And it was on the damp crags rather than the drier sandstone blocks.
2 & 3: these two growing together, near the P. alpinum (now confirmed microscopically btw). The densely tufted plant on the right seems to be R. ericoides (supra-alar cells checked: rectangular not quadrate which rules out elongatum). Some leaves with short hair points, others without them. But the block scree habitat seems a bit odd. The other has long hair points and is possibly heterostichum, though falcate leaves suggest it could be affine.

4 & 5: these two growing together. Both have long hair points, though the plant on the right is more slender and somewhat falcate (not so obvious in the pic). Perhaps both are R. heterostichum?
6: pale green with red stems, somewhat falcate leaves, long hair points. R. heterostichum?

7: this one from sandstone blocks in the woodland. Smaller than the rest, and dark green. No hair points. No idea!

Thanks for any advice.



  1. I agree with the R ericoides, but almost all of the remainder seem likely to be R heterostichum. This can have no hairpoint at all (=R. obtusum in many countries but not accepted in Britain) and I suspect that is what your potential R. aquaticum is. To separate R heterostichum and R affine there is no avoiding cutting cross-sections of the costa. The habitat is plausible for R affine as is the falcate appearance of some plants. Get out your razor blade, or put them on one side until you feel confident wide cross-section cutting!

  2. Thanks Sam. I guess aquaticum wouldn't be as branchy as that. If they are all heterostichum, it's an amazingly variable plant.

    I feared you would suggest costa section cutting - I'll just have to give it another try and hope it goes better than last time!

  3. Hello George,
    I wonder, could I please borrow your top picture for my blog (in an attempt to woo students to the beauties of moss)? I found a specimen that looked exactly similar on a boulder in a little stream on Dartmoor. My colleague and I thought aquaticum too, the cells are super papillose and the leaves are pretty pointy with a strong nerve. The contrasting colours of the sporophyte and the calyptra are just great.