Plagimnium ... erm ... not quite sure yet ...

Picked up a little moss in Prestonhill Quarry, Inverkeithing, of a "plagiomnium type". At first I thought it would be P.rostratum, but I'm not so sure. starting to lean towards ellipticum but I also know that I don't have all the info I need on another couple of species. The day of buying Smith is coming closer I can tell.It's a good excuse to rummage around in the genus and see what  can learn.

The leaves are very small compared to all the species in the BBS Field Guide, so this plant may be stunted or immature. The shoot size was only 3 or so centimetres. and  I only had a handful of leaves to work with. I do have a reserve plant though which I can re-hydrate to check leaf decurrence again. Nerve is clearly excurrent.

Some images first

Is that decurrent? Maybe a bit? Not hugely though

only c.2.5mm leaf length, by c.1.5

Toothed upper leaf

Can we call that diagonal? I'd say so

One full unit is 25 microns. No obvious Diagonal here, oddly

So ...

* it's not Rhizomnium punctatum, because it has a toothed upper leaf. One down!
* it's not P.cuspidatum because it's not that toothed.
* P.affine, P.elatum, P.medium all have decurrent leaves
* P.affine is quite strongly toothed, has cells in diagonal rows. I'd rule it out on teeth
* P.ellipticum has diagonals; does not have decurrent leaves

Back to P.rostratum, the Field guide differentiates other spp on diagonal cells, but many leaf images of  rostratum online do show diagonal cell arrangement, so I think that's a red herring. Maybe it's a handlens vs. microscope thing. The FG says Affine differs in having cells "longer than wide". Well, in some parts of the leaf this is true and in others not so much!

So, no conclusion yet. Final decision might be in abeyance until somebody can give me a steer.

BBS Field Guide P.rostratum
BBS Field Guide P.affine
BBS Field guide P.ellipticum
BBS Field Guide P.cuspidatum


Nice link to P.ellipticum images