Brachythecium glareosum

Several Bryophyte guides mention the problems of distinguishing Brachythecium glareosum from Homalothecium lutescens and Brachythecium rutabulum in the field. All three species occur along forest tracks in NPT, sometimes together, and on more than one occasion I have mistaken  B. glareosum for one or other of the other two. This winter I've tried to sort this out and I thought it might be useful if I posted some comparative observations. However, there is nothing new here and I apologise if I appear to be teaching my grandmother how to suck eggs.
In its typical form, B. glareosum appears to be quite distinct with those long, slightly twisted acumens at the tips of the leaves, which form conspicuous, pointed clusters of bristles at the apex of the stems and branches. This is a major feature used by Smith to distinguish B. glareosum from all the other Brachytheciums. 

                                    Brachythecium glareosum, forest track, Glyncorrwg

                     Long, bristly stem tips of Brachythecium glareosum (note distinct pleats on leaves)

Confusion with H. lutescens arises because it too has a long fine point to its leaves and both species also have clearly pleated leaves.

                                                             Homalothecium lutescens

                                                         Homalothecium lutescens

The leaves of H. lutescens are narrower and more triangular than those of B. glareosum and the pleats on the leaves are very prominent and almost parallel. Also, H. lutescens can be distinguished from any Brachythecium if you examine a leaf under the microscope. Leaf cells are very narrow, and the basal cells of the leaf are distinctly thick walled (incrassate).

                  Part of Homalothecium lutescens leaf showing  thick-walled (porose) basal cells

'Typical' Brachythecium rutabulum is usually not a problem. Confusion occurs when you encounter specimens with long drawn out tips to their leaves, which happens frequently. Even then, however, B. rutabulum rarely exhibits the long, conspicuous, bristly stem tips that characterise B. glareosum. Most texts refer to the twisted leaf tips of B. glareosum, but this is not always a very prominent feature in my experience.

 Brachythecium rutabulum (note vaguely pleated leaves)

There are other subtle differences between B. rutabulum and B. glareosum that can be observed in the field. The leaves of B. glareosum are narrower than those of B. rutabulum, (although not as narrow as H. lutescens), and more noticeably pleated. The typical habit of B. rutabulum always seems to be plumper and more robust to me, compared to the slender, graceful and more prostrate habit of B. glareosum, reminiscent of Homalothecium. B. glareosum is a calcicole and on forest tracks usually occurs with species like Ctenidium molluscum, Ditrichum gracile and Trichostomum crispulum.

The leaves of B. glareosum and B. rutabulum look different under the microscope. The alar cells of B. rutabulum tend to be long-rectangular and form decurrent tongues (almost like auricles), and the upper leaf border is clearly toothed.

                                                  Long-rectangular alar cells of B. rutabulum

                                                        Teeth on upper part of leaf of B. rutabulum

The alar cells of B. glareosum are short rectangular and not decurrent, and the leaf has very indistinct teeth.

Short-rectangular alar cells of B. glareosum

Indistinct teeth on upper part of leaf of B. glareosum

Commonest bryophyte species

Julita Klusa has just put a link to her list of Latvia's top 20 commonest bryophytes on Twitter.  It is fascinatingly different to the top 20 in south Wales!

Rank	Pembrokeshire (SW Wales)	Latvia	UK notes
1	Kindbergia praelonga	Hypnum cupressiforme	Abundant (No. 2 in Pembrokeshire)
2	Hypnum cupressiforme	Leucodon sciuroides	Uncommon and very local
3	Brachythecium rutabulum	Hylocomium splendens	Locally abundant but habitat specific
4	Frullania dilatata	Plagiomnium undulatum	Locally abundant but habitat specific
5	Metzgeria furcata	Pleurozium schreberi	Locally abundant but habitat specific
6	Lophocolea bidentata	Rhytidiadelphus triquetrus	Locally abundant but habitat specific
7	Isothecium myosuroides	Dicranum scoparium	Locally abundant but habitat specific
8	Bryum dichotomum	Climacium dendroides	Uncommon and local
9	Mnium hornum	Orthotrichum speciosum	Rare and eastern, not in Wales
10	Tortula muralis	Radula complanata	Increasing and locally abundant
11	Bryum capillare	Atrichum undulatum	Abundant (No. 12 in Pembrokeshire)
12	Atrichum undulatum	Nowellia curvifolia	Locally abundant but habitat specific
13	Ulota phyllantha	Rhytidiadelphus squarrosus	Locally abundant but habitat specific
14	Dicranella heteromalla	Eurhynchium angustirete	Not British
15	Bryum argenteum	Homalia trichomanoides	Locally abundant but habitat specific
16	Calliergonella cuspidata	Ptilium crista-castrensis	Uncommon and north-eastern
17	Fissidens bryoides	Plagiochila asplenioides	Locally abundant but habitat specific
18	Thuidium tamariscinum	Syntrichia ruralis	Locally abundant but habitat specific
19	Didymodon insulanus	Neckera pennata	Extinct in Britain, one historic record
20	Ulota bruchii	Plagiomnium cuspidatum	Uncommon and very local

This has got me thinking again what a pity it is that the South Wales Bryophyte Blog is only visible to 'members' and I wonder whether we could make it more visible but with commenting and blogging limited to 'members'.