Fence post lichen garden

Maybe it's time someone produce a survey of the flora of rotting fence posts. There are so many fascinating and often beautiful examples of these miniature gardens, colonised by mosses, lichens, fungi and flowering plants, where the water retentive end-grain of the wood provides just enough moisture for the organisms to survive throughout the year. 

Pixie-cup lichens Cladonia spp. are some of the commonest colonisers. I noticed this exquisite example on the site of the former Brancepeth colliery at Willington in County Durham.

 

A Golden Wall

Thursday's Guardian Country Diary is about this remarkable 'golden' wall at Hexham, in Northumberland's Tyne valley. It's a retaining wall beside the main Carlisle to Newcastle railway line, that crosses the Tyne just beyond that bridge in the distance and passes this point at head height.

The golden covering is caused by an alga called Trentepohlia aurea.

It spends the drier months of the year as a  powdery deposit on rocks and tree trunks but when it's wet the alga grows into a forest of minute filaments, forming a dense mat on the surface.

You can see the filaments in this close-up, grouped together to form golden cushions that are a few millimetres in diameter. This wall is constantly wet, due to water percolating through from the railway track bed, so conditions are near-perfect for the growth of the alga.

When the tufts coalesce into a golden carpet they provides a very striking back-drop for other plants that are colonising the wall, like this ivy and .....

The liverwort Conocephalum conicum, also known as snakewort. Its surface is divided into small polygons, each with an air pore at its centre, giving it a resemblance to green snakes' skin.

There are other liverworts on the wetter sections of the wall, including this one which I think is Pellia endiviifolia.

The crevices are home to mosses and this little fern with leathery fronds - wall rue Asplenium ruta-muraria.

The alga seems to thrive particularly well on the cement but there are patches of lichen on some of the stones. A close look at this one revealed ....

.... these fungal fruiting bodies, which look like tiny pink toadstools. I think this is a species in the genus Baeomyces.

Another lichen, this time .....

... with fruiting bodies (apothecia)  that look like minute disks of liquorice. A species of Lecidea?

This lichen is a Cladonia species, probably C. fimbriata

Lichens are formed by the symbiotic association between a fungus and an alga and it's very likely that the algal symbiont of some of the lichens on this wall is Trentepohlia. 

Back now for a closer look at the alga Trentepohlia, this time under the microscope.

Under low magnification (c. x40) with a stereo-microscope you can see the forest of algal filaments that make up those orange cushions, while ....

....... here, under a compound microscope (x100) you can see the cells that make up the filaments, and .....

.... at a higher magnification still (c. x400) you can see the granular, pigmented contents of the cells.

There are animals living in the crevices in this wall, including the fearsome snake-back spider - but that's another story.

Lichens

Thursday's Guardian Country Diary explores the wonderful world of lichens that are the brightest objects on moorland in winter. Lichens like .....

...... this delightful Cladonia diversa (?), tipped with what looks like scarlet sealing wax. Those red tips are the apothecia, where microscopic flask-shaped asci shoot their fungal spores out into the breeze. To form another lichen they need to land close enough to the correct alga for the two to form a symbiotic union and develop into a lichen.

This is the moorland described in the Country Diary - a high, windswept path over Birkside Fell above Blanchland, in the Derwent valley on the Durham-Northumberland border. The high rainfall means that nutrients are rapidly leached out of the sandy soil. The area to the right is grouse moor, which from a distance seems like is a sea of dull brown vegetation, until .....

.... you look at what is going on at grouse-eye level, under the canopy of gorse bushes. There, at this time of year, the lichens are at their best and the mosses are actively growing too.

There's a wide range of lichen form and colour. I think this is Cladonia macilenta (?)

..... this looks like Peltigera lactucifolia (?)

.... and this, looking like a forest of tiny golf tees, is Cladonia pyxidata (?)

N.B. the (?) after the specific names mean that these are tentative IDs - I need to check them more carefully to be certain!

Where the Bodies are Buried ...

Today's Guardian Country Diary describes a field excursion with some Durham University biology students to Chapel Fell, between Weardale and Teesdale in Co. Durham 


We were lucky from the weather and the views were stunning, although there were still patches of snow on the ground so it was pretty bracing up there. This is just about the last place in the local landscape to show signs of spring but if you take your eyes off the view and look at the ground under your feet there are plenty of signs of growth in the upland mosses. Some beautiful lichens thrive here too.

Bogs like this are deep pools filled with Sphagnum moss and are a potential death trap. Stroll onto this fine green 'lawn' and you'd instantly disappear up to your neck (at least) in ice-cold water. 

Sphagnum moss is a living sponge that retains vast amounts of water, thanks to its unique leaf structure which you can see by clicking here. Once you get about a metre down from the surface it's pretty anaerobic and preserves biological materials (like drowned bodies) extremely well. You can read about some fine examples of corpses exhumed from peat bogs by clicking here.

In more open patches of water the moss takes on this very attractive starry appearance.

Sphagnum species identification is a specialist skill (there are around 36 species listed in the latest field guide) that I've never mastered and there are several species up here that would keep dedicated bryologists occupied for some time, including ...

.... this delightful claret-coloured example.

One day I'll learn to identify them, using his excellent key.

Polytrichum species thrive on the drier banks ....

.... and  this one,  which I think is Hylocomium splendens, has intensely red stems bearing yellowish leaves and does well amongst the heather stems that have yet to show much sign of new growth. 

This is also home to some fine lichens (mostly Cladonia species) .....

I think this may be Cladonia diversa