Some common mosses and liverworts

 In winter, mosses and liverworts often provide some of the most vibrant new green new plant growth: this is their season. These are a few species that I've encountered in recent weeks.

MOSSES

Cypress-leaved plait-moss Hypnum cupressiforme

One of the commonest and easiest-identified mosses, with leaves all curved in one direction. This one was growing on the top of a fence post in Teesdale.

Hart's-tongue thyme-moss Plagiomnium undulatum.

Unusually large leaves for a moss, with an undulating surface. Growing on the woodland floor beside the river Tees at Egglestone

Silky wall feather-moss Homalothecium sericeum

Often found growing on shady wall tops, but this specimen was on a rotting fallen tree in woodland at Egglestone in Teesdale.

LEAFY LIVERWORTS

Bifid crestwort Lophocolea bidentata

On a damp, shady retaining wall at Hexham in Northumberland

Greater featherwort Plagiochila asplenioides

On the woodkand floor at Egglestone in Teesdale.

THALLOID LIVERWORTS

Forked veilwort Metzgeria furcata

Growing on the fork of a sycamore trunk, where rain trickles down from the branches, at Egglestone in Teesdale. The bifurcating thallus has a central rib.

Crescent-cup liverwort Lunularia cruciata

Growing on concrete beside a drain on the path around our house. Moon-shaped cupules on the thallus are filled with buds (gemmae), each of which will grow into a new liverwort when washed out by rain.

Great scented liverwort aka snakewort Conocephalum conicum. The polygonal pattern on the thallus surface and raised air pores are very distinctive. On a damp, shady retaining wall at Hexham in Northumberland

Endive Pellia Pellia endiviifolia

In winter the tips of the thallus extend into branching lobes. On a damp, shady retaining wall at Hexham in Northumberland

Common liverwort Marchantia polymorpha. Cupules on the surface full of gemmae, like tiddy-winks, that are splashed out by raindrops. Growing around a drain on the edge of the footpath from the Bailey to Prebends bridge in Durham city.

Some lovely liverworts

 This is probably the best time of year to look for liverworts, when they are actively producing new shoots and before taller vegetation grows up around them and often hides them in spring. Here are a few that I've found recently.

Great scented liverwort aka snakewort Conocephalum conicum, growing on a wet, shady retaining wall. This species has a powerful, agreeable scent when you crush it, which to me smells like Duraglit metal polish with citrus undertones. Prominent air pores and the polygonal pattern on the surface, give it a scaly, reptilian appearance.

Pellia endiviifolia, Endive Pellia, a thalloid liverwort whose new growth in autumn and winter consists of irregular, frilly extensions from the end of each flat thallus lobe. I also found this one on a permanently wet, shady retaining wall.

Plagiochila asplenoides, Greater Featherwort, a leafy liverwort that I found growing on a wet, shady bank in open deciduous woodland in Teesdale. One of the commonest leafy liverworts in woodland.

Plagiochila porelloides, Lesser Featherwort. A smaller, more compact Plagiochila species with darker green leaves. I found this one growing in crevices in a wet, shady retaining wall. 

Metzgeria falcata, Forked veilwort, a small thalloid liverwort that I found growing on the bark of an old beech tree, at the point where rain trickles down the trunk. The thin, flat thallus forks near the tip. 

Pellia

Thursday's Guardian Country Diary is all about this very common thalloid liverwort Pellia epiphylla. It's hard to imagine a less charismatic plant but it is remarkable, in several ways.

It's confined to places that are permanently damp, so a shady ditch bank like this suits it well. It consists of a flattened green thallus that's anchored to the substrate by hair-like rhizoids.

Lobes of the thallus overlap and at this time of year make active growth, visible as the brighter green areas in this image.  

If you cut a thin vertical section through the thallus of the liverwort in mid-winter this is what you see (ignore those small, bright objects at the bottom of this image - they are starch grains).Those big round objects embedded in it are male antheridia, full of male sex cells called antherozoids, each of which is just a few thousanths of a millimetre long. Each is equipped with flagellae so when the antheridia burst the antherozoids can swim in the surface film of water. They are heading for .....

.... these female structures called archegonia, situated near the tip of the thallus. There are two here and you can see a dark egg cell inside one of them. The neck of each archegonium emits chemical signals that attract the swimming antherozoids. On mild, wet winter days the whole surface of the liverwort would be covered with tens of thousands of antherozoids, frantically attempting to swim to an archegonium. A few, perhaps assisted by rain splash, make it to their destination, swim down the neck of an archegonium and fertilise the egg cell.

So, in late February and early March, if you get down on your hand and knees with a magnifying glass you can see that this has been the site of very intense sexual activity. The evidence lies in those small, dark spherical structures on the surface. They are the first sign of  capsules full of spores forming, which develop from the fertilised egg.

Within a few days they become larger and darker and begin to rise on stalks - and that's a good time to bring some indoors and watch what happens next.

This picture was taken about 12 hours after the one above and the stalks have grown to about an inch long, while the capsules ...

... have become shiny black spheres.

The capsule stalk continues to grow until it's about three inches long, bending towards the light, then ...

..... the capsule explodes, in slow-motion!

It splits into four segments and a mass of green spores erupts, flicked out by hair-like cells called elaters.

After about five minutes most of the spores have been flicked out and have blown away ...

... leaving behind a mass of writhing elaters, before the stalk collapses

Here, under the microscope at low magnification, you can see the spores and their elaters.

At 400x magnification the structure of the elaters is visible. Each long cell has a spiral of thickening in its wall and when the elater is confined inside the intact capsule it is compressed like a spring. When their confinement is relieved the elaters act as biological springs, hurling out the spores.

Thalloid liverworts are the most ancient living land plants and have a fossil record dating back some 450 million years. When they first evolved those three inch-tall spore capsules would have been the tallest terrestrial vegetation on the planet. 

Today's thalloid liverworts seem to be very similar to their early ancestors. Somehow these simple plants have survived five great mass extinctions and if you measure success in terms of durability alone, then they are unequalled amongst terrestial plants.

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.