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.

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.

Spring quite literally springing....

It's easy to overlook liverworts. These simple plants were the first to colonise the land and have been around for over 500 million years so in terms of durability, having survived five major mass extinction that wiped out many other life forms, they are unequalled in the plant kingdom. For most of the year they are pretty dull - just a mass of ground-hugging lobed green thalli confined to permanently damp places like the banks of ditches.  But for a few weeks in spring they do something rather extraordinary.


In late winter the surface of a liverwort thallus is a hot-bed of sexual activity. Embedded in the thallus are microscopic pits that release thousands of tiny male cells that swim across wet surfaces using their whirling flagellae. They're heading towards microscopic female structures called archegonia that contain an egg cell and are located under the edge of the thallus. Once fertilisation is achieved a spore capsule forms, like a small dark bead on the surface of the thallus, and when it's ripe the spore capsule stalk begins to elongate - very rapidly.


The images here are of the thalloid liverwort Pellia epiphylla and in the top image you can see a couple of spore capsules with their stalks just beginning to elongate.

After a few hours the stalk (seta) is clearly visible and from this point it elongates very rapidly ..

... so after about a day the whole structure is a couple of inches tall and resembles a match with a glassy stalk.

Then the capsule wall splits open into four segments and the contents literally explode, when elongated, compressed cells called elaters act like springs and hurl the spores into the airstream. You can see the process in more detail and in action by clicking here..... or if you collect some Pellia from the banks of a ditch (woodlands are a good place to look for it) you can watch the whole sequence for yourself.


Simple, primitive but very effective, it has served liverworts well for half a billion years.


There's a nice time lapse sequence of elongating spore capsules of another genus  here.

Liverworts on Springs

Liverworts are not, I have to admit, the most exciting plants - except when their spore capsules explode. These simple plants have been around for over half a billion years, confined to wet places like the muddy banks of streams, where I found this thalloid liverwort called Pellia epiphylla. Liverworts' common name derives from the fact that - if you've got a vivid imagination - their flat lobes look like lobes of green liver and since, according to the mediaeval Doctrine of Signatures, any part of a plant that looked like a part of the human body was supposed to be good for curing its ills, liverworts were assumed to be good for treating liver diseases. Superstition aside, liverworts become a little more interesting at this time of year when they produce these...

.. spherical spore capsules on the surface of the thallus. These change colour, from green to black as they ripen and then suddenly (for a plant) their stems elongate, often overight, raising the capsule aloft on a glassy stalk ....

.... then four vertical splits in the capsule wall become apparent and suddenly (this time, over the course of a few minutes) .....

... the capsule splits open, revealing a mass of green spores interspersed with strange whiskery golden threads.......

.... seen here at higher magnification.

You can see a short video of these writhing threads below .....

Here they are at higher magnification, along with a spore, and below....

... at higher magnification still, when it becomes apparent that each one of those golden threads, known botanically as an elater ...

.... has a helical spring embedded in it. Inside the ripe capsule the springs were all compressed but once the capsule wall splits their force is liberated, hurling out the spores until....

.... only 'springs' and a few remaining spores are left on top of the stalk. Meanwhile most of the spores...

... like this one, magnified here about 400 times, have been scattered to the four winds, to land on some muddy stream bank and germinate to form another thalloid liverwort. It's a cycle that's been going on for half a billion years and is repeated every spring.