Brittle bladder-fern

 Brittle bladder-fern Cystopteris fragilis in a shady, damp retaining wall in Teesdale, North Pennines. A beautiful, delicate fern with brittle frond stalks, typically found in crevices in limestone and mortared walls in the northern dales. Growing with hart’s-tongue fern in the third picture.

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.

Pteridomania and an obsession with mutants

Thursday's Guardian Country Diary describes a fragment of mature old woodland at Wolsingham in Weardale whose fallen, decaying trees support a wealth of wildlife, including ...

..... this rather lovely epiphytic polypody fern that was attached to an oak branch that had been torn off by the gales. The golden structures on the underside are the sporangia, ripe and releasing spores. You can read about the full life cycle of ferns by clicking here and see some more close-up and microscope pictures of the sporangia by clicking here.



Picture by Helen Allingham, originally published in the Illustrated London News July 1871
http://en.wikipedia.org/wiki/File:Pteridomania.jpg

The golden age of fern popularity was in Victorian times, during a period that has come to be known as Pteridomania. Then the obsession with collecting and growing these plants reached an all-time high, so much so that the population sizes of some native ferns (like holly fern in Teesdale and all the filmy ferns) were reduced to the point where they are now endangered species in our flora. The ladies in the image above are well equipped for digging up choice ferms, although brambles must have played havoc with those dresses.

Advert from Choice British Ferns: Their Varieties and Culture by Charles T Druery F.L.S.(late 19th. century).

Commercial nurseries like W. andJ Birkenhead made a good living out of selling ferns, club-mosses and selaginellas to those who couldn't get out into the countryside to dig them up. The fern craze generated a wealth of popular and scientific literature on these plants, with books like .....

British Ferns and their Allies: comprising the Ferns, Club-mosses, Pepperworts and Horsetails by Thomas Moore F.L.S., F.H.S. (1881)

...... Thomas Moore's British Ferns and their Allies, which described them and told readers where to find them, as well as providing detailed advice on how to grow and propagate them. 

Remarkably, pteridomania wasn't confined to adults; there were fern books for children, like Francis Heath's Fairy Plants: a Fern Book for Children. In his preface he wrote "There is probably no part of the beautiful realm of Botany capable of offering so much fascination for young people as that which is dominated, so to speak, by ferns; and it is because I can conceive of no branch of a delightful subject so likely to incalcate ideas of gracefulness and to instil elevating, indeed ennobling, thoughts, that I have written a fern book for children".

Decorated initial letter from Fairy Plants: a Fern Book for Children by Francis Heath

I suspect that the thoughts of most 21st. century 12 year-olds, unwrapping such a book given as a present, would be far from ennobling. 

So why did ferns become so popular?

Illustration from Ferns and Fern Culture by J. Birkenhead F.R.H.S. (1897)

One reason was they did well as house plants in shady Victorian drawing rooms dimly lit my gas lamps, especially if they were grown in the humid confines of Wardian cases, like the ornate examples above.

Illustration from Ferns and Fern Culture by J. Birkenhead F.R.H.S. (1897)

Perhaps the ultimate expression of Pteridomaniacal one-upmanship was to construct a shady, rocky fernery in your garden.

Illustration from the Fern World by Francis George Heath (1879)

This, perhaps, was the ideal - a reconstruction of that shady woodland stream where you originally stole your plants from. The picture caption gives some idea of the effect they were hoping to achieve: 'We look with wonder upon a fairy, dreamy scene of clustering ferny forms in fascinating association with mossy rocks an flowing water'.

Another reason was that the elaborate fractal geometry of fern fronds appealed to Victorian arts and craft taste, in jewellery such as this brooch, and in ....



.... garden furniture. The flatness of a fern frond lent itself to recreation in cast iron or in applied patterns on decorative objects.

The fern craze died out in 1914, but not before it had produced one more fascinating botanical obsession, with monstrosities.



Illustration from Ferns of Great Britain and their Allies the Club-mosses, Pepperworts and Horsetails by Anne Pratt (1855)

This is the typical 'wild type' hart's tongue fern Phyllitis scolopendrium.....

Illustration from Choice British Ferns: Their Varieties and Culture by Charles T Druery F.L.S.(late 19th. century).

....... and these are some of the multitude on hart's tongue mutants that Victorian fern-fanciers raised and which many prized as the gems in their collections. Similarly, .....

...... this is the wild type polypody Polypodium vulgare ....

Illustration from Choice British Ferns: Their Varieties and Culture by Charles T Druery F.L.S.(late 19th. century).

...... and these are some of the many mutants of the same species that were cultivated, most unrecognisable as polypody.

Although Gregor Mendel published his experiments in 1865 his discoveries on inheritance remained unrecognised until 1900, so the Victorians knew nothing about the genetic mechanisms that generated such mutants.It would be more than a century before the science of plant developmental genetics would reveal the ways in which simple gene mutations can generate such spectacular variations in leaf developmental pathways.

To the Woods.....

The bluebells in Durham's woodlands are just about at their best now, with the leaf canopy overhead allowing shafts of sunlight to sweep across the mist of blue flowers on the woodland floor. This is a woodmouse-eye-view. In the hot, still humid air the whole of this woodland, just outside Durham city, smelled like a florist's shop....

... but with a few more days of this heat the bluebells will soon begin to fade.

This breathtaking annual display of bluebells has its origins in the previous year's summer. As the flowers fade the plants use the brief window of opportunity before the leaf canopy closes overhead to build up food resreves in a new bulb, where next year's flower initials will already be formed by mid summer. By late summer the leaves will have wilted, leaving only the papery seed heads, while underground next years bulb, primed and ready to go, will sit out the winter ready to burst into life when spring returns. 

Meanwhile, down amongst the bluebells the spreading fronds of buckler fern Dryopteris sp. have already expanded. The whole plant is a living waste-paper basket, catching leaves in that funnel of foliage in autumn and trapping them around the crown of the plant, where they'll decay and create humus around its roots.

Wall ferns

Three tough fern species that remain green throughout the winter and survive all-year-round in a very inhospitable habitat. First up, wall rue (Asplenium ruta-muraria) thrives in the mortar of old walls and walls made of limestone. There are often fine displays on the shady side of churchyard walls and it often turns up on old masonry in the heart of cities.

 

Maidenhair spleenwort (Asplenium trichomanes) is an exceptionally graceful species and is also a lime-lover, so thrives in crumbling mortar wherever there is some shade and humidity.

Polypody fern (Polypodium vulgare) is an epiphyte – a plant that grows on other plants – and its natural habitat is on moss-covered branches of trees but in Weardale it often makes itself at home in between the capstones of drystone walls. It’s an evergreen fern and if you turn the fronds over even this late in the year you’ll often get a surprise – bright yellow clusters of sporangia on the underside of the fronds.

For a closer look at these hop over to http://beyondthehumaneye.blogspot.com/2009/11/polypody-fern-with-golden-sporangia.html