Come on a hunt around the Folk Museum for some of the strangest living things on Earth. They cover many rocks and trees with multi-coloured mosaics, and give a sense of age to walls and buildings, yet we barely notice them. They are lichens.
More than 1200 different species of lichen are found in Ireland. Most of them are known only by their scientific names. You can find out more about these on the Lichen Ireland website but we will look at just a few of those that are easy to spot.
What is a lichen?
Lichens are a remarkable partnership between two completely different kinds of organism – an alga (a single-celled type of plant) and a fungus. Together they can live in places that are impossible for many other living things. The fungal partner attaches to the rocks or tree bark and it protects the algal cells that live within it, These algal cells produce sugar through photosynthesis, some of which goes to the fungal ‘landlord’ in payment.
What we see of a lichen is mainly the fungal partner; the algal cells are buried within it. Some lichens disperse by fungal spores from small discs on the lichen surface; these must combine with algal cells to form a new lichen. Others have powdery patches, formed of a mix of algal and fungal cells, which can be blown by the wind or carried by animals.
The lichen above is Physcia tenella, which does both.
Newly built stone walls, without any lichens, have a harsh appearance compared with those covered with many years of lichen growth. Decades of weathering and lichen growth ‘softens’ the appearance of old stone walls.
Look out for the milestone just up the hill from Coalisland Spade Mill. It is made of limestone and is covered with crusts of several different species of lichen. You would barely notice them but it is these lichens that impart a sense of age to the milestone.
Look on the top and you will see irregular white patches with many tiny white dots. These are actually little pits that the lichen Verrucaria baldensis has excavated in the limestone.
Take a look at the rough stone wall on the road between Coshkib Hill Farm and Coalisland Spade Mill. Some of the rocks, particularly the big boulder by the field gate, have rusty looking patches with small black discs scattered across them. This is Porpidia crustulata, a lichen that extracts iron from the rock to give it this rusty orange colour.
There are plenty of other crustose lichens on these rocks, in shades of grey, brown and yellow. See how many different types you can spot.
Splashes of yellow
On the stone and brickwork around the doorway of Lisrace Forge are yellow patches that might easily be mistaken for the remnants of an old coat of paint. They are actually a thin crusty lichen called Psilolechia lucida. It is a common lichen on sandstone and brick that is slightly sheltered from the rain.
Orange spots on an Orange Hall
Look along the top of the walls outside the Orange Hall to find little clusters of irregular orange spots on a faint grey-green patch a few cm across. This is Protoblastenia rupestris, one of the most common and characteristic lichens growing on concrete.
Lichens, or paint spots?
Look for coloured patches on the windowsills of the houses either side of the sweet shop, on the corner of Tea Lane. Most of them are lichens, although one or two are splashes of paint!
Small circular grey patches with concentric rings of black spots are Rhizocarpon petraeum, a common lichen on sandstone.
The dirty yellow patches are lichens too and, if you look closely, you will see small yellow discs scattered across them. This yellow lichen is Candelariella aurella, another common lichen on sandstone.
Quite often the small discs on lichens look like tiny wine gums or jam tarts. Drop into the sweet shop and check out their wine gums.
Churches and graveyards
The exterior walls of the church in the town area are covered in mortar mixed with broken sea-shells. This rough, lime-rich surface is the perfect home for several different species of lichen. Two of these are particularly easy to find on the front of the building, to either side of the door. One of these is white, from which it gets its name of Lecanora albescens.
The other is orange and its name too comes from the colour; in this instance it is called Caloplaca citrina (think oranges and lemons).
Churches, and particularly graveyards with their diversity of different rock types, are often an important habitat for lichens.
Hundreds of different species of lichen grow on the trunks and branches of trees, often forming a patchwork of tightly attached crusts and leafy clumps of various colours. Many of the larger trees around the Folk Museum have only a poor cover of lichens, probably because they suffered from decades of air pollution blown from the coal fires of Belfast.
The best place to see some of these lichens up close is on the trunks of the young trees on the green opposite Tea Lane.