There are, according to the standard work on British lichens, 1873 different species found in the UK and Ireland, which means that there are roughly 25 per cent more types of lichen than there are flowering plants. 300 of these lichens have, according to Allan Pentecost, been recorded from the area around Malham Tarn. Here are few photographs to give you some idea of their diversity.
Verrucaria baldensis and V. nigrescens on a vertical limestone face near Malham Tarn field centre, April 2014.
We found two crustose species of the genus Verrucaria growing side by side on a limestone wall. These crust-forming lichens secrete organic acids which dissolve the rock beneath them and allow the fungal hyphae to penetrate deeper. Some of the black spots on the left hand lichen (V. baldensis) may be fruiting bodies but most are tiny pits in the lichen surface.
Left hand image: Gyalecta jenensis on vertical limestone near the field centre with (inset) examples on a twig. The discs are about 3-4 millimetres across. The right hand image shows the foliose lichen, Platismatia glauca on a branch (approx. two centimetres diameter).
The circular structures on the left hand image, which were christened “jammy dodgers” by the class, are actually the fruiting bodies (“apothecia”) of a thin grey crustose lichen called Gyalecta jenensis. The right hand image is a grey-green foliose (“leafy”) lichen called Platismatia glauca growing on a branch in an area of alder Carr near the field centre.
Porpidia tuburculosa (left) and P. macrocarpa (right) on a Millstone Grit wall on the Malham Tarn estate, April 2014.
Lichens grow in such intimate contact with their substrate that the type of rock can have a big influence on the species of lichens that are found. Whilst the rock underlying the Malham Tarn area is Carboniferous Limestone, Millstone Grit, another local stone, is also used in walls and buildings. Two of the most prominent lichens on this stone (which is much less base rich) are illustrated above. Porpidia tuburculosa has the informal name “cigarette ash lichen”, due to the grey speckles of soredia (asexual propagation organs) scattered over the surface. The other species illustrated, P. macrocarpa, has some reddish-brown patches of iron oxide, which may have been dissolved from the rock matrix by the organic acids produced by the lichen, and then deposited amongst the fungal hyphae which make up much of the lichen thallus.
Cladonia coniocraea and C. fimbriata growing on a branch in the alder Carr area of Malham Tarn NNR, April 2014. The tallest podetia are about two centimetres high.
The final image for this post shows two representatives of a large genus of fruticose (“bushy” or “beard-like”) lichens called Cladonia. These have upright structures called “podetia”, at the top of which the apothecia are found. The left hand specimens in this photograph, Cladonia coniocraea, have podetia that bend and gradually taper towards the tip whilst, at the centre, there are two podetia shaped like golf tees. These belong to a different species, C. fimbriata.