Llanelli Naturalists Newsletter - Winter 1990/1991
R.N. Stringer & R.H. Davies

During the last twelve months an attempt has been made to contribute to the lichen records of the county. Due to the need for expensive specialist equipment (high powered microscopes) to aid identification this group of primitive plants has been sadly neglected in the past. This is reflected in the membership to the British Lichen Society which has only 14 members throughout Wales and only 2 in Dyfed. Whilst this has advantages in that the Dyfed A.G.M. can be held in a telephone kiosk at minimal cost it also means that recording proceeds at the same growth rate of many lichen species (very slowly!).

Nevertheless, the authors have contributed to the distribution records over the last year, and to date a total of over 500 species have been recorded for the county out of a British total of about 1600. Lichens are usually found in habitats which are unfavourable for the growth of higher plants but can occur in the same location as certain mosses and liverworts. Environmental conditions in these habitats tend to be extreme and hence growth rates are low and the size of the resulting thallus (the lichen body) is small which causes problems in locating the specimen, and, in its identification.

Most lichens occur on either rock 'saxicolous' or bark 'corticolous' substrates. Some species are specific to the rock type and similarly, on bark, some lichens are only associated with particular tree species or the age of the tree. Bark substrates can vary from smooth to rough and can be chemically different between trees, or from the top of one tree to tis base; consequently a variety of microhabitats occur. Also, an over-riding factor determining the distribution of lichens is the degree of aerial pollution. Lichens are extremely pollution-sensitive so their distribution patterns are governed by their proximity to industrial centres and urban areas.

Coastal locations are particularly rewarding and one site close to Llanelli has been found to contain a lichen rich flora. This is St. Ishmael's Church (SN363083) near Ferryside which is a good site because it is away from polluting influences, and, as well as containing a wide variety of 'rock types' in the form of gravestones and the church building itself, it also contains a few large trees in the vicinity.

The church is built mainly of limestone*and this is colonised by Verrucoria species (V. hochstetteri and V. sphinctrina) which are white in colour and contain minute pits on the thallus surface which contain the sporulating structures. The yellowish colonies belong to Caloplaca species which produce characteristic yellow disc-shaped sporulating structures on the thallus surface. Both Verrucaria and Caloplaca species are indicative of a limestone substate but the mortar is also colonised by a particular species (P. niderosiensis) which imparts a pink colouration to the substrate. The gravestones, most of which are marble are extensively covered with a white lumpy lichen (Ochrolecia parella) which forms large patches up to 20cm across. In previous times it was used for dyeing and may have been the source of the purple dye 'perelle'. The other white-coloured lichen thallus which contains black circular ascocarps on the surface is Lecanora atra. These well-covered gravestones contrast with the slate tombstones which are only colonised by a green lichen Lecanora muralis. Some of the tops of the gravestones and especially the ridge tiles of the church (*actually mildly calcareous Old Red Sandstone - Ed) roof are colonised by a yellow-orange, rather chunky lichen Xanthoria parietina. This requires bright sunlight and also nutrient rich substrates to succeed and its common occurrence on the roof and tops of gravestones is entirely due to bird activity. They perch on high spots and the droppings are rich in nitrogen and phosphate which are utilised by the lichen. Most of the south-facing surfaces are well covered in lichens but the north-facing and shaded areas are not so well colonised, and, only support the presence of a powdery mealy-green lichen Lepraria incana.

The trees in the churchyard are also substantially covered by lichen species. The dominant community is the Ramalina/Parmelia type which are fleshier and have more structure than those species occuring on the stone substrate. The Parmelia species (P. pereata, caperata) are those characteristic of unpolluted areas, and as a consequence a high diversity of species are present on the bark - Lecanora, Pertusaria, Xanthoria, Opegrapha and Graphis species.

Over 40 species have been recorded from the churchyard which is very good compared to other areas of Britain. Many of the species found on gravestones are used to monitor growth rates because tombstones are dated and can give invaluable information on the decline or increase in species due to atmospheric conditions. Thus churchyards are notable habitats for lichens (as well as for flowering plants) and are a very useful starting point for anybody studying lichens, either their distribution or their physiology.